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Sample records for doped ceo2 ceramics

  1. Bioactivity of Y2O3 and CeO2 doped SiO2-SrO-Na2O glass-ceramics.

    PubMed

    Placek, L M; Keenan, T J; Wren, A W

    2016-08-01

    The bioactivity of yttrium and cerium are investigated when substituted for Sodium (Na) in a 0.52SiO2-0.24SrO-0.24-xNa2O-xMO glass-ceramics (where x = 0.08 and MO = Y2O3 or CeO2). Bioactivity is monitored through pH and inductively coupled plasma-optical emission spectrometry where pH of simulated body fluid ranged from 7.5 to 7.6 and increased between 8.2 and 10.0 after 14-day incubation with the glass-ceramic disks. Calcium (Ca) and phosphorus (P) levels in simulated body fluid after incubation with yttrium and cerium containing disks show a continual decline over the 14-day period. In contrast, Con disks (not containing yttrium or cerium) caused the elimination of Ca in solution after 1 day and throughout the incubation period, and initially showed a decline in P levels followed by an increase at 14 days. Scanning electron microscopy and energy dispersive spectroscopy confirmed the presence of Ca and P on the surface of the simulated body fluid-incubated disks and showed precipitates on Con and HCe (8 mol% cerium) samples. Cell viability of MC3T3 osteoblasts was not significantly affected at a 9% extract concentration. Optical microscopy after 24 h cell incubation with disks showed that Con samples do not support osteoblast or Schwann cell growth, while all yttrium and cerium containing disks have direct contact with osteoblasts spread across the wells. Schwann cells attached in all wells, but only showed spreading with the HY-S (8 mol% yttrium, heated to sintering temperature) and YCe (4 mol% yttrium and cerium) disks. Scanning electron microscopy of the compatible disks shows osteoblast and sNF96.2 Schwann cells attachment and spreading directly on the disk surfaces. PMID:27231265

  2. Origin of enhanced photocatalytic activity of F-doped CeO2 nanocubes

    NASA Astrophysics Data System (ADS)

    Miao, Hui; Huang, Gui-Fang; Liu, Jin-Hua; Zhou, Bing-Xin; Pan, Anlian; Huang, Wei-Qing; Huang, Guo-Fang

    2016-05-01

    CeO2 nanoparticles are synthesized using a low-temperature solution combustion method and subsequent heat treatment in air. It is found that F-doping leads to smaller particle size and the formation of CeO2 nanocubes with higher percentage of reactive facets exposed. The band gap is estimated to be 3.16 eV and 2.88 eV, for pure CeO2 and fluorine doped CeO2 (F-doped CeO2) nanocubes, respectively. The synthesized F-doped CeO2 nanocubes exhibit much higher photocatalytic activities than commercial TiO2 and spherical CeO2 for the degradation of MB dye under UV and visible light irradiation. The apparent reaction rate constant k of MB decomposition over the optimized F-doped CeO2 nanocubes is 9.5 times higher than that of pure CeO2 and 2.2 times higher than that of commercial TiO2. The enhanced photocatalytic activity of F-doped CeO2 nanocubes originates from the fact that F-doping induces the small size, the highly reactive facets exposed, the intense absorption in the UV-vis range and the narrowing of the band gap. This research provides some new insights for the synthesis of the doping of the foreign atoms into photocatalyst with controlled morphology and enhanced photocatalytic activity.

  3. Photocatalytic degradation of methyl orange by CeO2 and Fe-doped CeO2 films under visible light irradiation.

    PubMed

    Channei, D; Inceesungvorn, B; Wetchakun, N; Ukritnukun, S; Nattestad, A; Chen, J; Phanichphant, S

    2014-01-01

    Undoped CeO2 and 0.50-5.00 mol% Fe-doped CeO2 nanoparticles were prepared by a homogeneous precipitation combined with homogeneous/impreganation method, and applied as photocatalyst films prepared by a doctor blade technique. The superior photocatalytic performances of the Fe-doped CeO2 films, compared with undoped CeO2 films, was ascribed mainly to a decrease in band gap energy and an increase in specific surface area of the material. The presence of Fe(3+) as found from XPS analysis, may act as electron acceptor and/or hole donor, facilitating longer lived charge carrier separation in Fe-doped CeO2 films as confirmed by photoluminescence spectroscopy. The 1.50 mol% Fe-doped CeO2 film was found to be the optimal iron doping concentration for MO degradation in this study.

  4. Role of vacancies, light elements and rare-earth metals doping in CeO2.

    PubMed

    Shi, H; Hussain, T; Ahuja, R; Kang, T W; Luo, W

    2016-01-01

    The magnetic properties and electronic structures of pure, doped and defective cerium oxide (CeO2) have been studied theoretically by means of ab initio calculations based on the density function theory (DFT) with the hybrid HF/DFT technique named PBE0. Carbon (C), nitrogen (N), phosphorus (P), sulphur (S), lanthanum (La) and praseodymium (Pr) doped in CeO2 and CeO2 containing oxygen vacancies (Ov) were considered. Our spin-polarized calculations show that C, N, Pr dopants and Ov defects magnetize the non-magnetic CeO2 in different degree. The optical band gap related to photocatalysis for pure CeO2, corresponding to the ultraviolet region, is reduced obviously by C, N, S, Pr impurities and oxygen vacancies, shifting to the visible region and even further to the infrared range. Especially, N-, S- and Pr-doped CeO2 could be used to photocatalytic water splitting for hydrogen production. As the concentration of Ov increasing up to 5%, the CeO2 exhibits a half-metallic properties. PMID:27554285

  5. Role of vacancies, light elements and rare-earth metals doping in CeO2

    PubMed Central

    Shi, H.; Hussain, T.; Ahuja, R.; Kang, T. W.; Luo, W.

    2016-01-01

    The magnetic properties and electronic structures of pure, doped and defective cerium oxide (CeO2) have been studied theoretically by means of ab initio calculations based on the density function theory (DFT) with the hybrid HF/DFT technique named PBE0. Carbon (C), nitrogen (N), phosphorus (P), sulphur (S), lanthanum (La) and praseodymium (Pr) doped in CeO2 and CeO2 containing oxygen vacancies (Ov) were considered. Our spin-polarized calculations show that C, N, Pr dopants and Ov defects magnetize the non-magnetic CeO2 in different degree. The optical band gap related to photocatalysis for pure CeO2, corresponding to the ultraviolet region, is reduced obviously by C, N, S, Pr impurities and oxygen vacancies, shifting to the visible region and even further to the infrared range. Especially, N-, S- and Pr-doped CeO2 could be used to photocatalytic water splitting for hydrogen production. As the concentration of Ov increasing up to 5%, the CeO2 exhibits a half-metallic properties. PMID:27554285

  6. Role of vacancies, light elements and rare-earth metals doping in CeO2.

    PubMed

    Shi, H; Hussain, T; Ahuja, R; Kang, T W; Luo, W

    2016-08-24

    The magnetic properties and electronic structures of pure, doped and defective cerium oxide (CeO2) have been studied theoretically by means of ab initio calculations based on the density function theory (DFT) with the hybrid HF/DFT technique named PBE0. Carbon (C), nitrogen (N), phosphorus (P), sulphur (S), lanthanum (La) and praseodymium (Pr) doped in CeO2 and CeO2 containing oxygen vacancies (Ov) were considered. Our spin-polarized calculations show that C, N, Pr dopants and Ov defects magnetize the non-magnetic CeO2 in different degree. The optical band gap related to photocatalysis for pure CeO2, corresponding to the ultraviolet region, is reduced obviously by C, N, S, Pr impurities and oxygen vacancies, shifting to the visible region and even further to the infrared range. Especially, N-, S- and Pr-doped CeO2 could be used to photocatalytic water splitting for hydrogen production. As the concentration of Ov increasing up to 5%, the CeO2 exhibits a half-metallic properties.

  7. Role of vacancies, light elements and rare-earth metals doping in CeO2

    NASA Astrophysics Data System (ADS)

    Shi, H.; Hussain, T.; Ahuja, R.; Kang, T. W.; Luo, W.

    2016-08-01

    The magnetic properties and electronic structures of pure, doped and defective cerium oxide (CeO2) have been studied theoretically by means of ab initio calculations based on the density function theory (DFT) with the hybrid HF/DFT technique named PBE0. Carbon (C), nitrogen (N), phosphorus (P), sulphur (S), lanthanum (La) and praseodymium (Pr) doped in CeO2 and CeO2 containing oxygen vacancies (Ov) were considered. Our spin-polarized calculations show that C, N, Pr dopants and Ov defects magnetize the non-magnetic CeO2 in different degree. The optical band gap related to photocatalysis for pure CeO2, corresponding to the ultraviolet region, is reduced obviously by C, N, S, Pr impurities and oxygen vacancies, shifting to the visible region and even further to the infrared range. Especially, N-, S- and Pr-doped CeO2 could be used to photocatalytic water splitting for hydrogen production. As the concentration of Ov increasing up to 5%, the CeO2 exhibits a half-metallic properties.

  8. Structural and dielectric properties of Cu doped CeO2

    NASA Astrophysics Data System (ADS)

    Kumar, Pawan; Chand, F.; Kumar, Parmod; Meena, R. C.; Kumar, Ashish; Asokan, K.

    2016-05-01

    In the present work, we report the structural and dielectric properties of Cu doped CeO2 compounds synthesized by solid state reaction method. X-ray diffraction study confirms the formation of cubic phase with Fm-3m space group corresponding to fluorite CeO2 structure. The crystallite size was found to decrease with Cu concentration. Furthermore, the dielectric measurements were carried out by varying frequency in the temperature range of 120 to 380 K. It has been found that the increase in Cu concentration in the host lattice leads to an enhancement in dielectric constant.

  9. Facile synthesis of ferromagnetic Ni doped CeO2 nanoparticles with enhanced anticancer activity

    NASA Astrophysics Data System (ADS)

    Abbas, Fazal; Jan, Tariq; Iqbal, Javed; Ahmad, Ishaq; Naqvi, M. Sajjad H.; Malik, Maaza

    2015-12-01

    NixCe1-xO2 (where x = 0, 0.01, 0.03, 0.05 and 0.07) nanoparticles were synthesized by soft chemical method and were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman, UV-vis absorption spectroscopy and vibrating sample magnetometer (VSM). XRD and Raman results indicated the formation of single phase cubic fluorite structure for the synthesized nanoparticles. Ni dopant induced excessive structural changes such as decrease in crystallite size as well as lattice constants and enhancement in oxygen vacancies in CeO2 crystal structure. These structural variations significantly influenced the optical and magnetic properties of CeO2 nanoparticles. The synthesized NixCe1-xO2 nanoparticles exhibited room temperature ferromagnetic behavior. Ni doping induced effects on the cytotoxicity of CeO2 nanoparticles were examined against HEK-293 healthy cell line and SH-SY5Y neuroblastoma cancer cell line. The prepared NixCe1-xO2 nanoparticles demonstrated differential cytotoxicity. Furthermore, anticancer activity of CeO2 nanoparticles observed to be significantly enhanced with Ni doping which was found to be strongly correlated with the level of reactive oxygen species (ROS) production. The prepared ferromagnetic NixCe1-xO2 nanoparticles with differential cytotoxic nature may be potential for future targeted cancer therapy.

  10. Effect of poling process on piezoelectric properties of BCZT - 0.08 wt.% CeO2 lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Chandrakala, E.; Praveen, J. Paul; Das, Dibakar

    2016-05-01

    The properties of lead free piezoelectric materials can be tuned by suitable doping in the A and B sites of the perovskite structure. In the present study, cerium has been identified as a dopant to investigate the piezoelectric properties of lead-free BCZT system. BCZT - 0.08 wt.%CeO2 lead-free ceramics have been synthesized using sol-gel technique and the effects of CeO2 dopant on their phase structure and piezoelectric properties were investigated systematically. Poling conditions, such as temperature, electric field, and poling time have been optimized to get enhanced piezoelectric response. The optimized poling conditions (50°C, 3Ec and 30min) resulted in high piezoelectric charge coefficient d33 ~ 670pC/N, high electromechanical coupling coefficient kp ~ 60% and piezoelectric voltage coefficient g33 ~ 14 mV.m/N for BCZT - 0.08wt.% CeO2 ceramics.

  11. Hierarchically mesostructured doped CeO2 with potential for solar-cell use

    NASA Astrophysics Data System (ADS)

    Corma, Avelino; Atienzar, Pedro; García, Hermenegildo; Chane-Ching, Jean-Yves

    2004-06-01

    Many properties provided by supramolecular chemistry, nanotechnology and catalysis only appear in solids exhibiting large surface areas and regular porosity at the nanometre scale. In nanometre-sized particles, the ratio of the number of atoms in the surface to the number in the bulk is much larger than for micrometre-sized materials, and this can lead to novel properties. Here we report the preparation of a hierarchically structured mesoporous material from nanoparticles of CeO2 of strictly uniform size. The synthesis involves self-assembly of these 5-nm CeO2 pre-treated nanoparticles in the presence of a structure directing agent (poly(alkylene oxide) block polymer). The walls of this hexagonal structured CeO2 material are formed from the primary nanoparticles. The material possesses large pore volumes, high surface areas, and marked thermal stability, allowing it to be easily doped after synthesis whilst maintaining textural and mechanical integrity. It also exhibits a photovoltaic response, which is directly derived from the nanometric particle size-normal CeO2 does not show this response. We have constructed operational organic-dye-free solar cells using nanometric ceria particles (in both mesostructured or amorphous forms) as the active component, and find efficiencies that depend on the illuminating power.

  12. A facile synthesis of high quality nanostructured CeO2 and Gd2O3-doped CeO2 solid electrolytes for improved electrochemical performance.

    PubMed

    Kuo, Yu-Lin; Su, Yu-Ming; Chou, Hung-Lung

    2015-06-01

    This study describes the use of a composite nitrate salt solution as a precursor to synthesize CeO2 and Gd2O3-doped CeO2 (GDC) nanoparticles (NPs) using an atmospheric pressure plasma jet (APPJ). The microstructures of CeO2 and GDC NPs were found to be cubical and spherical shaped nanocrystallites with average particle sizes of 10.5 and 6.7 nm, respectively. Reactive oxygen species, detected by optical emission spectroscopy (OES), are believed to be the major oxidative agents for the formation of oxide materials in the APPJ process. Based on the material characterization and OES observations, the study effectively demonstrated the feasibility of preparing well-crystallized GDC NPs by the APPJ system as well as the gas-to-particle mechanism. Notably, the Bader charge of CeO2 and Ce0.9Gd0.1O2 characterized by density function theory (DFT) simulation and AC impedance measurements shows that Gd helps in increasing the charge on Ce0.9Gd0.1O2 NPs, thus improving their conductivity and making them candidate materials for electrolytes in solid oxide fuel cells.

  13. A facile synthesis of high quality nanostructured CeO2 and Gd2O3-doped CeO2 solid electrolytes for improved electrochemical performance.

    PubMed

    Kuo, Yu-Lin; Su, Yu-Ming; Chou, Hung-Lung

    2015-06-01

    This study describes the use of a composite nitrate salt solution as a precursor to synthesize CeO2 and Gd2O3-doped CeO2 (GDC) nanoparticles (NPs) using an atmospheric pressure plasma jet (APPJ). The microstructures of CeO2 and GDC NPs were found to be cubical and spherical shaped nanocrystallites with average particle sizes of 10.5 and 6.7 nm, respectively. Reactive oxygen species, detected by optical emission spectroscopy (OES), are believed to be the major oxidative agents for the formation of oxide materials in the APPJ process. Based on the material characterization and OES observations, the study effectively demonstrated the feasibility of preparing well-crystallized GDC NPs by the APPJ system as well as the gas-to-particle mechanism. Notably, the Bader charge of CeO2 and Ce0.9Gd0.1O2 characterized by density function theory (DFT) simulation and AC impedance measurements shows that Gd helps in increasing the charge on Ce0.9Gd0.1O2 NPs, thus improving their conductivity and making them candidate materials for electrolytes in solid oxide fuel cells. PMID:25959436

  14. Interplay of structural, optical and magnetic properties in Gd doped CeO2

    NASA Astrophysics Data System (ADS)

    Soni, S.; Kumar, Sudish; Meena, R. S.; Vats, V. S.; Dalela, S.

    2015-06-01

    In this research wok systematic investigation on the synthesis, characterization, optical and magnetic properties of Ce1-xGdxO2 (where x=0.02, 0.04, 0.06, and 0.10) synthesized using the Solid-state method. Structural, Optical and Magnetic properties of the samples were investigated by X-ray diffraction (XRD), UV-VIS-NIR spectroscopy and VSM. Fluorite structure is confirmed from the XRD measurement on Gd doped CeO2 samples. Magnetic studies showed that the Gd doped polycrystalline samples display room temperature ferromagnetism and the ferromagnetic ordering strengthens with the Gd concentration.

  15. Mechanisms of enhanced sulfur tolerance on samarium (Sm)-doped cerium oxide (CeO2) from first principles.

    PubMed

    Lim, Dong-Hee; Kim, Hee Su; Yoon, Sung Pil; Han, Jonghee; Yoon, Chang Won; Choi, Sun Hee; Nam, Suk Woo; Ham, Hyung Chul

    2014-06-14

    The role of samarium (Sm) 4f states and Sm-perturbed O 2p states in determining the sulfur tolerance of Sm-doped CeO2 was elucidated by using the density functional theory (DFT) + U calculation. We find that the sulfur tolerance of Sm-doped CeO2 is closely related to the modification of O 2p states by the strong interaction between Sm 4f and O 2p states. In particular, the availability of unoccupied O 2p states near the Fermi level is responsible for enhancing the sulfur tolerance of Sm-doped CeO2 compared to the pure CeO2 by increasing the activity of the surface lattice oxygen toward sulfur adsorption, by weakening the interaction between Sm-O, and by increasing the migration tendency of the subsurface oxygen ion toward the surface.

  16. The synthesis of CeO2 nanospheres with different hollowness and size induced by copper doping

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Liu, Xiufang; Feng, Lijun; Guo, Jinxin; Xie, Anran; Wang, Shuping; Zhang, Jingcai; Yang, Yanzhao

    2014-08-01

    In this paper, copper-doped ceria oxides with different hollowness and size are fabricated by changing the Cu2+ doping concentration in the mixed water-glycol system. Results show that the copper-doped CeO2 oxides undergo a morphology transformation from the solid nanospheres to core-shell, then to hollow nanospheres with the increase of the Cu2+ doping concentration. The corresponding size becomes smaller during this transfer process. The Cu2+ doping induced acceleration in the nucleation and growth process is further investigated. The resultant Cu2+-doped CeO2 oxides exhibit enhanced CO conversion performance and better reduction behaviors.In this paper, copper-doped ceria oxides with different hollowness and size are fabricated by changing the Cu2+ doping concentration in the mixed water-glycol system. Results show that the copper-doped CeO2 oxides undergo a morphology transformation from the solid nanospheres to core-shell, then to hollow nanospheres with the increase of the Cu2+ doping concentration. The corresponding size becomes smaller during this transfer process. The Cu2+ doping induced acceleration in the nucleation and growth process is further investigated. The resultant Cu2+-doped CeO2 oxides exhibit enhanced CO conversion performance and better reduction behaviors. Electronic supplementary information (ESI) available: Fig. S1 the TEM images of the Cu2+-doped CeO2 (a-c): P2, P5 and P6; Fig. S2 EDS spectrum of the Cu2+-doped ceria sample; Fig. S3 the HRTEM images about lattice fringes of the Cu2+-doped CeO2: (a and b) P3; (c and d) P4; Fig. S4 the corresponding XPS survey spectrum of nanospheres: P1 and P4; Fig. S5 XRD pattern of P3 obtained at different solvothermal time, illustrated as (a) 1 h, (b) 2 h, (c) 4 h and (d) 8 h; Fig. S6 the TEM images of (a) the P1 sample at 36 h and (b) the P4 sample at 2 h; Fig. S7 N2 adsorption-desorption isotherms of the pure and Cu2+ doped CeO2: (a) P1, (b) P2, (c) P3, (d) P4, (e) P5 and (f) P6. Insets are the

  17. Catalytic propane reforming mechanism over Mn-Doped CeO2 (111)

    NASA Astrophysics Data System (ADS)

    Krcha, Matthew D.; Janik, Michael J.

    2015-10-01

    MnOx/CeOx mixed oxide systems exhibit encouraging hydrocarbon oxidation activity, without the inclusion of a noble metal. Using density functional theory (DFT) methods, we examined the oxidative reforming path of propane over the Mn-doped CeO2 (1 1 1) surface. A plausible set of elementary reaction steps are identified for conversion of propane to CO/CO2 and H2/H2O over the oxide surface. The rate-limiting reaction process may vary with redox conditions, with C-H dissociation limiting under more oxidizing conditions and more complex reaction sequences, including surface re-oxidation, limiting under highly reducing conditions. The possibility of intermediate desorption from the surface during the reforming process is low, with desorption energies of the intermediates being much less favorable than further surface reactions until CO/CO2 products are formed. The reforming paths over Mn-doped ceria are similar to those previously identified over Zr-doped ceria. The extent of surface reduction and the electronic structure of the surface intermediates are examined.

  18. Mg Doping Induced Effects on Structural, Optical, and Electrical Properties as Well as Cytotoxicity of CeO2 Nanostructures

    NASA Astrophysics Data System (ADS)

    Iqbal, Javed; Jan, Tariq; Awan, M. S.; Naqvi, Sajjad Haider; Badshah, Noor; ullah, Asmat; Abbas, Fazzal

    2016-04-01

    Here, Mg x Ce1- x O2 (where x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) nanostructures have been successfully synthesized by using a simple, easy, and cost-effective soft chemical method. X-ray diffraction (XRD) patterns substantiate the single-phase formation of a CeO2 cubic fluorite structure for all samples. Infrared spectroscopy results depict the presence of peaks only related to Ce-O bonding, which confirms the XRD results. It has been observed via ultraviolet (UV)-visible spectroscopy that Mg doping has tuned the optical band gap of CeO2 significantly. The electrical conductivity of CeO2 nanostructures has been found to increase with Mg doping, which is attributed to enhancement in carrier concentration due to the different valance states of dopant and host ions. Selective cytotoxic behavior of Mg x Ce1- x O2 nanostructures has been determined for neuroblastoma (SH-SY5Y) cancerous and HEK-293 healthy cells. Both doped and undoped CeO2 nanostructures have been found to be toxic for cancer cells and safe toward healthy cells. This selective toxic behavior of the synthesized nanostructures has been assigned to the different levels of reactive oxygen species (ROS) generation in different types of cells. This makes the synthesized nanostructures a potential option for cancer therapy in the near future.

  19. Effect of Doping on Surface Reactivity and Conduction Mechanism in Sm-doped CeO2 Thin Films

    DOE PAGESBeta

    Yang, Nan; Belianinov, Alex; Strelcov, Evgheni; Tebano, Antonello; Daniele, Di Castro; Schlueter, Christoph; Lee, Tien-Lin; Baddorf, Arthur P.; Wisinger, Nina; Jesse, Stephen; et al

    2014-11-21

    Scanning probe microscopy measurements show irreversible surface electrochemistry in Sm-doped CeO2 thin films, which depends on humidity, temperature and doping concentration. A systematic study by electrochemical strain microscopy (ESM) in samples with two different Sm content and in several working conditions allows disclosing the microscopic mechanism underlying the difference in water adsorption and splitting with subsequent proton liberation. We measure the behavior of the hysteresis loops by changing temperature and humidity, both in standard ESM configuration and using the first order reversal curve (FORC) method. Complementing our study with spectroscopic measurements by hard x-ray photoemission spectroscopy we find that watermore » incorporation is favored until the doping with Sm is too high to allow the presence of Ce3+. The influence of doping on the surface reactivity and conduction mechanism clearly emerges from all of our experimental results. We find that at lower Sm concentration proton conduction is prevalent, featured by lower activation energy and higher mobility. Defect concentrations determine the type of the prevalent charge carrier in a doping dependent manner.« less

  20. Effect of Doping on Surface Reactivity and Conduction Mechanism in Sm-doped CeO2 Thin Films

    SciTech Connect

    Yang, Nan; Belianinov, Alex; Strelcov, Evgheni; Tebano, Antonello; Daniele, Di Castro; Schlueter, Christoph; Lee, Tien-Lin; Baddorf, Arthur P.; Wisinger, Nina; Jesse, Stephen; Kalinin, Sergei V; Balestrino, Giuseppe; Aruta, Carmela

    2014-11-21

    Scanning probe microscopy measurements show irreversible surface electrochemistry in Sm-doped CeO2 thin films, which depends on humidity, temperature and doping concentration. A systematic study by electrochemical strain microscopy (ESM) in samples with two different Sm content and in several working conditions allows disclosing the microscopic mechanism underlying the difference in water adsorption and splitting with subsequent proton liberation. We measure the behavior of the hysteresis loops by changing temperature and humidity, both in standard ESM configuration and using the first order reversal curve (FORC) method. Complementing our study with spectroscopic measurements by hard x-ray photoemission spectroscopy we find that water incorporation is favored until the doping with Sm is too high to allow the presence of Ce3+. The influence of doping on the surface reactivity and conduction mechanism clearly emerges from all of our experimental results. We find that at lower Sm concentration proton conduction is prevalent, featured by lower activation energy and higher mobility. Defect concentrations determine the type of the prevalent charge carrier in a doping dependent manner.

  1. Strongly enhanced oxygen ion transport through samarium-doped CeO2 nanopillars in nanocomposite films

    DOE PAGESBeta

    Yang, Sangmo; Lee, Shinbuhm; Jian, Jie; Zhang, Wenrui; Lu, Ping; Jia, Quanxi; Wang, Haiyan; Noh, Tae Won; Kalinin, Sergei V.; MacManus-Driscoll, Judith L.

    2015-10-08

    Enhancement of oxygen ion conductivity in oxides is important for low-temperature (<500 °C) operation of solid oxide fuel cells, sensors and other ionotronic devices. While huge ion conductivity has been demonstrated in planar heterostructure films, there has been considerable debate over the origin of the conductivity enhancement, in part because of the difficulties of probing buried ion transport channels. Here we create a practical geometry for device miniaturization, consisting of highly crystalline micrometre-thick vertical nanocolumns of Sm-doped CeO2 embedded in supporting matrices of SrTiO3. The ionic conductivity is higher by one order of magnitude than plain Sm-doped CeO2 films. Bymore » using scanning probe microscopy, we show that the fast ion-conducting channels are not exclusively restricted to the interface but also are localized at the Sm-doped CeO2 nanopillars. This work offers a pathway to realize spatially localized fast ion transport in oxides of micrometre thickness.« less

  2. Strongly enhanced oxygen ion transport through samarium-doped CeO2 nanopillars in nanocomposite films.

    PubMed

    Yang, Sang Mo; Lee, Shinbuhm; Jian, Jie; Zhang, Wenrui; Lu, Ping; Jia, Quanxi; Wang, Haiyan; Noh, Tae Won; Kalinin, Sergei V; MacManus-Driscoll, Judith L

    2015-10-08

    Enhancement of oxygen ion conductivity in oxides is important for low-temperature (<500 °C) operation of solid oxide fuel cells, sensors and other ionotronic devices. While huge ion conductivity has been demonstrated in planar heterostructure films, there has been considerable debate over the origin of the conductivity enhancement, in part because of the difficulties of probing buried ion transport channels. Here we create a practical geometry for device miniaturization, consisting of highly crystalline micrometre-thick vertical nanocolumns of Sm-doped CeO2 embedded in supporting matrices of SrTiO3. The ionic conductivity is higher by one order of magnitude than plain Sm-doped CeO2 films. By using scanning probe microscopy, we show that the fast ion-conducting channels are not exclusively restricted to the interface but also are localized at the Sm-doped CeO2 nanopillars. This work offers a pathway to realize spatially localized fast ion transport in oxides of micrometre thickness.

  3. Strongly enhanced oxygen ion transport through samarium-doped CeO2 nanopillars in nanocomposite films.

    PubMed

    Yang, Sang Mo; Lee, Shinbuhm; Jian, Jie; Zhang, Wenrui; Lu, Ping; Jia, Quanxi; Wang, Haiyan; Noh, Tae Won; Kalinin, Sergei V; MacManus-Driscoll, Judith L

    2015-01-01

    Enhancement of oxygen ion conductivity in oxides is important for low-temperature (<500 °C) operation of solid oxide fuel cells, sensors and other ionotronic devices. While huge ion conductivity has been demonstrated in planar heterostructure films, there has been considerable debate over the origin of the conductivity enhancement, in part because of the difficulties of probing buried ion transport channels. Here we create a practical geometry for device miniaturization, consisting of highly crystalline micrometre-thick vertical nanocolumns of Sm-doped CeO2 embedded in supporting matrices of SrTiO3. The ionic conductivity is higher by one order of magnitude than plain Sm-doped CeO2 films. By using scanning probe microscopy, we show that the fast ion-conducting channels are not exclusively restricted to the interface but also are localized at the Sm-doped CeO2 nanopillars. This work offers a pathway to realize spatially localized fast ion transport in oxides of micrometre thickness. PMID:26446866

  4. Strongly enhanced oxygen ion transport through samarium-doped CeO2 nanopillars in nanocomposite films

    PubMed Central

    Yang, Sang Mo; Lee, Shinbuhm; Jian, Jie; Zhang, Wenrui; Lu, Ping; Jia, Quanxi; Wang, Haiyan; Won Noh, Tae; Kalinin, Sergei V.; MacManus-Driscoll, Judith L.

    2015-01-01

    Enhancement of oxygen ion conductivity in oxides is important for low-temperature (<500 °C) operation of solid oxide fuel cells, sensors and other ionotronic devices. While huge ion conductivity has been demonstrated in planar heterostructure films, there has been considerable debate over the origin of the conductivity enhancement, in part because of the difficulties of probing buried ion transport channels. Here we create a practical geometry for device miniaturization, consisting of highly crystalline micrometre-thick vertical nanocolumns of Sm-doped CeO2 embedded in supporting matrices of SrTiO3. The ionic conductivity is higher by one order of magnitude than plain Sm-doped CeO2 films. By using scanning probe microscopy, we show that the fast ion-conducting channels are not exclusively restricted to the interface but also are localized at the Sm-doped CeO2 nanopillars. This work offers a pathway to realize spatially localized fast ion transport in oxides of micrometre thickness. PMID:26446866

  5. NO reduction by CO over CuO supported on CeO2-doped TiO2: the effect of the amount of a few CeO2.

    PubMed

    Deng, Changshun; Li, Bin; Dong, Lihui; Zhang, Feiyue; Fan, Minguang; Jin, Guangzhou; Gao, Junbin; Gao, Liwen; Zhang, Fei; Zhou, Xinpeng

    2015-06-28

    This work is mainly focused on the investigation of the influence of the amount of a few CeO2 on the physicochemical and catalytic properties of CeO2-doped TiO2 catalysts for NO reduction by a CO model reaction. The obtained samples were characterized by means of XRD, N2-physisorption (BET), LRS, UV-vis DRS, XPS, (O2, CO, and NO)-TPD, H2-TPR, in situ FT-IR, and a NO + CO model reaction. These results indicate that a small quantity of CeO2 doping into the TiO2 support will cause an obvious change in the properties of the catalyst and the TC-60 : 1 (the TiO2/CeO2 molar ratio is 60 : 1) support exhibits the most extent of lattice expansion, which indicates that the band lengths of Ce-O-Ti are longer than other TC (the solid solution of TiO2 and CeO2) samples, probably contributing to larger structural distortion and disorder, more defects and oxygen vacancies. Copper oxide species supported on TC supports are much easier to be reduced than those supported on the pure TiO2 and CeO2 surface-modified TiO2 supports. Furthermore, the Cu/TC-60 : 1 catalyst shows the highest activity and selectivity due to more oxygen vacancies, higher mobility of surface and lattice oxygen at lower temperature (which contributes to the regeneration of oxygen vacancies, and the best reducing ability), the most content of Cu(+), and the strongest synergistic effect between Ti(3+), Ce(3+) and Cu(+). On the other hand, the CeO2 doping into TiO2 promotes the formation of a Cu(+)/Cu(0) redox cycle at high temperatures, which has a crucial effect on N2O reduction. Finally, in order to further understand the nature of the catalytic performances of these samples, taking the Cu/TC-60 : 1 catalyst as an example, a possible reaction mechanism is tentatively proposed.

  6. Yb,Er-doped CeO2 nanotubes as an assistant layer for photoconversion-enhanced dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Zhao, Rongfang; Huan, Long; Gu, Peng; Guo, Rong; Chen, Ming; Diao, Guowang

    2016-11-01

    Yb,Er-doped CeO2 nanotubes were successfully synthesized using Ag nanowires as a hard template via a facile hydrothermal reaction and subsequent calcination and leaching processes. Yb,Er-doped CeO2 nanotubes as a promising assistant layer were investigated to determine theirs photovoltaic properties in an effort to enhance the power conversion efficiency of dye-sensitized solar cells (DSSCs). The influence factors of photoelectric properties of CeO2:Yb,Er NTs, including diameter of nanotubes, hydrothermal time, calcination temperature, and elements doping, have been studied. Compared with pristine P25 photoanode, the DSSCs fabricated by CeO2:Yb,Er nanotubes and P25 exhibited a power conversion efficiency (η) of 8.67%, an increase of 34%, and incident photo-to-electric conversion efficiency (IPCE) of 92.96%, an increase of 48.83%, which evidence that CeO2:Yb,Er NTs are a promising assistant photoanode material for DSSCs. The enhance mechanism of CeO2:Yb,Er nanotubes has been further revealed according to experimental results.

  7. Identification of the arsenic resistance on MoO3 doped CeO2/TiO2 catalyst for selective catalytic reduction of NOx with ammonia.

    PubMed

    Li, Xiang; Li, Xiansheng; Li, Junhua; Hao, Jiming

    2016-11-15

    Arsenic resistance on MoO3 doped CeO2/TiO2 catalysts for selective catalytic reduction of NOx with NH3 (NH3-SCR) is investigated. It is found that the activity loss of CeO2-MoO3/TiO2 caused by As oxide is obvious less than that of CeO2/TiO2 catalysts. The fresh and poisoned catalysts are compared and analyzed using XRD, Raman, XPS, H2-TPR and in situ DRIFTS. The results manifest that the introduction of arsenic oxide to CeO2/TiO2 catalyst not only weakens BET surface area, surface acid sites and adsorbed NOx species, but also destroy the redox circle of Ce(4+) to Ce(3+) because of interaction between Ce and As. When MoO3 is added into CeO2/TiO2 system, the main SCR reaction path are found to be changed from the reaction between coordinated NH3 and ad-NOx species to that between an amide and gaseous NO. Additionally, for CeO2-MoO3/TiO2 catalyst, As toxic effect on active sites CeO2 can be released because of stronger As-Mo interaction. Moreover, not only are the reactable Brønsted and Lewis acid sites partly restored, but the cycle of Ce(4+) to Ce(3+) can also be free to some extent.

  8. Sm doped mesoporous CeO2 nanocrystals: aqueous solution-based surfactant assisted low temperature synthesis, characterization and their improved autocatalytic activity.

    PubMed

    Mandal, Bappaditya; Mondal, Aparna; Ray, Sirsendu Sekhar; Kundu, Amar

    2016-01-28

    Mesoporous Sm(3+) doped CeO2 (Ce-Sm) with a nanocrystalline framework, a high content of Ce(3+) and surface area (184 m(2) g(-1)), have been synthesized through a facile aqueous solution-based surfactant assisted route by using inorganic precursors and sodium dodecyl sulphate as a template. The XRD results indicate that the calcined Ce-Sm and even the as-prepared material have a cubic fluorite structure of CeO2 with no crystalline impurity phase. XRD studies along with HRTEM results confirmed the formation of mesoporous nanocrystalline CeO2 at a lower temperature as low as 100 °C. A detailed analysis revealed that Sm(3+) doping in CeO2 has increased the lattice volume, surface area, mesopore volume and engineered the surface defects. Higher concentrations of Ce(3+) and oxygen vacancies of Ce-Sm resulted in lowering of the band gap. It is evident from the H2-TPR results that Sm(3+) doping in CeO2 strongly modified the reduction behavior of CeO2 by shifting the bulk reduction at a much lower temperature, indicating increased oxygen mobility in the sample which enables enhanced oxygen diffusion at lower temperatures, thus promoting reducibility, i.e., the process of Ce(4+)→ Ce(3+). UV-visible transmission studies revealed improved autocatalytic performance due to easier Ce(4+)/Ce(3+) recycling in the Sm(3+) doped CeO2 nanoparticles. From the in vitro cytotoxicity of both pure CeO2 and Sm(3+) doped CeO2 calcined at 500 °C in a concentration as high as 100 μg mL(-1) (even after 120 h) on MG-63 cells, no obvious decrease in cell viability is observed, confirming their excellent biocompatibility. The presence of an increased amount of surface hydroxyl groups, mesoporosity, and surface defects have contributed towards an improved autocatalytic activity of mesoporous Ce-Sm, which appear to be a potential candidate for biomedical (antioxidant) applications.

  9. Identification of the arsenic resistance on MoO3 doped CeO2/TiO2 catalyst for selective catalytic reduction of NOx with ammonia.

    PubMed

    Li, Xiang; Li, Xiansheng; Li, Junhua; Hao, Jiming

    2016-11-15

    Arsenic resistance on MoO3 doped CeO2/TiO2 catalysts for selective catalytic reduction of NOx with NH3 (NH3-SCR) is investigated. It is found that the activity loss of CeO2-MoO3/TiO2 caused by As oxide is obvious less than that of CeO2/TiO2 catalysts. The fresh and poisoned catalysts are compared and analyzed using XRD, Raman, XPS, H2-TPR and in situ DRIFTS. The results manifest that the introduction of arsenic oxide to CeO2/TiO2 catalyst not only weakens BET surface area, surface acid sites and adsorbed NOx species, but also destroy the redox circle of Ce(4+) to Ce(3+) because of interaction between Ce and As. When MoO3 is added into CeO2/TiO2 system, the main SCR reaction path are found to be changed from the reaction between coordinated NH3 and ad-NOx species to that between an amide and gaseous NO. Additionally, for CeO2-MoO3/TiO2 catalyst, As toxic effect on active sites CeO2 can be released because of stronger As-Mo interaction. Moreover, not only are the reactable Brønsted and Lewis acid sites partly restored, but the cycle of Ce(4+) to Ce(3+) can also be free to some extent. PMID:27474851

  10. Enhancement of photocatalytic properties of TiO2 nanoparticles doped with CeO2 and supported on SiO2 for phenol degradation

    NASA Astrophysics Data System (ADS)

    Hao, Chunjing; Li, Jing; Zhang, Zailei; Ji, Yongjun; Zhan, Hanhui; Xiao, Fangxing; Wang, Dan; Liu, Bin; Su, Fabing

    2015-03-01

    A series of CeO2-TiO2 and CeO2-TiO2/SiO2 composites were prepared with TiCl4 and Ce (NO3)3·6H2O as precursors via a facile co-precipitation method. The obtained samples were characterized by various techniques such as X-ray diffraction (XRD), nitrogen adsorption (N2-BET), Fourier transformation infrared spectrum (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis spectroscopy measurements. The results indicated that TiO2 doped with CeO2 and supported on SiO2 could reduce the crystallite size, inhibit the phase transformation, enhance the thermal stability, and effectively extend the spectral response from UV to visible range. When applied to the phenol photodegradation on a homemade batch reactor with an external cooling jacket, the CeO2-TiO2/SiO2 catalysts exhibited significantly enhanced photodegradation efficiency in comparison with commercial Degussa P25 and CeO2-TiO2. The unique catalytic properties of CeO2-TiO2/SiO2 were ascribed to improved electron-hole pairs separation efficiency and formation of more reactive oxygen species owing to the presence of Ce3+/Ce4+, as well as high dispersion of active component of CeO2-TiO2 as a result of the introduction of SiO2 support. Furthermore, the catalysts can be easily recovered from the reaction solution by centrifugation and reused for four cycles without significant loss of activity.

  11. A DFT+U study on the contribution of 4f electrons to oxygen vacancy formation and migration in Ln-doped CeO2.

    PubMed

    Alaydrus, M; Sakaue, M; Kasai, H

    2016-05-14

    A rare earth doped form of ceria (CeO2) is of interest as a potential candidate for solid oxide fuel cells (SOFCs) because of its relatively high oxygen ion conductivity at temperatures below 600 °C. At the present time, computational chemistry has reached a certain maturity which allows the prediction of materials properties that are difficult to observe experimentally. However, understanding of the roles of dopants in the oxygen ion conduction in CeO2 is still incomplete for quantitatively reliable analysis due to the strong electron correlation of 4f electrons. In this study, density functional theory calculations with Hubbard U corrections are used to discuss ionic/covalent interactions in rare-earth-doped CeO2 and their consequences to oxygen ion conduction. This study suggests that the variable occupancy of empty 4f orbitals is important typically for early Ln elements to produce the covalent interactions that essentially affect the formation and migration of oxygen vacancies. This finding is important in understanding the factors responsible for oxygen ion diffusion in doped CeO2.

  12. Ferromagnetism in diluted magnetic Zn-Co-doped CeO2-δ

    NASA Astrophysics Data System (ADS)

    Santos, T. S.; Folly, W. S. D.; Macêdo, M. A.

    2012-08-01

    Several oxides doped with transition metals can be used in spintronics devices due to their conductive and magnetic properties at room temperature. In this work, samples of Ce1-2xZnxCoxO2-δ were obtained by an alternative sol-gel proteic process for x=0.01, 0.05 and 0.1. The structural properties of samples were analyzed by XRD and Raman spectroscopy. Magnetization measurements revealed a ferromagnetic behavior at room temperature probably induced by oxygen vacancies.

  13. Photon management properties of rare-earth (Nd,Yb,Sm)-doped CeO2 films prepared by pulsed laser deposition.

    PubMed

    Balestrieri, Matteo; Colis, Silviu; Gallart, Mathieu; Schmerber, Guy; Bazylewski, Paul; Chang, Gap Soo; Ziegler, Marc; Gilliot, Pierre; Slaoui, Abdelilah; Dinia, Aziz

    2016-01-28

    CeO2 is a promising material for applications in optoelectronics and photovoltaics due to its large band gap and values of the refractive index and lattice parameters, which are suitable for silicon-based devices. In this study, we show that trivalent Sm, Nd and Yb ions can be successfully inserted and optically activated in CeO2 films grown at a relatively low deposition temperature (400 °C), which is compatible with inorganic photovoltaics. CeO2 thin films can therefore be efficiently functionalized with photon-management properties by doping with trivalent rare earth (RE) ions. Structural and optical analyses provide details of the electronic level structure of the films and of their energy transfer mechanisms. In particular, we give evidence of the existence of an absorption band centered at 350 nm from which energy transfer to rare earth ions occurs. The transfer mechanisms can be completely explained only by considering the spontaneous migration of Ce(3+) ions in CeO2 at a short distance from the RE(3+) ions. The strong absorption cross section of the f-d transitions in Ce(3+) ions efficiently intercepts the UV photons of the solar spectrum and therefore strongly increases the potential of these layers as downshifters and downconverters.

  14. Hydrocracking of cumene over Ni/Al 2O 3 as influenced by CeO 2 doping and γ-irradiation

    NASA Astrophysics Data System (ADS)

    El-Shobaky, G. A.; Doheim, M. M.; Ghozza, A. M.

    2004-01-01

    Cumene hydrocracking was carried out over pure and doped Ni/Al 2O 3 solids and also, on these solids after exposure to different doses of γ-rays between 0.4 and 1.6 MGy. The dopant concentration was varied between 1 and 4 mol% CeO 2. Pure and doped samples were subjected to heat treatment at 400°C and cumene hydrocracking reaction was carried out using various solids at temperatures between 250°C and 400°C by means of micropulse technique. The results showed that both CeO 2 doping and γ-irradiation of the investigated system brought about an increase in its specific surface area. γ-irradiation of pure samples increased their catalytic activities effectively. However, the doping caused a decrease in the catalytic activity. γ-irradiation of the doped samples brought about a net decrease in the catalytic activity. The catalytic reaction products over different investigated solids were ethylbenzene as a major product together with different amounts of toluene, benzene and C 1-C 3 gaseous hydrocarbons. The selectivity towards the formation of various reaction products varies with the reaction temperature, doping and γ-irradiation.

  15. Surface morphology, optical and electrochemical properties of undoped and Ni-doped CeO2 thin films prepared by polymeric precursor method

    NASA Astrophysics Data System (ADS)

    Khosousi Sani, Zara; Esmaeli Ghodsi, Farhad; Mazloom, Jamal

    2016-04-01

    In this study, undoped and Ni-doped CeO2 thin films were deposited onto glass and ITO substrates by polymeric precursor (Pechini) method. Grazing incidence X-ray diffraction analysis revealed that the ceria thin film has a cerianite structure with the average crystallite size of 14 nm while the doped samples are amorphous. X-ray photoelectron spectroscopy (XPS) confirmed the presence of predominant Ce4+ oxidation state of ceria and Ni2+ in the films. Scanning electron microscopy (SEM) micrographs showed that the surface texture is crack free and the CeO2 grains regularly distributed on the surface. Optical constant (refractive index and extinction coefficient) and thickness of films were calculated using pointwise unconstraint minimization approach. The optical transmittance increases and the absorption edge has a blue shift by Ni incorporation. The highest band gap value (i.e., 3.43 eV) was obtained for 2.5 mol.% Ni doping sample. The refractive index and extinction coefficient of ceria films were decreased by Ni doping. The evaluated thicknesses are in the range of 150-170 nm. The strength of interband transition was appraised as a function of nickel content by using dielectric function. Luminescent emission intensity of the ceria film was enhanced by Ni doping. Cyclic voltammetry (CV) measurement revealed that the total charge density and ion storage capacitance of ceria thin film were increased by Ni doping.

  16. Near-infrared emissions from Yb3+-doped CeO2 and Ce2Si2O7 films based on silicon substrates subjected to thermal treatment

    NASA Astrophysics Data System (ADS)

    Mu, Guangyao; Wang, Shenwei; Li, Ling; Yin, Xue; Huang, Miaoling; Yi, Lixin

    2016-05-01

    Photoluminescence properties of Yb3+-doped CeO2 films annealed in different atmospheres were investigated. CeO2:Yb3+ films were deposited by electron-beam evaporation technique. Near-infrared emission around 970 nm was observed after annealing the films both in air and in Ar-H2 atmosphere, which is attributed to the Yb3+:2F5/2 → 2F7/2 transition. Optimization of the Yb3+ concentration for the 970 nm luminescence yield was also investigated. Characterized by different methods, Ce2Si2O7 was formed in the films annealed in reducing atmosphere, which was expected to be more applicable for the silicon-based optoelectronic applications.

  17. CeO2 doped anatase TiO2 with exposed (001) high energy facets and its performance in selective catalytic reduction of NO by NH3

    NASA Astrophysics Data System (ADS)

    Wang, Haiqiang; Cao, Shuang; Fang, Zheng; Yu, Feixiang; Liu, Yue; Weng, Xiaole; Wu, Zhongbiao

    2015-03-01

    Ceria doped on anatase TiO2 with high energy (001) facets was synthesized in this paper, which was subsequently utilized for selective catalytic reduction (SCR) of NO by NH3. After subjected to a range of analytical techniques, such as XRD, BET, TEM, XPS ESR, H2-TPR and NH3-TPD, it was found that compared with Ce/P25 catalyst, the presence of (001) facets over the TiO2 support had yielded a remarkably high activity at 390-490 °C for NO removal. The unique feature of active-energy (001) facets had enhanced the thermal stability of CeO2 whilst the presence of Ti3+ over the TiO2 surface had effectively facilitated the SCR process, both of which resulted in the remarkable catalytic performance for the catalyst.

  18. Interplay of dopant, defects and electronic structure in driving ferromagnetism in Co-doped oxides: TiO(2), CeO(2) and ZnO.

    PubMed

    Ali, Bakhtyar; Shah, Lubna R; Ni, C; Xiao, J Q; Shah, S Ismat

    2009-11-11

    A comprehensive study of the defects and impurity (Co)-driven ferromagnetism is undertaken in the oxide semiconductors: TiO(2), ZnO and CeO(2). The effect of magnetic (Co(2+)) and non-magnetic (Cu(2+)) impurities in conjunction with defects, such as oxygen vacancies (V(o)), have been thoroughly investigated. Analyses of the x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) data reveal the incorporation of cobalt in the lattice, with no signature of cobalt segregation. It is shown that oxygen vacancies are necessary for the ferromagnetic coupling in the Co-doped oxides mentioned above. The possible exchange mechanisms responsible for the ferromagnetism are discussed in light of the energy levels of dopants in the host oxides. In addition, Co and Cu co-doped TiO(2) samples are studied in order to understand the role of point defects in establishing room temperature ferromagnetism. The parameters calculated from the bound magnetic polaron (BMP) and Jorgensen's optical electronegativity models offer a satisfactory explanation of the defect-driven ferromagnetism in the doped/co-doped samples.

  19. Dielectric and piezoelectric properties of CeO2-added nonstoichiometric (Na0.5K0.5)0.97(Nb0.96Sb0.04)O3 ceramics for piezoelectric energy harvesting device applications.

    PubMed

    Oh, Youngkwang; Noh, Jungrae; Yoo, Juhyun; Kang, Jinhee; Hwang, Larkhoon; Hong, Jaeil

    2011-09-01

    In this study, nonstoichiometric (Na(0.5)K(0.5))(0.97)(Nb(0.96)Sb(0.04))O(3) ceramics were fabricated and their dielectric and piezoelectric properties were investigated according to the CeO(2) addition. In this ceramic composition, CeO(2) addition improved sinterability, electromechanical coupling factor k(p), mechanical quality factor Q(m), piezoelectric constant d(33), and g(33). At the sintering temperature of 1100°C, for the 0.2wt% CeO(2) added specimen, the optimum values of density = 4.359 g/cm(3), k(p) = 0.443, Q(m) = 588, ε(r) = 444, d(33) = 159 pC/N, and g(33) = 35 × 10(-3) V·m/N, were obtained. A piezoelectric energy harvesting device using 0.2 wt% CeO(2)- added lead-free (K(0.5)Na(0.5))(0.97)(Nb(0.96)Sb(0.04))O(3) ceramics and a rectifying circuit for energy harvesting were fabricated and their electrical characteristics were investigated. Under an external vibration acceleration of 0.7 g, when the mass, the frequency of vibration generator, and matching load resistance were 2.4 g, 70 Hz, and 721 Ω, respectively, output voltage and power of piezoelectric harvesting device indicated the optimum values of 24.6 mV(rms) and 0.839 μW, respectively-suitable for application as the electric power source of a ubiquitous sensor network (USN) sensor node. PMID:21937318

  20. An ultrasensitive electrochemical sensor for simultaneous determination of xanthine, hypoxanthine and uric acid based on Co doped CeO2 nanoparticles.

    PubMed

    Lavanya, N; Sekar, C; Murugan, R; Ravi, G

    2016-08-01

    A novel electrochemical sensor has been fabricated using Co doped CeO2 nanoparticles for selective and simultaneous determination of xanthine (XA), hypoxanthine (HXA) and uric acid (UA) in a phosphate buffer solution (PBS, pH5.0) for the first time. The Co-CeO2 NPs have been prepared by microwave irradiation method and characterized by Powder XRD, Raman spectroscopy, HRTEM and VSM measurements. The electrochemical behaviours of XA, HXA and UA at the Co-CeO2 NPs modified glassy carbon electrode (GCE) were studied by cyclic voltammetry and square wave voltammetry methods. The modified electrode exhibited remarkably well-separated anodic peaks corresponding to the oxidation of XA, HXA and UA over the concentration range of 0.1-1000, 1-600 and 1-2200μM with detection limits of 0.096, 0.36, and 0.12μM (S/N=3), respectively. For simultaneous detection by synchronous change of the concentrations of XA, HXA and UA, the linear responses were in the range of 1-400μM each with the detection limits of 0.47, 0.26, and 0.43μM (S/N=3), respectively. The fabricated sensor was further applied to the detection of XA, HXA and UA in human urine samples with good selectivity and high reproducibility.

  1. Chemical reaction mechanisms between Y2O3 stabilized ZrO2 and Gd doped CeO2 with PH3 in coal syngas

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Kishimoto, Haruo; Yamaji, Katsuhiko; Kuramoto, Koji; Gong, Mingyang; Liu, Xingbo; Hackett, Gregory; Gerdes, Kirk; Horita, Teruhisa

    2014-12-01

    To clarify the chemical stability of the key materials exposed to coal syngas (CSG) containing PH3 contaminant atmosphere, exposure tests of Y2O3 8 mol.% stabilized ZrO2 (YSZ) and Gd doped CeO2 (GDC) are carried out in simulated CSG with different concentrations of PH3. Significant reaction between YSZ and 10 ppm PH3 in CSG atmosphere is confirmed, and no obvious reaction is detected on the surface of YSZ after exposed in CSG with 1 ppm PH3. YPO4, Zr2.25(PO4)3 and monoclinic Y partial stabilized ZrO2 (m-PSZ) are identified on the YSZ pellet surface after exposed in CSG with 10 ppm PH3. GDC reacted with PH3 even at 1 ppm concentration. A (Ce0.9Gd0.1)PO4 layer is formed on the surface of GDC pellet after exposure in CSG with 10 ppm PH3. Possible reaction mechanisms between YSZ and GDC with PH3 in CSG are clarified. Compared with GDC, YSZ exhibits sufficient phosphorus resistance for devices directly exposed to a coal syngas atmosphere containing low concentration of PH3.

  2. Physico-Chemical Property and Catalytic Activity of a CeO2-Doped MnO(x)-TiO2 Catalyst with SO2 Resistance for Low-Temperature NH3-SCR of NO(x).

    PubMed

    Shin, Byeongkil; Chun, Ho Hwan; Cha, Jin-Sun; Shin, Min-Chul; Lee, Heesoo

    2016-05-01

    The effects of CeO2 addition on the catalytic activity and the SO2 resistance of CeO2-doped MnO(x)-TiO2 catalysts were investigated for the low-temperature selective catalytic reduction (SCR) with NH3 of NO(x) emissions in marine applications. The most active catalyst was obtained from 30 wt% CeO2-MnO(x)-TiO2 catalyst in the whole temperature range of 100-300 degrees C at a low gas hourly space velocity (GHSV) of 10,000 h(-)1, and its de-NO(x) efficiency was higher than 90% over 250 degrees C. The enhanced catalytic activity may contribute to the dispersion state and catalytic acidity on the catalyst surface, and the highly dispersed Mn and Ce on the nano-scaled TiO2 catalyst affects the increase of Lewis and Brønsted acid sites. A CeO2-rich additive on MnO(x)-TiO2 could provide stronger catalytic acid sites, associated with NH3 adsorption and the SCR performance. As the results of sulfur resistance in flue gas that contains SO2, the de-NO(x) efficiency of MnO(x)-TiO2 decreased by 15% over 200 degrees C, whereas that of 30 wt% ceria-doped catalyst increased by 14-21% over 150 degrees C. The high SO2 resistance of CeO2-MnO(x)-TiO2 catalysts that resulted from the addition of ceria suppressed the formation of Mn sulfate species, which led to deactivation on the surface of nano-catalyst. PMID:27483759

  3. Physico-Chemical Property and Catalytic Activity of a CeO2-Doped MnO(x)-TiO2 Catalyst with SO2 Resistance for Low-Temperature NH3-SCR of NO(x).

    PubMed

    Shin, Byeongkil; Chun, Ho Hwan; Cha, Jin-Sun; Shin, Min-Chul; Lee, Heesoo

    2016-05-01

    The effects of CeO2 addition on the catalytic activity and the SO2 resistance of CeO2-doped MnO(x)-TiO2 catalysts were investigated for the low-temperature selective catalytic reduction (SCR) with NH3 of NO(x) emissions in marine applications. The most active catalyst was obtained from 30 wt% CeO2-MnO(x)-TiO2 catalyst in the whole temperature range of 100-300 degrees C at a low gas hourly space velocity (GHSV) of 10,000 h(-)1, and its de-NO(x) efficiency was higher than 90% over 250 degrees C. The enhanced catalytic activity may contribute to the dispersion state and catalytic acidity on the catalyst surface, and the highly dispersed Mn and Ce on the nano-scaled TiO2 catalyst affects the increase of Lewis and Brønsted acid sites. A CeO2-rich additive on MnO(x)-TiO2 could provide stronger catalytic acid sites, associated with NH3 adsorption and the SCR performance. As the results of sulfur resistance in flue gas that contains SO2, the de-NO(x) efficiency of MnO(x)-TiO2 decreased by 15% over 200 degrees C, whereas that of 30 wt% ceria-doped catalyst increased by 14-21% over 150 degrees C. The high SO2 resistance of CeO2-MnO(x)-TiO2 catalysts that resulted from the addition of ceria suppressed the formation of Mn sulfate species, which led to deactivation on the surface of nano-catalyst.

  4. Properties of transparent Re3+: Y2O3 ceramics doped with tetravalent additives

    NASA Astrophysics Data System (ADS)

    Osipov, V. V.; Shitov, V. A.; Maksimov, R. N.; Solomonov, V. I.

    2015-12-01

    Neodymium or ytterbium-doped transparent yttrium oxide ceramics with different tetravalent sintering additives (ZrO2, HfO2, or CeO2) were fabricated from nanopowders produced by laser ablation method. Phase composition and distribution of dopants in the synthesized nanopowders and ceramics were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) spectroscopy. The tetravalent additives led to a decrease in grain size and an improvement in transmittance at the lasing wavelengths. However, an excess of tetravalent ions led to the formation of dispersed scattering volumes. We observed particles with modulated composition for nanopowder of Nd:Y2O3 doped by 10 mol% HfO2. The estimations based on Rayleigh light scattering showed that the maximum size of the dispersed scattering volume is below 20 nm.

  5. CO2 reforming of CH4 over CeO2-doped Ni/Al2O3 nanocatalyst treated by non-thermal plasma.

    PubMed

    Rahemi, Nader; Haghighi, Mohammad; Babaluo, Ali Akbar; Jafari, Mahdi Fallah; Estifaee, Pooya

    2013-07-01

    Ni/Al2O3 and Ni/Al2O3-CeO2 nanocatalysts have been prepared with impregnation method, treated with non-thermal plasma, characterized and tested for dry reforming of methane. For catalyst characterization, the following techniques have been used: XRD, FESEM, TEM, EDX dot mapping, BET, FTIR, TG-DTG, and XPS techniques. According to XRD and XPS, Ni in all catalysts exists as NiO and NiAl2O4 that existence of NiAl2O4 reveals strong interaction between active phase and support. Catalyst particles had smaller average particle size in plasma treated Ni/Al2O3-CeO2 nanocatalyst with less agglomeration. Homogenous dispersion of active phase, narrower particle size distribution, and uniform morphology has been observed in ceria containing plasma treated catalyst. The plasma treated Ni/Al2O3-CeO2 nanocatalyst showed bigger NiAl2O4/NiO ratio in XPS analysis that is indicative of stronger interaction between Ni and Al2O3 in the presence of CeO2. The dry reforming of methane was carried out at 550-850 degrees C using a mixture of CH4:CO2 (0.5:2). Improved morphology of the plasma treated Ni/Al2O3-CeO2 nanocatalyst, resulted from both CeO2 and plasma treatment, caused higher ability of catalyst in H2 and CO production. Product yield decreased at higher GHSVs, due to the fact that mass transport limitations will be more severe at low residence time, but this reduction would be less noticeable in the plasma treated Ni/Al2O3-CeO2 nanocatalyst. In addition, the plasma treated Ni/Al2O3-CeO2 nanocatalyst can keep the reactivity without deactivation for either CH4 or CO2 conversion better than other investigated catalysts.

  6. Effect of Ce doping of TiO2 support on NH3-SCR activity over V2O5-WO3/CeO2-TiO2 catalyst.

    PubMed

    Cheng, Kai; Liu, Jian; Zhang, Tao; Li, Jianmei; Zhao, Zhen; Wei, Yuechang; Jiang, Guiyuan; Duan, Aijun

    2014-10-01

    CeO2-TiO2 composite supports with different Ce/Ti molar ratios were prepared by a homogeneous precipitation method, and V2O5-WO3/CeO2-TiO2 catalysts for the selective catalytic reduction (SCR) of NOx with NH3 were prepared by an incipient-wetness impregnation method. These catalysts were characterized by means of BET, XRD, UV-Vis, Raman and XPS techniques. The results showed that the catalytic activity of V2O5-WO3/TiO2 was greatly enhanced by Ce doping (molar ratio of Ce/Ti=1/10) in the TiO2 support. The catalysts that were predominantly anatase TiO2 showed better catalytic performance than the catalysts that were predominantly fluorite CeO2. The Ce additive could enhance the surface adsorbed oxygen and accelerate the SCR reaction. The effects of O2 concentration, ratio of NH3/NO, space velocity and SO2 on the catalytic activity were also investigated. The presence of oxygen played an important role in NO reduction. The optimal ratio of NH3/NO was 1/1 and the catalyst had good resistance to SO2 poisoning. PMID:25288555

  7. Effect of Ce doping of TiO2 support on NH3-SCR activity over V2O5-WO3/CeO2-TiO2 catalyst.

    PubMed

    Cheng, Kai; Liu, Jian; Zhang, Tao; Li, Jianmei; Zhao, Zhen; Wei, Yuechang; Jiang, Guiyuan; Duan, Aijun

    2014-10-01

    CeO2-TiO2 composite supports with different Ce/Ti molar ratios were prepared by a homogeneous precipitation method, and V2O5-WO3/CeO2-TiO2 catalysts for the selective catalytic reduction (SCR) of NOx with NH3 were prepared by an incipient-wetness impregnation method. These catalysts were characterized by means of BET, XRD, UV-Vis, Raman and XPS techniques. The results showed that the catalytic activity of V2O5-WO3/TiO2 was greatly enhanced by Ce doping (molar ratio of Ce/Ti=1/10) in the TiO2 support. The catalysts that were predominantly anatase TiO2 showed better catalytic performance than the catalysts that were predominantly fluorite CeO2. The Ce additive could enhance the surface adsorbed oxygen and accelerate the SCR reaction. The effects of O2 concentration, ratio of NH3/NO, space velocity and SO2 on the catalytic activity were also investigated. The presence of oxygen played an important role in NO reduction. The optimal ratio of NH3/NO was 1/1 and the catalyst had good resistance to SO2 poisoning.

  8. Transparent Nd doped YAG ceramics

    NASA Astrophysics Data System (ADS)

    Stanciu, Catalina-Andreea; Dascalu, Traian; Stanciu, George; Pavel, Nicolaie

    2016-08-01

    The reasearch main objective is to obtain ceramic laser materials based on pure YAG (Y3Al5O12) and Nd doped YAG (Y3-xNdxAl5O12, with × = 0.5 and 1.0 at. %), by conventional solid state reaction method. Stoichiometric compositions of Y3Al5O12 (YAG), Y2.985Nd0.015Al5O12 (0.5 at.% Nd:YAG) and Y2.97Nd0.03Al5O12 (1.0 at.% Nd:YAG) were prepared using high purity Y2O3 (99.999%), Al2O3 (99.999%) and Nd2O3 (99.999%) nanopowders. Green bodies were sintered at 1750 °C for 16 h under vacuum (1.0 × 10-3 Pa) and then annealed at 1450 °C for 10 h in the air.

  9. All-solid-state electric-double-layer transistor based on oxide ion migration in Gd-doped CeO2 on SrTiO3 single crystal

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Takashi; Terabe, Kazuya; Aono, Masakazu

    2013-08-01

    An all-solid-state electric-double-layer transistor (EDLT) with a Gd-doped CeO2 (GDC) oxide ion conductor/SrTiO3 (STO) insulator structure has been developed. At 473 K, the drain current of the EDLT was well controlled, from less than nA order to μA order, by electrostatic carrier doping at the GDC/STO interface due to oxide ion (O2-) migration in the GDC, in contrast to an inactiveness at room temperature. The EDL capacitance at the interface, measured with an ac impedance spectroscopy, was 14 μF cm-2, higher than that reported for a microporous-SiO2 EDLT and comparable to that of an ionic-liquid-gated EDLT.

  10. Electrodeposited Biaxially Textured CeO2 and CeO2:Sm Buffer Layer for YBCO Superconductor Oxide Films

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Raghu; Phok, Sovannary; Spagnol, Priscila; Chaudhuri, Tapas

    2006-03-01

    Nonvacuum electrodeposition was used to prepare biaxially textured CeO2 and Sm-doped CeO2 coatings on Ni-W substrates. The samples were characterized by X-ray diffraction (including θ/2θ, pole figures, omega scans, and phi scans), atomic force microscopy (AFM), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Full-width at half-maximum values of the ω scan and φ scan of the electrodeposited layers were better than those of the Ni-W base substrates, indicating improved biaxial texturing of the electrodeposited layers.

  11. Surface electrochemistry of CO2 reduction and CO oxidation on Sm-doped CeO(2-x): coupling between Ce(3+) and carbonate adsorbates.

    PubMed

    Feng, Zhuoluo A; Machala, Michael L; Chueh, William C

    2015-05-14

    The efficient electro-reduction of CO2 to chemical fuels and the electro-oxidation of hydrocarbons for generating electricity are critical toward a carbon-neutral energy cycle. The simplest reactions involving carbon species in solid-oxide fuel cells and electrolyzer cells are CO oxidation and CO2 reduction, respectively. In catalyzing these reactions, doped ceria exhibits a mixed valence of Ce(3+) and Ce(4+), and has been employed as a highly active and coking-resistant electrode. Here we report an operando investigation of the surface reaction mechanism on a ceria-based electrochemical cell using ambient pressure X-ray photoelectron spectroscopy. We show that the reaction proceeds via a stable carbonate intermediate, the coverage of which is coupled to the surface Ce(3+) concentration. Under CO oxidation polarization, both the carbonate and surface Ce(3+) concentration decrease with overpotential. Under CO2 reduction polarization, on the other hand, the carbonate coverage saturates whereas the surface Ce(3+) concentration increases with overpotential. The evolution of these reaction intermediates was analyzed using a simplified two-electron reaction scheme. We propose that the strong adsorbate-adsorbate interaction explains the coverage-dependent reaction mechanism. These new insights into the surface electrochemistry of ceria shed light on the optimization strategies for better fuel cell electrocatalysts.

  12. Effect of CeO2 and Y2O3 on microstructure, bioactivity and degradability of laser cladding CaO-SiO2 coating on titanium alloy.

    PubMed

    Li, H C; Wang, D G; Chen, C Z; Weng, F

    2015-03-01

    To solve the lack of strength of bulk biomaterials for load-bearing applications and improve the bioactivity of titanium alloy (Ti-6Al-4V), CaO-SiO2 coatings on titanium alloy were fabricated by laser cladding technique. The effect of CeO2 and Y2O3 on microstructure and properties of laser cladding coating was analyzed. The cross-section microstructure of ceramic layer from top to bottom gradually changes from cellular-dendrite structure to compact cellular crystal. The addition of CeO2 or Y2O3 refines the microstructure of the ceramic layer in the upper and middle regions. The refining effect on the grain is related to the kinds of additives and their content. The coating is mainly composed of CaTiO3, CaO, α-Ca2(SiO4), SiO2 and TiO2. Y2O3 inhibits the formation of CaO. After soaking in simulated body fluid (SBF), the calcium phosphate layer is formed on the coating surface, indicating the coating has bioactivity. After soaking in Tris-HCl solution, the samples doped with CeO2 or Y2O3 present a lower weight loss, indicating the addition of CeO2 or Y2O3 improves the degradability of laser cladding sample.

  13. Effect of CeO2 and Y2O3 on microstructure, bioactivity and degradability of laser cladding CaO-SiO2 coating on titanium alloy.

    PubMed

    Li, H C; Wang, D G; Chen, C Z; Weng, F

    2015-03-01

    To solve the lack of strength of bulk biomaterials for load-bearing applications and improve the bioactivity of titanium alloy (Ti-6Al-4V), CaO-SiO2 coatings on titanium alloy were fabricated by laser cladding technique. The effect of CeO2 and Y2O3 on microstructure and properties of laser cladding coating was analyzed. The cross-section microstructure of ceramic layer from top to bottom gradually changes from cellular-dendrite structure to compact cellular crystal. The addition of CeO2 or Y2O3 refines the microstructure of the ceramic layer in the upper and middle regions. The refining effect on the grain is related to the kinds of additives and their content. The coating is mainly composed of CaTiO3, CaO, α-Ca2(SiO4), SiO2 and TiO2. Y2O3 inhibits the formation of CaO. After soaking in simulated body fluid (SBF), the calcium phosphate layer is formed on the coating surface, indicating the coating has bioactivity. After soaking in Tris-HCl solution, the samples doped with CeO2 or Y2O3 present a lower weight loss, indicating the addition of CeO2 or Y2O3 improves the degradability of laser cladding sample. PMID:25637793

  14. Collective magnetic response of CeO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Coey, Michael; Ackland, Karl; Venkatesan, Munuswamy; Sen, Siddhartha

    2016-07-01

    The magnetism of nanoparticles and thin films of wide-bandgap oxides that include no magnetic cations is an unsolved puzzle. Progress has been hampered by both the irreproducibility of much of the experimental data, and the lack of any generally accepted theoretical explanation. The characteristic signature is a virtually anhysteretic, temperature-independent magnetization curve that saturates in an applied field that is several orders of magnitude greater than the magnetization. It would seem as if a tiny volume fraction, <~0.1%, of the samples is magnetic and that the energy scale is unusually high for spin magnetism. Here we investigate the effect of dispersing 4 nm CeO2 nanoparticles with powders of γAl2O3, sugar or latex microspheres. The saturation magnetization, Ms ≍ 60 A m-1 for compact samples, is maximized by 1 wt% lanthanum doping. Dispersing the CeO2 nanopowder reduces its magnetic moment by up to an order of magnitude, and there is a characteristic length scale of order 100 nm for the magnetism to appear in CeO2 nanoparticle clusters. The phenomenon is explained in terms of a giant orbital paramagnetism that appears in coherent mesoscopic domains due to resonant interaction with zero-point fluctuations of the vacuum electromagnetic field. The theory explains the observed temperature-independent magnetization curve and its doping and dispersion dependence, based on a length scale of 300 nm that corresponds to the wavelength of a maximum in the ultraviolet absorption spectrum of the magnetic CeO2 nanoparticles. The coherent domains occupy roughly 10% of the sample volume.

  15. Synthesis of supported CeO2 nanofibers via electrospinning

    NASA Astrophysics Data System (ADS)

    Starbova, K.; Nihtianova, D.; Petrov, D.; Starbov, N.; Lovchinov, V.

    2012-12-01

    Fibrous CeO2 non-woven mats are synthesized via electrospinning. Homogeneous and stable aqueous polymer/cerium acetate blend spinning solutions are used. It is shown how the parameters of the solution, electrospinning, thermal post-processing can be successfully combined thus providing the synthesis of fibrous webs with mean diameters in the nanosized range. The morphologies of the samples are recorded under SEM and HRTEM while SAED is applied for studying their phase composition. The results obtained pave the way for the development of functional immobilized and self-supporting electrospun ceria ceramic materials.

  16. Nonlinear optical responses of erbium-doped YAG ceramics

    NASA Astrophysics Data System (ADS)

    Sun, Wangliang; Yi, Jun; Miao, Lili; Li, Jiang; Xie, Tengfei; Zhao, Chujun; Pan, Yubai; Wen, Shuangchun

    2016-07-01

    By performing the Z-scan measurements with ultrafast femtosecond laser centered at 800 nm wavelength, we can unambiguously distinguish the real and imaginary part of the third-order optical nonlinearity of the erbium-doped YAG ceramics. The reverse saturable absorption of the erbium-doped YAG ceramics has been observed experimentally, and the nonlinear refractive index of the ceramics is estimated to be about 10-21 m2/W. The experimental results may provide design guidelines for the high power laser design and its applications.

  17. Facet-Controlled CeO2 Nanocrystals for Oxidative Coupling of Methane.

    PubMed

    Sun, Yongnan; Shen, Yue; Song, Jianjun; Ba, Rongbin; Huang, Shuangshuang; Zhao, Yonghui; Zhang, Jun; Sun, Yuhan; Zhu, Yan

    2016-05-01

    Whether the catalysts of the high temperature reaction such methane oxidation coupling has a structure-sensitive catalytic behavior or not, it is discussed and confirmed the shape-specific impact on methane activity by designing the catalysts with different crystal facets exposed. CeO2 nanowires enclosed by {110} and {100} planes show the higher CH4 conversion and higher C2 hydrocarbons (C2H4 and C2H6) selectivity, compared with particle CeO2 rounded by {111} and {100} planes, suggesting that CeO2 (110) surface favors the activation of CH4. Encouraged by the result, to control facet-controlled synthesis of catalysts for tailoring the catalytic properties at high temperature, the CeO2 (110) surface is chosen as doped sites to form the doped catalyst such as Ca doped CeO2 nanowires for OCM reaction, enhancing C2 hydrocarbons selectivity dramatically and suppressing the deep oxidation product (CO and CO2) selectivity.

  18. Facet-Controlled CeO2 Nanocrystals for Oxidative Coupling of Methane.

    PubMed

    Sun, Yongnan; Shen, Yue; Song, Jianjun; Ba, Rongbin; Huang, Shuangshuang; Zhao, Yonghui; Zhang, Jun; Sun, Yuhan; Zhu, Yan

    2016-05-01

    Whether the catalysts of the high temperature reaction such methane oxidation coupling has a structure-sensitive catalytic behavior or not, it is discussed and confirmed the shape-specific impact on methane activity by designing the catalysts with different crystal facets exposed. CeO2 nanowires enclosed by {110} and {100} planes show the higher CH4 conversion and higher C2 hydrocarbons (C2H4 and C2H6) selectivity, compared with particle CeO2 rounded by {111} and {100} planes, suggesting that CeO2 (110) surface favors the activation of CH4. Encouraged by the result, to control facet-controlled synthesis of catalysts for tailoring the catalytic properties at high temperature, the CeO2 (110) surface is chosen as doped sites to form the doped catalyst such as Ca doped CeO2 nanowires for OCM reaction, enhancing C2 hydrocarbons selectivity dramatically and suppressing the deep oxidation product (CO and CO2) selectivity. PMID:27483809

  19. High permittivity in Zr doped NiO ceramics

    NASA Astrophysics Data System (ADS)

    Chen, K.; Yuan, S. K.; Li, P. L.; Gao, F.; Liu, J.; Li, G. L.; Zhao, A. G.; Lu, X. M.; Liu, J. M.; Zhu, J. S.

    2007-08-01

    We report on measurements of the dielectric permittivity of NiO-based ceramics doped with Zr (ZNO). Samples were prepared by the traditional solid-state reaction method. The concentration of Zr has an effect on the dielectric properties of ZNO ceramics. High permittivity values (˜104) were observed which remain almost constant from 200 K to 350 K at low frequencies. The high-dielectric-constant response of the ZNO ceramics is attributed mainly to a grain boundary (internal) barrier layer capacitance.

  20. Recent Progress in the Development of Neodymium Doped Ceramic Yttria

    NASA Technical Reports Server (NTRS)

    Prasad, Narasimha S.; Edwards, Chris; Trivedi, Sudhir B.; Kutcher, Susan; Wang, Chen-Chia; Kim, Joo-Soo; Hommerich, Uwe; Shukla, Vijay; Sadangi, Rajendra; Kear, Bernard

    2007-01-01

    Solid-state lasers play a significant role in providing the technology necessary for active remote sensing of the atmosphere. Neodymium doped yttria (Nd:Y2O3) is considered to be an attractive material due to its possible lasing wavelengths of aprrox.914 nm and approx.946 nm for ozone profiling. These wavelengths when frequency tripled can generate UV light at approx.305 nm and approx.315 nm, which is particularly useful for ozone sensing using differential absorption lidar technique. For practical realization of space based UV transmitter technology, ceramic Nd:Y2O3 material is considered to possess great potential. A plasma melting and quenching method has been developed to produce Nd3+ doped powders for consolidation into Nd:Y2O3 ceramic laser materials. This far-from-equilibrium processing methodology allows higher levels of rare earth doping than can be achieved by equilibrium methods. The method comprises of two main steps: (a) plasma melting and quenching to generate dense, and homogeneous doped metastable powders, (b) pressure assisted consolidation of these powders by hot isostatic pressing to make dense nanocomposite ceramics. Using this process, several 1" x 1" ceramic cylinders have been produced. The infrared transmission of undoped Y2O3 ceramics was as high as approx.75% without anti-reflection coating. In the case of Nd:Y2O3 ceramics infrared transmission values of approx.50% were achieved. Furthermore, Nd:Y2O3 samples with dopant concentrations of up to approx.2 at. % were prepared without significant emission quenching.

  1. Electrical properties of lanthanum doped barium titanate ceramics

    SciTech Connect

    Vijatovic Petrovic, M.M.; Bobic, J.D.; Ramoska, T.; Banys, J.; Stojanovic, B.D.

    2011-10-15

    Pure and lanthanum doped barium titanate (BT) ceramics were prepared by sintering pellets at 1300 deg. C for 8 h, obtained from nanopowders synthesized by the polymeric precursor method. XRD results showed formation of a tetragonal structure. The presence of dopants changed the tetragonal structure to pseudo-cubic. The polygonal grain size was reduced up to 300 nm with addition of lanthanum as a donor dopant. Determined dielectric properties revealed that lanthanum modified BT ceramics possessed a diffused ferroelectric character in comparison with pure BT that is a classical ferroelectric material. In doped BT phase transition temperatures were shifted to lower temperatures and dielectric constant values were much higher than in pure BT. A modified Currie Weiss law was used to explore the connection between the doping level and degree of diffuseness of phase transitions. Impedance spectroscopy measurements were carried out at different temperatures in order to investigate electrical resistivity of materials and appearance of a PTCR effect. - Highlights: {yields} Pure and lanthanum doped BaTiO{sub 3} were prepared by polymeric precursors method. {yields} Change of structure from tetragonal to pseudo-cubic. {yields} Lanthanum as a donor dopant influenced on change of ferro-para phase transition. {yields} The diffuseness factor indicated the formation of diffuse ferroelectric material. {yields} Lanthanum affected on PTCR effect appearance in BT ceramics.

  2. Luminescent properties of alumina ceramics doped with chromium oxide

    NASA Astrophysics Data System (ADS)

    Kortov, V.; Kiryakov, A.; Pustovarov, V.

    2016-08-01

    Ceramics doped with chromium oxide were synthesized from alumina nanopowder at high heating and cooling rates. XRD analysis of the obtained samples shows that they consist mainly of Al2O3 α-phase. Photoluminescence (PL) spectra in the visible spectral region and thermoluminescence (TL) curves were measured. An effect of the dopant concentration on the intensity and shape of the PL bands as well as on the TL yield was found. Annealing of the quenching defects which emerged during the synthesis changed the PL spectra. The centers responsible for PL and TL in the synthesized ceramics were identified.

  3. Spectroscopic characteristics of chromium doped mullite glass-ceramics

    SciTech Connect

    Wojtowicz, A.J.; Meng, W.; Lempicki, A.; Beall, G.H.; Hall, D.W.; Chin, T.C.

    1988-06-01

    Characteristics of chromium doped mullite ceramics are discussed with reference to possible laser applications. Dominant features are attributed to large and inherent spectroscopic inhomogeneity of mullite. The spectroscopic data are analyzed using a generalized McCumber theory. The peak stimulated emission cross section is 0.54 x 10/sup -20/ cm/sup 2/. This, together with preliminary single-pass measurements, indicate that gain for mullite is about 2.6 times smaller than gain for alexandrite.

  4. Promotion effects of SiO2 or/and Al2O3 doped CeO2/TiO2 catalysts for selective catalytic reduction of NO by NH3.

    PubMed

    Zhao, Wenru; Tang, Yu; Wan, Yaping; Li, Liang; Yao, Si; Li, Xiaowei; Gu, Jinlou; Li, Yongsheng; Shi, Jianlin

    2014-08-15

    A series of the CeO2-based catalysts loaded on TiO2, TiO2-SiO2, TiO2-Al2O3, and TiO2-SiO2-Al2O3 supports were prepared by incipient impregnation method for the selective catalytic reduction (SCR) of NO by NH3 in the presence of oxygen. The SCR activities of the catalysts with different supports increases in the order of Ce/TiO2 < Ce/TiO2-20SiO2 ≈ Ce/TiO2-3.5Al2O3 < Ce/TiO2-20SiO2-3.5Al2O3. The Ce/TiO2-20SiO2-3.5Al2O3 catalyst showed 100% NO conversion in the temperature range of 250-425°C and 100% N2 selectivity in the whole temperature range. The catalytic activity of Ce/TiO2-20SiO2-3.5Al2O3 exhibited good stability and strong resistance to SO2 and H2O poisoning. The co-introduction of SiO2 and Al2O3 into TiO2 could increase the amount of chemisorbed oxygen and Lewis acid sites on the surface of catalyst, which should be responsible for the excellent SCR activity.

  5. Spectroscopic properties of Nd3+ doped transparent oxyfluoride glass ceramics.

    PubMed

    Yu, Yunlong; Chen, Daqin; Ma, En; Wang, Yuansheng; Hu, Zhongjian

    2007-07-01

    In this paper, the spectroscopic properties of Nd(3+) doped transparent oxyfluoride glass ceramics containing LaF(3) nano-crystals were systematically studied. The formation and distribution of LaF(3) nano-crystals in the glass matrix were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on Judd-Ofelt theory, the intensity parameters Omega(t) (t=2, 4, 6), spontaneous emission probability, radiative lifetime, radiative quantum efficiency, width of the emission line and stimulated emission cross-section of Nd(3+) were evaluated. Particularly, the effect of Nd(3+) doping level on them was discussed. With the increase of Nd(3+) concentration in the glass ceramic, the experimental luminescence lifetime, radiative quantum efficiency and stimulated emission cross-section vary from 353.4 micros, 78.3% and 1.86 x 10(-20)cm(2) to 214.7 micros, 39.9% and 1.52 x 10(-20)cm(2), respectively. The comparative study of Nd(3+) spectroscopic parameters in different hosts suggests that the investigated glass ceramic system is potentially applicable as laser materials for 1.06 microm emission.

  6. Ytterbium-doped glass-ceramics for optical refrigeration.

    PubMed

    Filho, Elton Soares de Lima; Krishnaiah, Kummara Venkata; Ledemi, Yannick; Yu, Ye-Jin; Messaddeq, Younes; Nemova, Galina; Kashyap, Raman

    2015-02-23

    We report for the first time the characterization of glass-ceramics for optical refrigeration. Ytterbium-doped nanocrystallites were grown in an oxyfluoride glass matrix of composition 2YbF(3):30SiO(2)-15Al(2)O(3)-25CdF(2)-22PbF(2)-4YF(3), forming bulk glass-ceramics at three different crystalisation levels. The samples are compared with a corresponding uncrystalised (glass) sample, as well as a Yb:YAG sample which has presented optical cooling. The measured X-ray diffraction spectra, and thermal capacities of the samples are reported. We also report for the first time the use of Yb:YAG as a reference for absolute photometric quantum efficiency measurement, and use the same setup to characterize the glass and glass-ceramic samples. The cooling figure-of-merit was measured by optical calorimetry using a fiber Bragg grating and found to depend on the level of crystallization of the sample, and that samples with nanocrystallites result in higher quantum efficiency and lower background absorption than the pure-glass sample. In addition to laser-induced cooling, the glass-ceramics have the potential to serve as a reference for quantum efficiency measurements. PMID:25836500

  7. Structural and electrical characteristics of dysprosium-doped barium stannate titanate ceramics

    SciTech Connect

    Wang, Shijie; Tan, Tai Aik; Lai, Man On; Lu, Li

    2010-03-15

    Effects of dysprosium (Dy) amphoteric doping on the structural, dielectric and electric properties of barium stannate titanate (BTS) ceramics have been studied. X-ray diffraction analyses reveal that all Dy-doped BTS ceramics exhibit cubic perovskite structure until to 1 mol%. Dy doping at the A site shows lower solubility than that at the B site. SEM surface morphologies display that the Dy B site doping is beneficial for the compact and homogeneous grain distribution. The dielectric constant and loss tangent are reduced with increase of the doping levels. Impedance spectroscopy investigation demonstrates that all samples are insulating at room temperature. Doping alters the full resistive regions of pure BTS ceramics to Doped BTS with insulating grain boundaries and semiconducting bulk regions, but the doping contents has little effect on changing the electric structures.

  8. Fabrication and characterization of spark plasma sintered Ce:LuAG ceramic for scintillation application

    NASA Astrophysics Data System (ADS)

    Kumar, S. Arun; Senthilselvan, J.

    2016-05-01

    Rare earth Cerium doped Lutetium Aluminum Garnet (Ce:LuAG) ceramics are widely used as phosphor material in medical imaging and high-energy physics. Due to its technological importance, an attempt has been made to fabricate Ce:LuAG ceramics by using spark plasma sintering (SPS) technique. XRD patterns of SPS sintered Ce:LuAG ceramics reveals a mixed LuAG and CeO2 (antisite defect) phases. The microstructures of SPS sintered Ce:LuAG ceramics shows limited densification, inappropriate compaction of particles and existence of residual pores, voids between the grain boundaries affects the transparency of Ce:LuAG ceramics. Relative density and hardness of post sintered Ce:LuAG ceramic is also determined. The effect of Ce3+ doping concentration and sintering temperature on optical luminescence behavior of Ce:LuAG ceramic is presented.

  9. Spectroscopic characteristics of chromium-doped mullite glass-ceramics

    SciTech Connect

    Wojtowicz, A.J.; Meng, W.; Lempicki, A.; Beall, G.H.; Hall, D.W.

    1988-06-01

    The chromium (3+) ion has been widely used as an optical activator in solid-state, tunable laser materials. High octahedral field-stabilization energy and resistance against both oxidation and reduction minimize the dependence of chromium (3+) on the solid-state host matrix. However, the high sensitivity of electronic structure on crystal field strength makes the appropriate choice of host the condition for success. Characteristics of chromium-doped mullite ceramics are discussed with reference to possible laser applications. Dominant features are attributed to large and inherent spectroscopic inhomogeneity of mullite. The spectroscopic data are analyzed using a generalized McCumber theory. The peak-stimulated emission cross section is 0.54 x 10 to the -20 sq cm. This together with preliminary single-pass measurements, indicate that gain for mullite is about 2.6 times smaller than gain for alexandrite.

  10. Upconversion in erbium-doped transparent glass ceramics

    NASA Astrophysics Data System (ADS)

    Jones, Gina Christine

    2005-11-01

    Transparent glass ceramics (TGCs) are a class of materials that are composed of a robust glass matrix which is densely embedded with nanometer-sized fluoride crystals: In bulk, fluoride materials tend to have poor handling and mechanical properties, and can be expensive to produce. In contrast, the forming and handling properties of the TGC are similar to those of the precursor, glass, and are engineered to be robust and mechanically stable. Rare earth ions can be incorporated into the TGC during manufacture and can become partially segregated into the crystalline phase. There they experience the low-phonon energy environment of the fluoride nanocrystallite, which induces long energy level lifetimes and enhanced frequency upconversion. Therefore, rare earth doped TGCs can have the spectroscopic properties of a crystal with the durability of an aluminosilicate glass. Upconversion fluorescence is studied for an aluminosilicate TGC containing LaF3 nanocrystallites and doped with an erbium density of 1.7 x 1020 CM-3. Time gated fluorescence and excitation spectra as well as photoluminescence decays are used to find the nature and origin of this fluorescence. It is determined that energy transfer upconversion occurs only in the nanocrystallite phase and sequential two-photon absorption upconversion occurs in both glass and crystal phases.

  11. Ce-doped single crystal and ceramic garnets for γ ray detection

    SciTech Connect

    Hull, G; Roberts, J; Kuntz, J; Fisher, S; Sanner, R; Tillotson, T; Drobshoff, A; Payne, S; Cherepy, N

    2007-07-30

    Ceramic and single crystal Lutetium Aluminum Garnet scintillators exhibit energy resolution with bialkali photomultiplier tube detection as good as 8.6% at 662 keV. Ceramic fabrication allows production of garnets that cannot easily be grown as single crystals, such as Gadolinium Aluminum Garnet and Terbium Aluminum Garnet. Measured scintillation light yields of Cerium-doped ceramic garnets indicate prospects for high energy resolution.

  12. EPR of Gd3+ ion in mixed CeO2-Y2O3 nanocrystals

    NASA Astrophysics Data System (ADS)

    Aminov, L. K.; Kurkin, I. N.; Rakhmatullin, R. M.; Böttcher, R.; Pöppl, A.; Sen, S.

    2009-11-01

    This paper reports on the results of EPR studies of mixed CeO2-Y2O3 crystals (including nanosized crystals) doped by gadolinium ions. It is revealed that the width of the line corresponding to the allowed transition 1/2 ↔ -1/2 between the Kramers-conjugated states |±1/2> of the Gd3+ ion decreases with a decrease in the powder size from macrosizes to nanosizes. The observed dependence can be due to the increase in the unit cell size during grinding of the samples.

  13. Aluminum- and boron-co-doped ZnO ceramics: structural, morphological and electrical characterization

    NASA Astrophysics Data System (ADS)

    Liu, Shimin; Liu, Jindong; Jiang, Weiwei; Liu, Chaoqian; Ding, Wanyu; Wang, Hualin; Wang, Nan

    2016-10-01

    Highly dense and electrically conductive aluminum- and boron-co-doped ZnO (ABZO) ceramics were prepared by traditional pressureless sintering process. Single aluminum-doped ZnO (AZO) ceramics were synthesized with similar process and characterized for comparison. The densification behavior, crystal structure, morphology, composition and electrical properties of the ceramics were studied. Results indicated that AZO ceramics with the maximum relative density of 99.01 % were obtained only at 1350 °C for 4 h, which, however, was accompanied by electrical conductivity deterioration because of the increased insulated ZnAl2O4 phase formed in ceramics. Interestingly, the ABZO ceramics reached the maximum relative density of 98.84 % at 1100 °C, which was 250 °C lower compared with that of AZO ceramics. Moreover, the electrical conductivity of ABZO ceramics improved significantly with the increased sintering temperature and increased insulated ZnAl2O4 phase, which should be ascribed to the decreased grain boundaries and the resultant reduced carrier scattering in ceramics overcoming the influence of increased ZnAl2O4 phase due to boron doping effect.

  14. Lead-barium fluoroborate glass ceramics doped with Nd3+ or Er3+

    NASA Astrophysics Data System (ADS)

    Petrova, O. B.; Sevostjanova, T. S.; Anurova, M. O.; Khomyakov, A. V.

    2016-02-01

    Lead-barium fluoroborate glasses in the PbF2-BaF2-B2O3, PbF2-BaO-B2O3, and PbO- BaF2-B2O3 systems doped with rare-earth ions (Nd3+ or Er3+) are synthesized and studied. It is shown that, based on these glasses, it is possible to produce transparent glass ceramics with fluoride crystalline phases, including ceramics with one crystalline phase of the fluorite structure. The spectral and luminescent properties of the doped glasses, glass ceramics, and polycrystalline complex fluorides containing Pb, Ba, and rare ions are studied.

  15. Growth and optical properties of partially transparent Eu doped CaF{sub 2} ceramic

    SciTech Connect

    Ghosh, Manoranjan Sen, Shashwati Pitale, S. S. Goutam, U. K. Shinde, Seema Patra, G. D. Gadkari, S. C.

    2014-04-24

    Partially transparent ceramic of 2 at.% Eu doped CaF{sub 2} have been grown preferentially towards [111] direction. For this purpose, Eu doped CaF{sub 2} nanoparticles (size∼12 nm) obtained by a low temperature solution growth method has been pressed at 1000°C under vacuum. The preferentially grown ceramic shows 15% transparency within the visible range of spectrum. As confirmed by the X-ray diffraction result, the hot pressed ceramic exhibits reduced lattice volume than the nanopowder. It indicates Eu{sup 3+} as the dominant substituting ions at the Ca{sup 2+} sites of CaF{sub 2} lattice in the hot pressed ceramic material. It is corroborated by the photoluminescence results of hot pressed ceramic which shows strong red emission corresponding to Eu{sup 3+} sites. However, photoluminescence of nanopowder exhibits intense peak in the blue region of the spectrum which is characteristics of Eu2+ sites.

  16. CeO2 nanorods and gold nanocrystals supported on CeO2 nanorods as catalyst.

    PubMed

    Huang, P X; Wu, F; Zhu, B L; Gao, X P; Zhu, H Y; Yan, T Y; Huang, W P; Wu, S H; Song, D Y

    2005-10-20

    The formation mechanism of uniform CeO2 structure at the nanometer scale via a wet-chemical reaction is of great interest in fundamental study as well as a variety of applications. In this work, large-scale well-crystallized CeO2 nanorods with uniform diameters in the range of 20-30 nm and lengths up to tens of micrometers are first synthesized through a hydrothermal synthetic route in 5 M KOH solution at 180 degrees C for 45 h without any templates and surfactants. The nanorod formation involves dehydration of CeO2 nanoparticles and orientation growth along the 110 direction in KOH solution. Subsequently, gold nanoparticles with crystallite sizes between 10 and 20 nm are loaded on the surface of CeO2 nanorods using HAuCl4 solution as the gold source and NaBH4 solution as a reducing agent. The synthesized Au/CeO2 nanorods demonstrate a higher catalytic activity in CO oxidation than the pure CeO2 nanorods. PMID:16853472

  17. Effect of annealing temperature on the structural and optical properties of CeO2:Ni thin films

    NASA Astrophysics Data System (ADS)

    Murugan, R.; Vijayaprasath, G.; Sakthivel, P.; Mahalingam, T.; Ravi, G.

    2016-05-01

    High quality Ni-doped CeO2 (CeO2:Ni) thin films were deposited on glass substrates at room temperature by using radio frequency magnetron sputtering. The effect of annealing temperature on structural and optical properties of the CeO2:Ni films was investigated. The structural, optical and vibrational properties of the films were determined using X-ray diffraction (XRD), photoluminescence spectrometer (PL) and Raman spectrometer. It was found that the as-deposited film has a fluorite cubic structure. By increasing annealing temperature from 100°C to 300°C, the crystalline quality of the thin films could be improved. The UV and visible band emissions were observed in the photoluminescence spectra, due to exciton, defect related emissions respectively. The micro-Raman results show the characteristic peak of CeO2 F2g at 465 cm-1 and 2L0 at 1142 cm-1. Defect peaks like D and 0 bands were observed at 641 cm-1 and 548 cm-1 respectively. It is found from the spectra that the peak intensity of the films increased with increase of annealing temperature.

  18. Influence of rare earth doping on thermoelectric properties of SrTiO{sub 3} ceramics

    SciTech Connect

    Liu, J. Wang, C. L.; Li, Y.; Su, W. B.; Zhu, Y. H.; Li, J. C.; Mei, L. M.

    2013-12-14

    Thermoelectric properties of SrTiO{sub 3} ceramics, doped with different rare earth elements, were investigated in this work. It's found that the ionic radius of doping elements plays an important role on thermoelectric properties: SrTiO{sub 3} ceramics doped with large rare earth ions (such as La, Nd, and Sm) exhibit large power factors, and those doped with small ions (such as Gd, Dy, Er, and Y) exhibit low thermal conductivities. Therefore, a simple approach for enhancing the thermoelectric performance of SrTiO{sub 3} ceramics is proposed: mainly doped with large ions to obtain a large power factor and, simultaneously, slightly co-doped with small ions to obtain a low thermal conductivity. Based on this rule, Sr{sub 0.8}La{sub 0.18}Yb{sub 0.02}TiO{sub 3} ceramics were prepared, whose ZT value at 1 023 K reaches 0.31, increasing by a factor of 19% compared with the single-doped counterpart Sr{sub 0.8}La{sub 0.2}TiO{sub 3} (ZT = 0.26)

  19. Ultrafine Nanocrystalline CeO2@C-Containing NaAlH4 with Fast Kinetics and Good Reversibility for Hydrogen Storage.

    PubMed

    Zhang, Xin; Liu, Yongfeng; Wang, Ke; Li, You; Gao, Mingxia; Pan, Hongge

    2015-12-21

    A nanocrystalline CeO2@C-containing NaAlH4 composite is successfully synthesized in situ by hydrogenating a NaH-Al mixture doped with CeO2@C. Compared with NaAlH4 , the as-prepared CeO2@C-containing NaAlH4 composite, with a minor amount of excess Al, exhibits significantly improved hydrogen storage properties. The dehydrogenation onset temperature of the hydrogenated [NaH-Al-7 wt % CeO2@C]-0.04Al sample is 77 °C lower than that of the pristine sample because of a reduced kinetic barrier. More importantly, the dehydrogenated sample absorbs ∼4.7 wt % hydrogen within 35 min at 100°C and 10 MPa of hydrogen. Compositional and structural analyses reveal that CeO2 is converted to CeH2 during ball milling and that the newly formed CeH2 works with the excess of Al to synergistically improve the hydrogen storage properties of NaAlH4. Our findings will aid in the rational design of novel catalyst-doped complex hydride systems with low operating temperatures, fast kinetics, and long-term cyclability. PMID:26632764

  20. Ultrafine Nanocrystalline CeO2@C-Containing NaAlH4 with Fast Kinetics and Good Reversibility for Hydrogen Storage.

    PubMed

    Zhang, Xin; Liu, Yongfeng; Wang, Ke; Li, You; Gao, Mingxia; Pan, Hongge

    2015-12-21

    A nanocrystalline CeO2@C-containing NaAlH4 composite is successfully synthesized in situ by hydrogenating a NaH-Al mixture doped with CeO2@C. Compared with NaAlH4 , the as-prepared CeO2@C-containing NaAlH4 composite, with a minor amount of excess Al, exhibits significantly improved hydrogen storage properties. The dehydrogenation onset temperature of the hydrogenated [NaH-Al-7 wt % CeO2@C]-0.04Al sample is 77 °C lower than that of the pristine sample because of a reduced kinetic barrier. More importantly, the dehydrogenated sample absorbs ∼4.7 wt % hydrogen within 35 min at 100°C and 10 MPa of hydrogen. Compositional and structural analyses reveal that CeO2 is converted to CeH2 during ball milling and that the newly formed CeH2 works with the excess of Al to synergistically improve the hydrogen storage properties of NaAlH4. Our findings will aid in the rational design of novel catalyst-doped complex hydride systems with low operating temperatures, fast kinetics, and long-term cyclability.

  1. Defect Complex Effect in Nb Doped TiO2 Ceramics with Colossal Permittivity

    NASA Astrophysics Data System (ADS)

    Li, Fuchao; Shang, Baoqiang; Liang, Pengfei; Wei, Lingling; Yang, Zupei

    2016-10-01

    Donor-doped Nb x Ti1- x O2 ( x = 1%, 2%, 4%, 6%, and 8%) ceramics with giant permittivity (>104) and a very low dielectric loss (˜0.05) were sintered under flowing N2 at 1400°C for 10 h. By increasing Nb doping concentration, two different dielectric responses were evidenced in the frequency dependence of dielectric properties of Nb doped TiO2 ceramics, which corresponded to the space charge polarization and the electron-pinned defect-dipoles effect, respectively. Especially, combined with the x-ray photoelectron spectroscopy results, the electron-pinned defect-dipoles induced by the 2({Nb}^{5 + } )_{{Ti}}^{ bullet } to 4({Ti}^{3 + } )^'_{{Ti}} leftarrow {V}_{{o}}^{ bullet bullet } defect complex were further confirmed to give rise to both their high ɛr and low tan δ in the high frequency range for the Nb x Ti1- x O2 ceramics with x > 4%.

  2. Rare-earth doped transparent ceramics for spectral filtering and quantum information processing

    NASA Astrophysics Data System (ADS)

    Kunkel, Nathalie; Ferrier, Alban; Thiel, Charles W.; Ramírez, Mariola O.; Bausá, Luisa E.; Cone, Rufus L.; Ikesue, Akio; Goldner, Philippe

    2015-09-01

    Homogeneous linewidths below 10 kHz are reported for the first time in high-quality Eu3+ doped Y 2O3 transparent ceramics. This result is obtained on the 7F0→5D0 transition in Eu3+ doped Y 2O3 ceramics and corresponds to an improvement of nearly one order of magnitude compared to previously reported values in transparent ceramics. Furthermore, we observed spectral hole lifetimes of ˜15 min that are long enough to enable efficient optical pumping of the nuclear hyperfine levels. Additionally, different Eu3+ concentrations (up to 1.0%) were studied, resulting in an increase of up to a factor of three in the peak absorption coefficient. These results suggest that transparent ceramics can be useful in applications where narrow and deep spectral holes can be burned into highly absorbing lines, such as quantum information processing and spectral filtering.

  3. Oxygen vacancies versus fluorine at CeO2(111): a case of mistaken identity?

    PubMed

    Kullgren, J; Wolf, M J; Castleton, C W M; Mitev, P; Briels, W J; Hermansson, K

    2014-04-18

    We propose a resolution to the puzzle presented by the surface defects observed with STM at the (111) surface facet of CeO 2 single crystals. In the seminal paper of Esch et al. [Science 309, 752 (2005)] they were identified with oxygen vacancies, but the observed behavior of these defects is inconsistent with the results of density functional theory (DFT) studies of oxygen vacancies in the literature. We resolve these inconsistencies via DFT calculations of the properties of both oxygen vacancies and fluorine impurities at CeO2(111), the latter having recently been shown to exist in high concentrations in single crystals from a widely used commercial source of such samples. We find that the simulated filled-state STM images of surface-layer oxygen vacancies and fluorine impurities are essentially identical, which would render problematic their experimental distinction by such images alone. However, we find that our theoretical results for the most stable location, mobility, and tendency to cluster, of fluorine impurities are consistent with experimental observations, in contrast to those for oxygen vacancies. Based on these results, we propose that the surface defects observed in STM experiments on CeO2 single crystals reported heretofore were not oxygen vacancies, but fluorine impurities. Since the similarity of the simulated STM images of the two defects is due primarily to the relative energies of the 2p states of oxygen and fluorine ions, this confusion might also occur for other oxides which have been either doped or contaminated with fluorine.

  4. Resistance Measurements and Activation Energies Calculations of Pure and Platinum Doped Stannic Oxide Ceramics in Air

    SciTech Connect

    Ibrahim, Zuhairi; Othman, Zulkafli; Karim, Mohd Mustamam Abd; Holland, Diane

    2007-05-09

    Pure SnO2 and Pt-SnO2 ceramics were fabricated by the dry pressing method using a pressure of 40 Mpa and sintered at 1000 deg. C. Electrical resistance measurements were made using an impedance analyzer, in air and temperatures between 25 deg. C and 450 deg. C. The change in resistance in both pure and platinum-doped stannic oxide ceramics was discussed.

  5. Enhanced emissions in Tb3+-doped oxyfluoride scintillating glass ceramics containing BaF2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Huang, Lihui; Jia, Shijie; Li, Yang; Zhao, Shilong; Deng, Degang; Wang, Huanping; Jia, Guohua; Hua, Youjie; Xu, Shiqing

    2015-07-01

    Transparent Tb3+-doped glass ceramics containing BaF2 nanocrystals were prepared by melt-quenching method with subsequent heat treatment. The XRD and EDS results showed the precipitated crystalline phase in the glass matrix was BaF2. Under 376 nm light, Tb3+ doped oxyfluoride glass ceramics containing BaF2 nanocrystals showed more intense green emission than the as-made glass, and the emission intensity increased with increasing heat treatment temperature and time. The lifetimes of 541 nm emission of Tb3+ doped oxyfluoride glass ceramics were longer than that of as-made glass, which are in the range from 3.00 ms to 3.55 ms. Under X-ray excitation, the green emission was enhanced in the glass ceramics compared to the as-made glass. The results indicate Tb3+ doped oxyfluoride glass ceramics containing BaF2 nanocrystals could be a material candidate for X-ray glass scintillator for slow event detection.

  6. Microstructure and dielectric properties of (Nb + In) co-doped rutile TiO2 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Jinglei; Li, Fei; Zhuang, Yongyong; Jin, Li; Wang, Linghang; Wei, Xiaoyong; Xu, Zhuo; Zhang, Shujun

    2014-08-01

    The (Nb + In) co-doped TiO2 ceramics recently attracted considerable attention due to their colossal dielectric permittivity (CP) (˜100,000) and low dielectric loss (˜0.05). In this research, the 0.5 mol. % In-only, 0.5 mol. % Nb-only, and 0.5-7 mol. % (Nb + In) co-doped TiO2 ceramics were synthesized by standard conventional solid-state reaction method. Microstructure studies showed that all samples were in pure rutile phase. The Nb and In ions were homogeneously distributed in the grain and grain boundary. Impedance spectroscopy and I-V behavior analysis demonstrated that the ceramics may compose of semiconducting grains and insulating grain boundaries. The high conductivity of grain was associated with the reduction of Ti4+ ions to Ti3+ ions, while the migration of oxygen vacancy may account for the conductivity of grain boundary. The effects of annealing treatment and bias filed on electrical properties were investigated for co-doped TiO2 ceramics, where the electric behaviors of samples were found to be susceptible to the annealing treatment and bias field. The internal-barrier-layer-capacitance mechanism was used to explain the CP phenomenon, the effect of annealing treatment and nonlinear I-V behavior for co-doped rutile TiO2 ceramics. Compared with CaCu3Ti4O12 ceramics, the high activation energy of co-doped rutile TiO2 (3.05 eV for grain boundary) was thought to be responsible for the low dielectric loss.

  7. Distribution of Oxygen Vacancies and Gadolinium Dopants in ZrO2-CeO2 Multi-Layer Films Grown on α-Al2O3

    SciTech Connect

    Wang, Chong M.; Engelhard, Mark H.; Azad, Samina; Saraf, Laxmikant V.; McCready, David E.; Shutthanandan, V.; Yu, Zhongqing; Thevuthasan, Suntharampillai; Watanabe, M.; Williams, D. B.

    2006-06-15

    Gd-doped ZrO2 and CeO2 multi-layer films were deposited on α-Al2O3 (0001) using oxygen plasma assisted molecular beam epitaxy. Oxygen vacancies and Gd dopant distributions were investigated in these multi-layer films using x-ray diffraction (XRD), conventional and high-resolution transmission electron microscopy (HRTEM), annular dark-filed imaging in scanning transmission electron microscopy (STEM), energy dispersive x-ray spectroscopy (EDS) elemental mapping and x-ray photoelectron spectroscopy (XPS) depth profiling. EDS and XPS reveal that Gd concentration in the ZrO2 layer is lower than that in the CeO2 layer. As a result, higher oxygen vacancy concentration exists in CeO2 layers compared to that in ZrO2 layers. In addition, Gd is found to segregate only at the interfaces formed during the deposition of CeO2 layers on ZrO2 layers. On the other hand, the interfaces formed during the deposition of ZrO2 layers on CeO2 layers did not show any Gd segregation. The Gd segregation behavior at the every other interface is believed to be associated with the low solubility of Gd in ZrO2.

  8. Effect of Dysprosia Additive on the Consolidation of CeO2 by Spark Plasma Sintering

    SciTech Connect

    K. Choi; R. E. Reavis; D. D. Osterberg; B. J. Jacques; D. P. Butt; R. D. Mariani; D. E. Burkes; Z. A. Munir

    2012-05-01

    The influence of dysprosia addition on the sintering and resulting microstructure of nano-grained CeO2 ceramics was investigated as functions of the spark plasma sintering (SPS) parameters. The addition of Dy2O3 (forming a solid solution) resulted in an increase in relative density and a decrease in grain size. The relative density of samples with Dy2O3 content of 6 and 10 mol% was over 95% when sintered at 1050 C under 500 MPa for holding times as short as 5 minutes. The application of high pressure facilitated the consolidation to relatively high densities with minimal grain growth. Heating rate and holding time, however, had insignificant effect on density but a measurable effect on grain size.

  9. Unusual Compression Behavior of Nanocrystalline CeO2

    PubMed Central

    Wang, Qiming; He, Duanwei; Peng, Fang; Lei, Li; Liu, Pingping; Yin, Shuai; Wang, Pei; Xu, Chao; Liu, Jing

    2014-01-01

    The x-ray diffraction study of 12 nm CeO2 was carried out up to ~40 GPa using an angle dispersive synchrotron-radiation in a diamond-anvil cell with different pressure transmitting medium (PTM) (4:1 methanol: ethanol mixture, silicone oil and none) at room temperature. While the cubic fluorite-type structure CeO2 was retained to the highest pressure, there is progressive broadening and intensity reduction of the reflections with increasing pressure. At pressures above 12 GPa, an unusual change in the compression curve was detected in all experiments. Significantly, apparent negative volume compressibility was observed at P = 18–27 GPa with silicone oil as PTM, however it was not detected in other circumstances. The expansion of the unit cell volume of cubic CeO2 was about 1% at pressures of 15–27 GPa. To explain this abnormal phenomenon, a dual structure model (hard amorphous shell and relatively soft crystalline core) has been proposed. PMID:24658049

  10. Ho(3+)-doped nanophase glass ceramics for efficiency enhancement in silicon solar cells.

    PubMed

    Lahoz, Fernando

    2008-12-15

    Currently Er(3+)-doped fluorides are being used as upconversion phosphors to enhance the efficiency of Si solar cells, to our knowledge. However, this enhancement is strongly limited owing to the small solar spectral range around 1540 nm that is used. We demonstrate that Ho(3+)-doped oxyfluoride glass ceramics are adequate to enlarge the Si sub-bandgap region around 1170 nm that can be transformed into higher-energy photons, showing an upconversion efficiency 2 orders of magnitude higher than the precursor glass. As these materials are transparent at 1540 nm, they can be used complementarily with Er(3+)-doped phosphors for the same purpose.

  11. Doping and defect structure of mixed-conducting ceramics for gas separation

    NASA Astrophysics Data System (ADS)

    Zuo, Chendong

    , which is highest among all Ba(Zr0.8-xCexY0.2)O 3 (0.4≤x≤0.7) compositions. However, the relatively low electronic conductivity is not adequate for the hydrogen separation membrane to be used in a non-galvanic operation mode, electronic conduction must been introduced into the proton conductor to create mixed ionic-electronic conductors. Dense Ni-BZCY [Ni-Ba(Zr0.8-xCexY0.2)O 3-alpha] cermet composite membranes have been successfully fabricated for evaluating hydrogen permeability, and stability. Nickel phase enhances the hydrogen permeability of the ceramic phase by increasing the electronic conductivity of the composite, surface exchange kinetics, and improving mechanical stability. By comparing the BEI images of BZCY cermets with different Zirconium content, we can tell the grain size, shape and distribution of two phases are insensitive to the zirconium content. Doping Zirconium in the B-site only slightly reduced the hydrogen permeation at high temperatures (e.g. 900°C), but dramatically increased the chemical stability in CO2- and H2O-containing gases. The hydrogen permeation fluxes of Ni-BZCY cermet membrane increased with temperature for all the compositions and the flux decreased as the zirconium content increased at each fixed temperature, but they are comparable to that of Ni-BCY for the lower zirconium content samples (x=0.6, 0.7). While the hydrogen permeation flux through a Ni-BCY cermet membrane decreased sharply upon exposure to wet CO2 atmospheres, the hydrogen permeation flux of a Ni-BZCY was relatively stable for 80 h in atmospheres containing up to 30% CO2 at 900°C after a small initial decrease. Among the compositions studied (0.4≤x≤0.7), the Ni-BZCY7 (x=0.7) composition exhibited both highest H2 permeation rate and good chemistry stability, thus having potential for practical applications. The Ni-BZCY7 membrane was chose to further study based on the best overall performance. The hydrogen flux through a Ni-BZCY7 cermet membrane increased

  12. Cubic to tetragonal phase transition of Tm3+ doped nanocrystals in oxyfluoride glass ceramics

    NASA Astrophysics Data System (ADS)

    Li, Yiming; Zhao, Lijuan; Fu, Yuting; Shi, Yahui; Zhang, Xiaoyu; Yu, Hua

    2016-02-01

    Tm3+ ions doped β-PbF2 nanocrystals in oxyfluoride glass ceramics with different doping concentrations and thermal temperatures are prepared by a traditional melt-quenching and thermal treatment method to investigate the structure and the phase transition of Tm3+ doped nanocrystals. The structures are characterized by X-ray diffraction Rietveld analysis and confirmed with numerical simulation. The phase transitions are proved further by the emission spectra. Both of the doping concentration and thermal temperature can induce an Oh to D4h site symmetry distortion and a cubic to tetragonal phase transition. The luminescence of Tm3+ doped nanocrystals at 800 nm was modulated by the phase transition of the surrounding crystal field.

  13. Amorphization of ZrO2 + CeO2 Powders Through Mechanical Milling for the Use of Kinetic Spray

    NASA Astrophysics Data System (ADS)

    Li, Songlin; Wang, Lei; Xiong, Yuming; Bae, Gyuyeol; Lee, Changhee

    2013-12-01

    The coating formation in a kinetic spray process mainly depends on the impact of inflight particles at a high velocity. The plastic deformation at the impact interface would disrupt the native oxide scale on the particle and the substrate to generate the intimate contact of the atomic structures. Accordingly, it poses a challenge in producing ceramic coating during kinetic spray because of the lack of plasticity of ceramic powders at room temperature. In this study, we proposed to prepare ZrO2 ceramic coatings using partially amorphized powder with nanometer size in the kinetic spray process. To prepare the powder for the use of the kinetic spray, the amorphization and grain refinement of ZrO2 powder in mechanical ball milling were studied. The results showed that the amorphization and grain refinement were improved because of the formation of solid solution when the CeO2 agent was added. Subsequently, a nearly spherical powder was achieved via spray drying using the milled powders. The plasticity of the milled powders was tested in the kinetic spray process using Nitrogen as process gas. A dense ZrO2-CeO2 coating with a thickness of 50 μm was formed, whereas spraying milled ZrO2 powder can only lead to an inhomogeneous dispersion of the destructible particles on the surface of the substrate.

  14. Fabrication and characterization of Eu3+-doped Lu2O3 scintillation ceramics

    NASA Astrophysics Data System (ADS)

    Kopylov, Yu. L.; Kravchenko, V. B.; Dulina, N. A.; Lopin, А. V.; Parkhomenko, S. V.; Tolmachev, A. V.; Yavetskiy, R. P.; Zelenskaya, O. V.

    2013-02-01

    Density, morphology, optical transmittance and luminescence of undoped and europium-doped Lu2O3 ceramics have been studied. It has been revealed that europium ions in concentration of 5 at.% act as a solid-state sintering aids in Lu2O3 ceramics promoting its densification. Lu2O3:Eu3+ optical ceramics with relative density of 98 ± 2%, with an average grain size of 50 μm and in-line transmittance of 41% in the visible wavelength range has been produced by vacuum sintering at Т = 1850 °С. The scintillation characteristics of Lu2O3:Eu3+ ceramics under excitation with α-particles (238Рu source, E = 5.46 МeV) have been determined for the first time (S = 500 ± 50 photons/МeV, R = 26.5%).

  15. Synthesis and dielectric properties of Zn doped GdFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Sai Vandana, C.; Guravamma, J.; Hemalatha Rudramadevi, B.

    2016-09-01

    GdFeO3 and GdZn0.3Fe0.7O3 ceramics were prepared by standard Solid State Reaction method at 1200°C. The structural changes and crystallite sizes of the undoped and Zn doped ceramics were studied using the XRD data. Microstructural features and elemental composition of GdFeO3 and GdZn0.3Fe0.7O3 ceramics were determined from SEM and EDS analysis. Room temperature dielectric measurements such as dielectric constant (ɛ´), tangent loss (tan5) and AC conductivity (oac) were carried out in the frequency range (100Hz to 1MHz). Improved dielectric properties of GdZn0.3Fe0.7O3 over GdFeO3 ceramics with low values of dielectric loss render them as potential materials in the areas of microwave communication systems, information storage, spintronics, sensors, etc.

  16. Dose-Dependent Effects of CeO2 on Microstructure and Antibacterial Property of Plasma-Sprayed TiO2 Coatings for Orthopedic Application

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaobing; Liu, Gaopeng; Zheng, Hai; Cao, Huiliang; Liu, Xuanyong

    2015-02-01

    Titanium and its alloys have been used extensively for orthopedic and dental implants. Although these devices have achieved high rates of success, two major complications may be encountered: the lack of osseointegration and the biomaterial-related infection. Accordingly, cerium oxide (CeO2)-doped titanium oxide (TiO2) materials were coated on titanium by an atmospheric plasma spraying (APS) technique. The phase structures, morphologies, and surface chemical states of the obtained coatings were characterized by x-ray diffraction, scanning electron microscopy, and x-ray photoelectron spectroscopy techniques. The in vitro antibacterial and cytocompatibility of the materials were studied with Staphylococcus aureus ( S. aureus, ATCC25923) and osteoblast precursor cell line MC3T3-E1. The results indicated that the addition of CeO2 shifts slightly the diffraction peaks of TiO2 matrix to low angles but does not change its rutile phase structure. In addition, the CeO2/TiO2 composite coatings possess dose-dependent corrosion resistance and antimicrobial properties. And doping of 10 wt.% CeO2 exhibits the highest activity against S. aureus, improved corrosion resistance, and competitive cytocompatibility, which argues a promising option for balancing the osteogenetic and antibacterial properties of titanium implants.

  17. Radioluminescence properties of Sm-doped fluorochlorozirconate glasses and glass-ceramics

    NASA Astrophysics Data System (ADS)

    Okada, Go; Edgar, Andy; Kasap, Safa; Yanagida, Takayuki

    2016-02-01

    We have investigated X-ray induced radioluminescence (XL) properties of Sm-doped fluorochlorozirconate (FCZ) glasses and glass-ceramics. The FCZ glass is a modified ZBLAN glass which shows a very high optical transmission over a wide spectral range. The glass matrix includes Sm3+-doped nanocrystals of BaCl2 after heat-treatment at temperatures above 250 °C. The glass-ceramic emits red light under UV and X-ray exposure. Since conventional Si-based photodetectors, e.g., CCDs, have the highest quantum efficiency to red light in general, the Sm-doped FCZ glass-ceramic plate can be a good candidate as a scintillator material for indirect radiation detection. Moreover, a very broad emission is present in the glass-ceramic around 300-500 nm, which is attributed to a self-trapped exciton (STE) emissions. The temperature dependence of X-ray induced luminescence and photoluminescence are very similar. The XL light yield is linearly proportional to the X-ray exposure rate for rates higher than 20 mR/s. For low exposure rates, emissions by Sm2+ are more sensitive than others, leading to a nonlinear response.

  18. Optical, luminescent and laser properties of highly transparent ytterbium doped yttrium lanthanum oxide ceramics

    NASA Astrophysics Data System (ADS)

    Ivanov, M.; Kopylov, Yu.; Kravchenko, V.; Li, Jiang; Pan, Yubai; Kynast, U.; Leznina, M.; Strek, W.; Marciniak, Lukasz; Palashov, O.; Snetkov, I.; Mukhin, I.; Spassky, D.

    2015-12-01

    This paper describes the fabrication and investigation of highly transparent Yb-doped yttrium lanthanum oxide ceramics. For sintering of the ceramics we used a technology, which consists of several consecutive steps: (a) synthesis of weakly agglomerated nanopowder by laser ablation, (b) compacting of the green body with cold isostatic pressing (CIP), and (c) sintering in vacuum. After calcinations of the synthesized nanopowder at 1200 °C, a pure single-phase solid solution Yb3+:(LaxY1-x)2O3 was formed. The lanthanum ions proved to be a good aid to sinter yttria ceramics doped with Yb3+ at comparatively moderate temperatures of about 1650 °C. The ceramics have a relative density higher than 99.99% and grain sizes around 40 μm. The absorption coefficient of 3.2 mm thick Yb0.12La0.27Y1.61O3 ceramics is 0.01 cm-1 at 1150 nm. Laser oscillation at a wavelength of 1033 nm is demonstrated.

  19. Effect of samarium doping on the dielectric behavior of barium zircomium titanate ceramic

    SciTech Connect

    Badapanda, T.; Sarangi, S.; Behera, B.; Anwar, S.; Sinha, T. P.

    2014-04-24

    Samarium doped Barium Zirconium Titanate ceramic with general formula Ba{sub 1−x}Sm{sub 2x/3}Zr{sub 0.05}Ti{sub 0.95}O{sub 3} [x=0.0,0.01,0.02,0.03,0.04] has been prepared by high energy ball milling. The X-ray diffraction (XRD) patterns confirmed that these ceramics have a single phase with perovskite-type upto x≤0.03 and a small secondary phase exist at x=0.04. The temperature dependent dielectric study shows a ferroelectric phase transition and transition temperature decreases with an increase in the Samarium content.

  20. Effect of samarium doping on the dielectric behavior of barium zircomium titanate ceramic

    NASA Astrophysics Data System (ADS)

    Badapanda, T.; Sarangi, S.; Behera, B.; Anwar, S.; Sinha, T. P.

    2014-04-01

    Samarium doped Barium Zirconium Titanate ceramic with general formula Ba1-xSm2x/3Zr0.05Ti0.95O3 [x=0.0,0.01,0.02,0.03,0.04] has been prepared by high energy ball milling. The X-ray diffraction (XRD) patterns confirmed that these ceramics have a single phase with perovskite-type upto x≤0.03 and a small secondary phase exist at x=0.04. The temperature dependent dielectric study shows a ferroelectric phase transition and transition temperature decreases with an increase in the Samarium content.

  1. Structural properties of fluorozirconate-based glass ceramics doped with multivalent europium

    SciTech Connect

    PaBlick, C.; Müller, O.; Lützenkirchen-Hecht, D.; Frahm, R.; Johnson, J.A.; Schweizer, S.

    2012-10-10

    The structure/property relationships of fluorochlorozirconate glass ceramics as a function of divalent and trivalent europium (Eu) co-doping and thermal processing have been investigated; the influence of doping ratio on the formation of barium chloride (BaCl2) nanocrystals therein was elucidated. X-ray absorption near-edge structure spectroscopy shows that the post-thermal annealing changes the Eu valence of the as-poured glass slightly, but during the melting process Eu3+ is more strongly reduced to Eu2+, in particular, when doped as a chloride instead of fluoride compound. The Eu2+-to-Eu3+ doping ratio also plays a significant role in chemical equilibrium in the melt. X-ray diffraction measurements indicate that a higher Eu2+ fraction leads to a BaCl2 phase transition from hexagonal to orthorhombic structure at a lower temperature.

  2. Structural properties of fluorozirconate-based glass ceramics doped with multivalent europium

    SciTech Connect

    Passlick, C.; Mueller, O.; Luetzenkirchen-Hecht, D.; Frahm, R.; Johnson, J. A.; Schweizer, S.

    2011-12-01

    The structure/property relationships of fluorochlorozirconate glass ceramics as a function of divalent and trivalent europium (Eu) co-doping and thermal processing have been investigated; the influence of doping ratio on the formation of barium chloride (BaCl{sub 2}) nanocrystals therein was elucidated. X-ray absorption near-edge structure spectroscopy shows that the post-thermal annealing changes the Eu valence of the as-poured glass slightly, but during the melting process Eu{sup 3+} is more strongly reduced to Eu{sup 2+}, in particular, when doped as a chloride instead of fluoride compound. The Eu{sup 2+}-to-Eu{sup 3+} doping ratio also plays a significant role in chemical equilibrium in the melt. X-ray diffraction measurements indicate that a higher Eu{sup 2+} fraction leads to a BaCl{sub 2} phase transition from hexagonal to orthorhombic structure at a lower temperature.

  3. Dielectric, ferroelectric and piezoelectric properties of Nb{sup 5+} doped BCZT ceramics

    SciTech Connect

    Parjansri, Piewpan; Intatha, Uraiwan; Eitssayeam, Sukum

    2015-05-15

    Highlights: • Average grain size of BCZT ceramic decreased with the increasing Nb{sup 5+} doping. • Dielectric constant value is enhanced with Nb{sup 5+} doping. • Dielectric loss of BCZT − x Nb{sup 5+} ceramics was less than 0.03 at room temperature (1 kHz). • Piezoelectric coefficient decreased with the increasing Nb{sup 5+} doping. • The relaxation behavior is enhanced with the doping of Nb{sup 5+}. - Abstract: This work investigated the electrical properties of Nb{sup 5+} (0.0–1.0 mol%) doped with Ba{sub 0.90}Ca{sub 0.10}Zr{sub 0.10}Ti{sub 0.90}O{sub 3} while adding 1 mol% of Ba{sub 0.90}Ca{sub 0.10}Zr{sub 0.10}Ti{sub 0.90}O{sub 3} seeds. The mixed powder was ball milled for 24 h, calcined and sintered at 1200 °C for 2 h and 1450 °C for 4 h, respectively. The XRD patterns of the ceramic samples were investigated by X-ray diffraction. The electrical properties of ceramics were measured and the results indicated that all samples show a pure perovskite phase with no secondary phase. Density and average grain size values were in the range of 5.60–5.71 g/cm{sup 3} and 12.62–1.86 μm, respectively. The highest dielectric constant, ϵ{sub r} at room temperature (1 kHz) was 4636 found at 1.0 mol% Nb. The dielectric loss, tan δ was less than 0.03 for all samples at room temperature (1 kHz). Other electrical properties, P{sub r}, d{sub 33} and k{sub p} values were decreased with Nb doped relates to the decreasing grain size in BCZT ceramics. Moreover, the degrees of phase transition diffuseness and relaxation behavior were observed in the higher Nb doping.

  4. Enhanced Dielectric Properties and High-Temperature Microwave Absorption Performance of Zn-Doped Al2O3 Ceramic

    NASA Astrophysics Data System (ADS)

    Wang, Yuan; Luo, Fa; Wei, Ping; Zhou, Wancheng; Zhu, Dongmei

    2015-07-01

    To improve the dielectric and microwave absorption properties of Al2O3 ceramic, Zn-doped Al2O3 ceramic was prepared by conventional ceramic processing. X-ray diffraction analysis confirmed that Zn atoms successfully entered the Al2O3 ceramic lattice and occupied Al sites. The complex permittivity increased with increasing Zn concentration, which is mainly attributed to the increase in charged vacancy defects and densification of the Al2O3 ceramic. In addition, the temperature-dependent complex permittivity of 3% Zn-doped Al2O3 ceramic was determined in the temperature range from 298 K to 873 K. Both the real and imaginary parts of the complex permittivity increased monotonically with increasing temperature, which can be ascribed to the shortened relaxation time and increasing electrical conductivity. The increased complex permittivity leads to a great improvement in microwave absorption. In particular, when the temperature is up to 873 K, the 3% Zn-doped Al2O3 ceramic exhibited the best absorption performance with a maximum peak (-12.1 dB) and broad effective absorption bandwidth (reflection loss less than -10 dB from 9.3 GHz to 12.3 GHz). These results reveal that Zn-doped Al2O3 ceramic is a promising candidate for use as a kind of high-temperature microwave absorption material.

  5. Materials and electrical characterization of molecular beam deposited CeO2 and CeO2/HfO2 bilayers on germanium

    NASA Astrophysics Data System (ADS)

    Brunco, D. P.; Dimoulas, A.; Boukos, N.; Houssa, M.; Conard, T.; Martens, K.; Zhao, C.; Bellenger, F.; Caymax, M.; Meuris, M.; Heyns, M. M.

    2007-07-01

    Properties of CeO2 and CeO2/HfO2 bilayers grown by molecular beam deposition on in situ prepared, oxide-free Ge(100) surfaces are reported here. Deposition is achieved by a simultaneous flux of electron-beam evaporated metal (Ce or Hf) and of remote plasma generated atomic oxygen. These conditions result in an interfacial layer (IL) between the cubic CeO2 and Ge substrate. Electron energy loss spectroscopy shows that this IL is comprised of Ge and O and a small amount of Ce, and x-ray photoelectron spectroscopy suggests that the Ge is in a mix of 2+ and 3+ oxidation states. A comparison of capacitance, conductance, and leakage data shows a higher quality dielectric for 225 °C deposition than for room temperature. However, CeO2-only deposition results in an unacceptably high leakage current due to the small CeO2 band gap, which is remedied by the use of CeO2/HfO2 bilayers. Using the Nicollian-Goetzberger method, interface trap densities in the mid 1011 eV-1 cm-2 are obtained for CeO2/HfO2 gate stacks on both n- and p-Ge.

  6. Electronically conductive magnesia doped oxide ceramics for use in sodium sulfur batteries

    SciTech Connect

    Crosbie, G.M.; Tennenhouse, G.J.; Tischer, R.P.; Wroblowa, H.S.

    1984-06-26

    This invention relates to electrically conductive current collectors suitable for use at high temperatures and in the presence of corrosive environments, e.g., the sodium-sulfur battery. The current collectors comprises metal or metal alloys coated with ceramic material comprising chromium oxides doped with at least 0.05 mole percent magnesia. The corrosion resistant current collectors may be container/current collectors.

  7. Fabrication and Characterization of Dual Phase Magnesia-Zirconia Ceramics Doped with Plutonia

    SciTech Connect

    P. G. Medvedev; J. F. Jue; S. M. Frank; M.K. Meyer

    2005-05-01

    Dual phase magnesia-zirconia ceramics doped with plutonia are being studied as an inert matrix fuel (IMF) for light water reactors. The motivation of this work is to develop an IMF with a thermal conductivity superior to that of the fuels based on yttria stabilized zirconia. The concept uses the MgO phase as an efficient heat conductor to increase thermal conductivity of the composite. In this paper ceramic fabrication and characterization by scanning electron microscopy, energy and wavelength dispersive xray spectroscopy is discussed. Characterization shows that the ceramics consist of the two-phase matrix and PuO2-rich inclusions. The matrix is comprised of pure MgO phase and MgO-ZrO2-PuO2 solid solution. The PuO2-rich inclusion contained dissolved MgO and ZrO2.

  8. Spectral investigations on Dy{sup 3+}-doped transparent oxyfluoride glasses and nanocrystalline glass ceramics

    SciTech Connect

    Babu, P.; Jang, Kyoung Hyuk; Kim, Eun Sik; Shi, Liang; Seo, Hyo Jin; Rivera-Lopez, F.; Rodriguez-Mendoza, U. R.; Lavin, V.; Vijaya, R.; Jayasankar, C. K.; Rama Moorthy, L.

    2009-01-01

    Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and studied by x-ray diffraction, absorption, and visible and near-infrared emission spectra. The samples emit intense white light when populating the {sup 4}F{sub 9/2} level with a 451 nm laser light and, from the visible emission spectra, yellow to blue intensity ratios and chromaticity color coordinates have been calculated and their relative variation have been discussed based on the concentration of Dy{sup 3+} ions and the heat treatment conditions used to prepare the glass ceramics. Infrared emission has also been observed in glasses and glass ceramics after laser excitation at 800 nm, showing bands at 1.33 and 1.67 {mu}m, useful for optical amplification in fiber amplifiers.

  9. Fabrication and characterization of dual phase magnesia zirconia ceramics doped with plutonia

    NASA Astrophysics Data System (ADS)

    Medvedev, P. G.; Jue, J. F.; Frank, S. M.; Meyer, M. K.

    2006-06-01

    Dual phase magnesia-zirconia ceramics doped with plutonia are being studied as an inert matrix fuel (IMF) for light water reactors. The motivation of this work is to develop an IMF with a thermal conductivity superior to that of the fuels based on yttria stabilized zirconia. The concept uses the MgO phase as an efficient heat conductor to increase thermal conductivity of the composite. In this paper ceramic fabrication and characterization by scanning electron microscopy, energy and wavelength dispersive X-ray spectroscopy is discussed. Characterization shows that the ceramics consist of the two-phase matrix and PuO2-rich inclusions. The matrix is comprised of pure MgO phase and MgO-ZrO2-PuO2 solid solution. The PuO2-rich inclusion contained dissolved MgO and ZrO2.

  10. Huge low-frequency dielectric response of (Nb,In)-doped TiO2 ceramics

    NASA Astrophysics Data System (ADS)

    Wu, Y. Q.; Zhao, X.; Zhang, J. L.; Su, W. B.; Liu, J.

    2015-12-01

    The (Nb,In)-doped TiO2 ceramics have drawn considerable attention as a type of promising giant-permittivity dielectric materials in recent years. However, a significant controversy concerning the giant dielectric mechanism currently exists, and clarifying it is vitally important from both scientific and technological viewpoints. This letter reports the results of a systematical comparison study, where two kinds of (Nb,In)-doped TiO2 ceramics with a substantial difference in dielectric loss are used. Dielectric properties and complex impedance are investigated over a broad frequency band of 3 mHz-110 MHz. A huge low-frequency dielectric response in addition to the giant dielectric relaxation appearing above 1 MHz is observed for both kinds of (Nb,In)-doped TiO2 ceramics in dielectric dispersion. The huge dielectric response observed in the low frequency range can be ascribed to a non-ohmic electrode-contact, and the dielectric relaxation appearing above 1 MHz can be attributed to an internal barrier layer capacitance effect. An electrical equivalent circuit model suggested can well describe the observed dielectric properties and electrical behaviors.

  11. Rare-earth doped transparent ceramics for spectral filtering and quantum information processing

    SciTech Connect

    Kunkel, Nathalie Goldner, Philippe; Ferrier, Alban; Thiel, Charles W.; Cone, Rufus L.; Ramírez, Mariola O.; Bausá, Luisa E.; Ikesue, Akio

    2015-09-01

    Homogeneous linewidths below 10 kHz are reported for the first time in high-quality Eu{sup 3+} doped Y {sub 2}O{sub 3} transparent ceramics. This result is obtained on the {sup 7}F{sub 0}→{sup 5}D{sub 0} transition in Eu{sup 3+} doped Y {sub 2}O{sub 3} ceramics and corresponds to an improvement of nearly one order of magnitude compared to previously reported values in transparent ceramics. Furthermore, we observed spectral hole lifetimes of ∼15 min that are long enough to enable efficient optical pumping of the nuclear hyperfine levels. Additionally, different Eu{sup 3+} concentrations (up to 1.0%) were studied, resulting in an increase of up to a factor of three in the peak absorption coefficient. These results suggest that transparent ceramics can be useful in applications where narrow and deep spectral holes can be burned into highly absorbing lines, such as quantum information processing and spectral filtering.

  12. Microstructure evolution and electrical characterization of Lanthanum doped Barium Titanate (BaTiO3) ceramics

    NASA Astrophysics Data System (ADS)

    Billah, Masum; Ahmed, A.; Rahman, Md. Miftaur; Mahbub, Rubbayat; Gafur, M. A.; Bashar, M. Shahriar

    2016-07-01

    In the current work, we investigated the structural and dielectric properties of Lanthanum oxide (La2O3) doped Barium Titanate (BaTiO3) ceramics and established a correlation between them. Solid state sintering method was used to dope BaTiO3 with 0.3, 0.5 and 0.7 mole% La2O3 under different sintering parameters. The raw materials used were La2O3 nano powder of ~80nm grain size and 99.995% purity and BaTiO3 nano powder of 100nm grain size and 99.99% purity. Grain size distribution and morphology of fracture surface of sintered pellets were examined by Field Emission Scanning Electron Microscope and X-Ray Diffraction analysis was conducted to confirm the formation of desired crystal structure. The research result reveal that grain size and electrical properties of BaTiO3 ceramic significantly enhanced for small amount of doping (up to 0.5 mole% La2O3) and then decreased with increasing doping concentration. Desired grain growth (0.80-1.3 µm) and high densification (<90% theoretical density) were found by proper combination of temperature, sintering parameters and doping concentration. We found the resultant stable value of dielectric constant was 10000-12000 at 100-300 Hz in the temperature range of 30°-50° C for 0.5 mole% La2O3 with corresponding shift of curie temperature around 30° C. So overall this research showed that proper La3+ concentration can control the grain size, increase density, lower curie temperature and hence significantly improve the electrical properties of BaTiO3 ceramics.

  13. Structural, Dielectric, and Optical Properties of Ni-Doped Barium Cadmium Tantalate Ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Hongxue; Liu, Shaojun; Zenou, Victor Y.; Beach, Cameron; Newman, Nathan

    2006-12-01

    We report the effect of Ni-doping on the structural, dielectric and optical properties of Ba(Cd1/3Ta2/3)O3 (BCT) ceramics. Rietveld analysis of the X-ray diffraction (XRD) data indicates that the BCT structure is similar to other Ba(B'1/3B''2/3)O3 perovskites, although the Ta-O-Cd is distorted to an angle of ˜173°; very close to our earlier theoretical prediction of 172°. The XRD analysis also indicates that Ni doping significantly enhances the extent of Cd-Ta ordering in BCT. The temperature coefficient of resonant frequency decreases with Ni concentration up to 2 wt %. While the loss tangent of BCT is reduced at small levels of Ni doping (up to 0.5 wt %), it increases abruptly at higher concentrations. We found a correlation between the loss tangent of Ni-doped BCT samples and the intensity of a continuous absorption background in the optical spectra. This optical activity results from the presence of optically active point defects and is suggestive that these defects play an important role in the microwave loss in BCT ceramics.

  14. Enhanced electrical properties in multiferroic BiFeO3 ceramics co-doped by La3+ and V5+

    NASA Astrophysics Data System (ADS)

    Yu, Benfang; Li, Meiya; Wang, Jing; Pei, Ling; Guo, Dongyun; Zhao, Xingzhong

    2008-09-01

    La3+ and V5+ co-doped Bi0.85La0.15Fe1-xVxO3 (BLFVx, x = 0-0.1) ceramics were prepared by a rapid liquid sintering technique. The effects of the V5+-doping content on the structure and electrical properties of BLFVx ceramics were investigated. In the range of the V5+ content x from 0 to 0.03, BLFVx ceramics had a polycrystalline perovskite structure with tiny residual Bi2O3, while an impurity phase appeared for x > 0.03. As the x increased from 0 to 0.1, both the leakage current density and the dielectric loss (tan δ) for BLFVx ceramics decreased gradually, while the dielectric constant (ɛr) first increased and then decreased gradually in this process, reaching a maximum value of 273 for x = 0.03. Among the BLFVx ceramics, the BLFVx=0.01 ceramic showed a well-saturated hysteresis loop with large remanent polarization (Pr) of 39.4 µC cm-2 and a low coercive electric field (Ec) of ±43.1 kV cm-1 under an applied electric field of ±75 kV cm-1. In addition, these ceramics exhibited good anti-fatigue characteristics after 2 × 1010 read/write polarization cycles. These suggested that La3+ and V5+ co-doping was beneficial for enhancing the dielectric, ferroelectric and anti-fatigue properties of the BLFVx ceramics.

  15. Thermoelectric properties of SnO2-based ceramics doped with Nd, Hf or Bi

    NASA Astrophysics Data System (ADS)

    Yanagiya, S.; Nong, N. V.; Sonne, M.; Pryds, N.

    2012-06-01

    We report the thermoelectric properties of Nd-, Hf-or Bi-doped SnO2-based ceramics prepared by solid-state sintering. Polycrystalline SnO2-based samples (Sn0.97Sb0.01Zn0.01M0.01O2, M = Nd, Hf or Bi) were prepared by solid-state reactions. We confirmed that Bi-doping increased the power factor due to both the enhanced electrical conductivity and Seebeck coefficient compared to the matrix material. The maximum power factor of 4.8 × 10-4 Wm-1K-2 was attained for the Bi-doped sample at 1060 K.

  16. Redox enzyme-mimicking activities of CeO2 nanostructures: Intrinsic influence of exposed facets

    PubMed Central

    Yang, Yushi; Mao, Zhou; Huang, Wenjie; Liu, Lihua; Li, Junli; Li, Jialiang; Wu, Qingzhi

    2016-01-01

    CeO2 nanoparticles (NPs) have been well demonstrated as an antioxidant in protecting against oxidative stress-induced cellular damages and a potential therapeutic agent for various diseases thanks to their redox enzyme-mimicking activities. The Ce3+/Ce4+ ratio and oxygen vacancies on the surface have been considered as the major originations responsible for the redox enzyme-mimicking activities of CeO2 NPs. Herein, CeO2 nanostructures (nanocubes and nanorods) exposed different facets were synthesized via a facile hydrothermal method. The characterizations by X-ray photoelectron spectroscopy, Raman spectroscopy, and UV-Vis spectroscopy show that the Ce3+/Ce4+ ratio and oxygen vacancy content on the surfaces of as-synthesized CeO2 nanostructures are nearly at the same levels. Meanwhile, the enzymatic activity measurements indicate that the redox enzyme-mimicking activities of as-synthesized CeO2 nanostructures are greatly dependent on their exposed facets. CeO2 nanocubes with exposed {100} facets exhibit a higher peroxidase but lower superoxide dismutase activity than those of the CeO2 nanorods with exposed {110} facets. Our results provide new insights into the redox enzyme-mimicking activities of CeO2 nanostructures, as well as the design and synthesis of inorganic nanomaterials-based artificial enzymes. PMID:27748403

  17. Redox enzyme-mimicking activities of CeO2 nanostructures: Intrinsic influence of exposed facets

    NASA Astrophysics Data System (ADS)

    Yang, Yushi; Mao, Zhou; Huang, Wenjie; Liu, Lihua; Li, Junli; Li, Jialiang; Wu, Qingzhi

    2016-10-01

    CeO2 nanoparticles (NPs) have been well demonstrated as an antioxidant in protecting against oxidative stress-induced cellular damages and a potential therapeutic agent for various diseases thanks to their redox enzyme-mimicking activities. The Ce3+/Ce4+ ratio and oxygen vacancies on the surface have been considered as the major originations responsible for the redox enzyme-mimicking activities of CeO2 NPs. Herein, CeO2 nanostructures (nanocubes and nanorods) exposed different facets were synthesized via a facile hydrothermal method. The characterizations by X-ray photoelectron spectroscopy, Raman spectroscopy, and UV-Vis spectroscopy show that the Ce3+/Ce4+ ratio and oxygen vacancy content on the surfaces of as-synthesized CeO2 nanostructures are nearly at the same levels. Meanwhile, the enzymatic activity measurements indicate that the redox enzyme-mimicking activities of as-synthesized CeO2 nanostructures are greatly dependent on their exposed facets. CeO2 nanocubes with exposed {100} facets exhibit a higher peroxidase but lower superoxide dismutase activity than those of the CeO2 nanorods with exposed {110} facets. Our results provide new insights into the redox enzyme-mimicking activities of CeO2 nanostructures, as well as the design and synthesis of inorganic nanomaterials-based artificial enzymes.

  18. Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties.

    PubMed

    Mehdizadeh Dehkordi, Arash; Bhattacharya, Sriparna; Darroudi, Taghi; Zeng, Xiaoyu; Alshareef, Husam N; Tritt, Terry M

    2015-08-15

    We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.

  19. Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties.

    PubMed

    Mehdizadeh Dehkordi, Arash; Bhattacharya, Sriparna; Darroudi, Taghi; Zeng, Xiaoyu; Alshareef, Husam N; Tritt, Terry M

    2015-01-01

    We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3. PMID:26327483

  20. Optical thermometry based on luminescence behavior of Dy3+-doped transparent LaF3 glass ceramics

    NASA Astrophysics Data System (ADS)

    Bu, Y. Y.; Cheng, S. J.; Wang, X. F.; Yan, X. H.

    2015-11-01

    Dy3+-doped transparent LaF3 glass ceramics were fabricated, and its structures of resulting glass ceramics are studied by the X-ray diffraction and transmission electron microscopy. Optical temperature sensing of the resulting glass ceramics in the temperature range from 298 to 523 K is studied based on the down-conversion luminescence of Dy3+ ion. By using fluorescence intensity ratio method, the 4I15/2 and 4F9/2 of Dy3+ ions are verified as thermally coupled levels. A minimum S R = 1.16 × 10-4 K-1 is obtained at T = 294 K. By doping Eu3+ ion, the overall emission color of Eu3+-Dy3+ co-doped transparent glass ceramics can be tuned from white to yellow with the temperature increase through energy transfer between Eu3+ and Dy3+. Additionally, the thermal stability of the Dy3+ single-doped transparent glass ceramics becomes higher after doping Eu3+ ion.

  1. Preparation of a novel fluorescent nanocomposite: CeO2 / ANS by a simple method

    NASA Astrophysics Data System (ADS)

    Liu, X.; Lian, X.; Li, Y.; Zhang, N.

    2012-03-01

    For the first time, a novel fluorescent material, composed of CeO2/ANS nanocomposites was successfully synthesized by a simple ultrasonic method, using CeO2 nanoparticles and 8-anilino-1-naphthalenesulfonic acid (ANS) as the raw materials. The samples were characterized by scanning electron microscope (SEM), photoluminescence spectroscopy and Fourier transformation infrared spectroscopy (FTIR). The results showed that the PL intensity of the CeO2/ANS nanocomposites was higher than that of both CeO2 nanoparticles and ANS powders, and the peak wavelength was also different from the peak wavelength typical of each of the used materials, which suggests that the chemical reaction occurs between CeO2 nanoparticles and ANS molecules. In addition, the effect of the ANS concentrations on the photoluminescence of the nanocomposites was also investigated.

  2. Spectroscopic properties of transparent Er-doped oxyfluoride glass-ceramics with GdF₃.

    PubMed

    Środa, Marcin; Szlósarczyk, Krzysztof; Różański, Marek; Sitarz, Maciej; Jeleń, Piotr

    2015-01-01

    Optically active glass-ceramics (GC) with the low-phonon phases of fluorides, doped with Er(3+) was studied. Glass based on SiO₂-Al₂O₃-Na₂F₂-Na₂O-GdF₃-BaO system was obtained. Dopant were introduced to the glass in an amount of 0.01 mol Er₂O₃ per 1 mol of glass. DTA/DSC study shows multi-stage crystallization. XRD identification of obtained phases did not confirm the presence of pure GdF₃ phase. Instead of that ceramization process led to formation of NaGdF₄ and BaGdF₅. The structural changes were studied using FT-IR spectroscopic method. The study of luminescence of the samples confirmed that optical properties of the obtained GC depend on crystallizing phases during ceramization. Time resolved spectroscopy of Er-doped glass showed the 3 and 8 times increase of lifetime of emission from (4)S₃/₂ and (4)F₉/₂ states, respectively. It confirms the erbium ions have ability to locate in the low phonon gadolinium-based crystallites. The results give possibility to obtain a new material for optoelectronic application. PMID:25049170

  3. Doping of BiScO3-PbTiO3 Ceramics for Enhanced Properties

    NASA Technical Reports Server (NTRS)

    Sehirlioglu, Alp; Sayir, Ali; Dynys, Fred

    2008-01-01

    High-temperature piezoelectrics are a key technology for aeronautics and aerospace applications such as fuel modulation to increase the engine efficiency and decrease emissions. The principal challenge for the insertion of piezoelectric materials is the limitation on upper use temperature which is due to low Curie-Temperature (T(sub c) and increasing electrical conductivity. BiScO3 -PbTiO3 (BS-PT) system is a promising candidate for improving the operating temperature for piezoelectric actuators due to its high TC (>400 C). Effects of Zr and Mn doping of the BS-PT ceramics have been studied and all electrical and electromechanical properties for Sc-deficient and Ti-deficient BS- PT ceramics are reported as a function of electrical field and temperature. Donor doping with Zr and Mn (in Sc deficient compositions) increased the DC-resistivity and decreased tan at all temperatures. Resulting ceramics exhibited saturated hysteresis loops with low losses and showed no dependence on the applied field (above twice the coercive field) and measurement frequency.

  4. Spectroscopic properties of transparent Er-doped oxyfluoride glass-ceramics with GdF₃.

    PubMed

    Środa, Marcin; Szlósarczyk, Krzysztof; Różański, Marek; Sitarz, Maciej; Jeleń, Piotr

    2015-01-01

    Optically active glass-ceramics (GC) with the low-phonon phases of fluorides, doped with Er(3+) was studied. Glass based on SiO₂-Al₂O₃-Na₂F₂-Na₂O-GdF₃-BaO system was obtained. Dopant were introduced to the glass in an amount of 0.01 mol Er₂O₃ per 1 mol of glass. DTA/DSC study shows multi-stage crystallization. XRD identification of obtained phases did not confirm the presence of pure GdF₃ phase. Instead of that ceramization process led to formation of NaGdF₄ and BaGdF₅. The structural changes were studied using FT-IR spectroscopic method. The study of luminescence of the samples confirmed that optical properties of the obtained GC depend on crystallizing phases during ceramization. Time resolved spectroscopy of Er-doped glass showed the 3 and 8 times increase of lifetime of emission from (4)S₃/₂ and (4)F₉/₂ states, respectively. It confirms the erbium ions have ability to locate in the low phonon gadolinium-based crystallites. The results give possibility to obtain a new material for optoelectronic application.

  5. Luminescence properties of Eu3+-doped SiO2-LiYF4 glass-ceramic microrods

    NASA Astrophysics Data System (ADS)

    Secu, C. E.; Secu, M.

    2015-09-01

    Photoluminescence properties of the glass-ceramics microrods containing Eu3+-doped LiYF4 nanocrystals have been studied and characterized. Judd-Ofelt parameters and quantum efficiency has been computed from luminescence spectra and discussed by comparison to the glass ceramic bulk and pellet. The radiative decay rate Arad is higher in the glass ceramic rods (221 s-1) than in the glass ceramic bulk (130 s-1) but the quantum efficiency computed is very low (21%) compared to the glass-ceramic bulk (97%). There are effective non-radiative decay channels that might be related to an influence of the dimensional constraints imposed by the membrane pores during xerogel formation and subsequent glass ceramization.

  6. Rare Earth Doped High Temperature Ceramic Selective Emitters

    NASA Technical Reports Server (NTRS)

    Chubb, Donald L.; Pal, AnnaMarie; Patton, Martin O.; Jenkins, Phillip P.

    1999-01-01

    As a result of their electron structure, rare earth ions in crystals at high temperature emit radiation in several narrow bands rather than in a continuous blackbody manner. This study develops a spectral emittance model for films of rare earth containing materials. Although there are several possible rare earth doped high temperature materials, this study was confined to rare earth aluminum garnets. Good agreement between experimental and theoretical spectral emittances was found for erbium, thulium and erbium-holmium aluminum garnets. Spectral emittances of these films are sensitive to temperature differences across the film. Emitter efficiency is also a sensitive function of temperature. For thulium aluminum garnet the efficiency is 0.38 at 1700 K but only 0.19 at 1262 K.

  7. Microstructural analysis and thermoelectric properties of Sn-Al co-doped ZnO ceramics

    NASA Astrophysics Data System (ADS)

    Hoemke, Joshua; Khan, Atta Ullah; Yoshida, Hidehiro; Mori, Takao; Tochigi, Eita; Shibata, Naoya; Ikuhara, Yuichi; Sakka, Yoshio

    2016-08-01

    Sn-Al co-doped polycrystalline ZnO ceramics were prepared by sintering in air. Phase and microstructure analysis was performed by X-ray diffraction and SEM-EDS and thermoelectric properties were measured. XRD analysis showed a ZnO primary phase as well as secondary phase peaks due to the formation of a Zn2SnO4 spinel phase or SnO2(ZnO:Sn-Al)m intergrowth phase. SEM analysis revealed a dense microstructure with a small number of nanometric pores, consistent with the measured density of 5.48 g/cm3. An activated electrical conductivity characteristic of a semiconducting material was observed as well as a negative Seebeck coefficient with both values increasing in absolute value from RT to 730 °C. The power factor had a maximum value of 3.73×10-4 W m-1 K-2 at 730 °C. Thermal conductivity measurements showed a significant reduction over the measured temperature range compared to undoped ZnO. This could be attributed to grain size reduction, the formation of a nanoscale secondary phase or a reduction in crystallinity caused by Sn-Al co-doping. A maximum ZT of 0.06 was obtained at 750 °C for the Sn-Al co-doped ZnO ceramics.

  8. Influence of high magnetic field on the luminescence of Eu{sup 3+}-doped glass ceramics

    SciTech Connect

    Jiang, Wei; Chen, Weibo; Chen, Ping; Xu, Beibei; Zheng, Shuhong; Guo, Qiangbing; Liu, Xiaofeng E-mail: qjr@zju.edu.cn; Zhang, Junpei; Han, Junbo; Qiu, Jianrong E-mail: qjr@zju.edu.cn

    2014-09-28

    Rare earth (RE) doped materials have been widely exploited as the intriguing electronic configuration of RE ions offers diverse functionalities from optics to magnetism. However, the coupling of magnetism with photoluminescence (PL) in such materials has been rarely reported in spite of its fundamental significance. In the present paper, the effect of high pulsed magnetic field on the photoluminescence intensity of Eu{sup 3+}-doped nano-glass-ceramics has been investigated. In our experiment, Eu-doped oxyfluoride glass and glass ceramic were prepared by the conventional melt-quenching process and controlled heat treatment. The results demonstrate that the integrated PL intensity of Eu{sup 3+} decreases with the enhancement of magnetic field, which can be interpreted in terms of cooperation effect of Zeeman splitting and magnetic field induced change in site symmetry. Furthermore, as a result of Zeeman splitting, both blue and red shift in the emission peaks of Eu{sup 3+} can be observed, and this effect becomes more prominent with the increase of magnetic field. Possible mechanisms associated with the observed magneto-optical behaviors are suggested. The results of the present paper may open a new gate for modulation of luminescence by magnetic field and remote optical detection of magnetic field.

  9. Ultraviolet and white photon avalanche upconversion in Ho{sup 3+}-doped nanophase glass ceramics

    SciTech Connect

    Lahoz, F.; Martin, I.R.; Calvilla-Quintero, J.M.

    2005-01-31

    Ho{sup 3+}-doped fluoride nanophase glass ceramics have been synthesized from silica-based oxyfluoride glass. An intense white emission light is observed by the naked eye under near infrared excitation at 750 nm. This visible upconversion is due to three strong emission bands in the primary color components, red, green, and blue. Besides, ultraviolet signals are also recorded upon the same excitation wavelength. The excitation mechanism of both the ultraviolet and the visible emissions is a photon avalanche process with a relatively low pump power threshold at about 20 mW. The total upconverted emission intensity has been estimated to increase by about a factor of 20 in the glass ceramic compared to the precursor glass, in which an avalanche type mechanism is not generated.

  10. Enhanced multiferroic characteristics in Fe-doped BiTiO ceramics

    NASA Astrophysics Data System (ADS)

    Chen, X. Q.; Yang, F. J.; Cao, W. Q.; Wang, H.; Yang, C. P.; Wang, D. Y.; Chen, K.

    2010-07-01

    Modification of Bi 4Ti 3O 12 multiferroic ceramics prepared by a conventional solid state reaction method were investigated by substituting Ti partly with Fe. The introduction of Fe does not change the layered perovskite structure of Bi 4Ti 3O 12. Upon increasing Fe content, the remnant polarization of the samples is enhanced. The magnetism of the ceramics at room temperature develops from diamagnetism to weak ferromagnetism with increasing Fe doping. The largest variations of 15% and 6% in remnant polarization and magnetization, achieved in a Bi 4Ti 1Fe 2O 12-δ sample after poling it in a magnetic field at 1 T and a DC electric field at 30 kV/cm for 10 min, are evidence of magnetoelectric coupling between the electric dipoles and magnetic dipoles at room temperature. The present results suggest a new candidate for a room temperature multiferroic material with enhanced properties.

  11. Ni(2+) doped glass ceramic fiber fabricated by melt-in-tube method and successive heat treatment.

    PubMed

    Fang, Zaijin; Zheng, Shupei; Peng, Wencai; Zhang, Hang; Ma, Zhijun; Dong, Guoping; Zhou, Shifeng; Chen, Danping; Qiu, Jianrong

    2015-11-01

    Glass ceramic fibers containing Ni(2+) doped LiGa(5)O(8) nanocrystals were fabricated by a melt-in-tube method and successive heat treatment. Fiber precursors were prepared by drawing at high temperature where fiber core glass was melted while fiber clad glass was softened. After heat treatment, LiGa(5)O(8) nanocrystals were precipitated in the fiber core. Excited by 980 nm laser, efficient broadband near-infrared emission was observed in the glass ceramic fiber compared to that of precursor fiber. The melt-in-tube method can realize controllable crystallization and is suitable for fabrication of novel glass ceramic fibers. The Ni(2+)-doped glass ceramic fiber is promising for broadband optical amplification. PMID:26561096

  12. Ni(2+) doped glass ceramic fiber fabricated by melt-in-tube method and successive heat treatment.

    PubMed

    Fang, Zaijin; Zheng, Shupei; Peng, Wencai; Zhang, Hang; Ma, Zhijun; Dong, Guoping; Zhou, Shifeng; Chen, Danping; Qiu, Jianrong

    2015-11-01

    Glass ceramic fibers containing Ni(2+) doped LiGa(5)O(8) nanocrystals were fabricated by a melt-in-tube method and successive heat treatment. Fiber precursors were prepared by drawing at high temperature where fiber core glass was melted while fiber clad glass was softened. After heat treatment, LiGa(5)O(8) nanocrystals were precipitated in the fiber core. Excited by 980 nm laser, efficient broadband near-infrared emission was observed in the glass ceramic fiber compared to that of precursor fiber. The melt-in-tube method can realize controllable crystallization and is suitable for fabrication of novel glass ceramic fibers. The Ni(2+)-doped glass ceramic fiber is promising for broadband optical amplification.

  13. Characteristic thermoluminescence of gamma-irradiated alumina ceramics doped with some alkali metals

    NASA Astrophysics Data System (ADS)

    Henaish, B. A.; El-Agrami, A. M.; Abdel-Fattah, W. I.; Osiris, W. G.

    1994-07-01

    Thermoluminescence properties of pure Al2O3-ceramic discs doped with some oxides of alkali metals and B were investigated. Two groups of samples were studied: one with a low concentration of B and alkali oxides and the other with higher concentration. The first group shows a relatively higher stability and better reproducibility for γ-radiation and neutron-induced TL, which could be utilized in mixed radiation field dosimetry. The main disadvantage of these TL-materials is the relatively high rate of signal fading. A simple course of post irradiation heat annealing is proposed to overcome this drawback.

  14. The microstructure of erbium-ytterbium co-doped oxyfluoride glass-ceramic optical fibers

    NASA Astrophysics Data System (ADS)

    Augustyn, Elżbieta; Żelechower, Michał; Stróż, Danuta; Chrapoński, Jacek

    2012-04-01

    Oxyfluoride transparent glass-ceramics combine some features of glasses (easier shaping or lower than single crystals cost of fabrication) and some advantages of rare-earth doped single crystals (narrow absorption/emission lines and longer lifetimes of luminescent levels). Since the material seems to be promising candidate for efficient fiber amplifiers, the manufacturing as well as structural and optical examination of the oxyfluoride glass-ceramic fibers doped with rare-earth ions seems to be a serious challenge. In the first stage oxyfluoride glasses of the following compositions 48SiO2-11Al2O3-7Na2CO3-10CaO-10PbO-11PbF2-3ErF3 and 48SiO2-11Al2O3-7Na2CO3-10CaO-10PbO-10PbF2-3YbF3-1ErF3 (in molar%) were fabricated from high purity commercial chemicals (Sigma-Aldrich). The fabricated glass preforms were drawn into glass fibers using the mini-tower. Finally, the transparent Er3+ doped and Er3+/Yb3+ co-doped oxyfluoride glass-ceramic fibers were obtained by controlled heat treatment of glass fibers. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. X-ray diffraction examination (XRD) at each stage of the glass-ceramic fibers fabrication confirmed the undesirable crystallization of preforms and glass fibers has been avoided. The fibers shown their mixed amorphous-crystalline microstructure with nano-crystals of size even below 10 nm distributed in the glassy host. The crystal structure of the grown nano-crystals has been determined by XRD and confirmed by electron diffraction (SAED). Results obtained by both techniques seem to be compatible: Er3FO10Si3 (monoclinic; ICSD 92512), Pb5Al3F19 (triclinic; ICSD 91325) and Er4F2O11Si3 (triclinic; ICSD 51510) against to initially expected PbF2 crystals.

  15. Preparation of transparent neodymium-doped yttrium aluminate garnet (Nd:YAG) ceramics with the use of freeze granulation

    NASA Astrophysics Data System (ADS)

    Wajler, Anna; Węglarz, Helena; Sidorowicz, Agata; Zych, Łukasz; Nakielska, Magdalena; Jach, Katarzyna; Tomaszewski, Henryk

    2015-12-01

    This paper presents the results of the application of freeze granulation to the production of transparent neodymium-doped yttrium-aluminum garnet ceramics. Aqueous suspensions of aluminium oxide, yttrium oxide and neodymium oxide powders were prepared based on nanometric or submicronic powders which were either commercially available or prepared by precipitation. The relations between the composition of suspension, the properties of granulate and the final properties of ceramics (microstructure, optical transmission and emission spectra) were studied.

  16. High temperature dielectric relaxation anomaly of Y3+ and Mn2+ doped barium strontium titanate ceramics

    NASA Astrophysics Data System (ADS)

    Yan, Shiguang; Mao, Chaoliang; Wang, Genshui; Yao, Chunhua; Cao, Fei; Dong, Xianlin

    2014-10-01

    Relaxation like dielectric anomaly is observed in Y3+ and Mn2+ doped barium strontium titanate ceramics when the temperature is over 450 K. Apart from the conventional dielectric relaxation analysis method with Debye or modified Debye equations, which is hard to give exact temperature dependence of the relaxation process, dielectric response in the form of complex impedance, assisted with Cole-Cole impedance model corrected equivalent circuits, is adopted to solve this problem and chase the polarization mechanism in this paper. Through this method, an excellent description to temperature dependence of the dielectric relaxation anomaly and its dominated factors are achieved. Further analysis reveals that the exponential decay of the Cole distribution parameter n with temperature is confirmed to be induced by the microscopic lattice distortion due to ions doping and the interaction between the defects. At last, a clear sight to polarization mechanism containing both the intrinsic dipolar polarization and extrinsic distributed oxygen vacancies hopping response under different temperature is obtained.

  17. Ultra-broadband amplification properties of Ni2+-doped glass-ceramics amplifiers.

    PubMed

    Jiang, Chun

    2009-04-13

    The energy level, transition configuration and mathematical model of Ni(2+)-doped glass-ceramics amplifiers are presented for the first time, to the best of one's knowledge. A quasi-three-level system is employed to model the gain and noise characteristics of the doped system, and the rate and power propagation equations of the mathematical model are solved to analyze the effect of the active ion concentration, fiber length, pump power as well as thermal-quenching on the gain spectra. It is shown that our model is in agreement with experimental result, and when excited at longer wavelength, the center of gain spectra of the amplifier red shifts, the ultra-broad band room-temperature gain spectra can cover 1.25-1.65 microm range for amplification of signal in the low-loss windows of the all-wave fiber without absorption peak caused by OH group.

  18. Effect of the Addition of CeO2 to Iron Phosphate Glass for Catalytic Applications.

    PubMed

    Chung, Jae-Yeop; Kim, Jong-Hwan; Choi, Su-Yeon; Ryu, Bong-Ki

    2015-10-01

    We investigated the effect of CeO2 content on the catalytic behavior and chemical properties of the (100 - x)(80P2O5-20Fe2O3)-xCeO2 (x = 0, 4, 8, 12, 16, 20 and 24 wt%) glass system. Using thermogravimetric analysis, we confirmed that the catalytic activity increased until a CeO2 content of 16 wt%, beyond which, it decreased. The reasons for the change in the catalytic properties of the glass samples were determined using Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and density analyses. It was confirmed using the FT-IR and XPS-01s spectra that CeO2 acts as a network modifier in iron phosphate glass. When the CeO2 content is above 16 wt%, the number of non-bridging oxygen atoms decreases with increasing CeO2 content. For these reasons, the catalytic properties decrease when the CeO2 content is more than 16 wt%. From the dissolution rate measurements, it can be observed that cerium-iron phosphate has a high water resistance. Also, as we expected, it can be confirmed that the chemical durability is improved with increasing CeO2 content.

  19. CeO2 nanorods-supported transition metal catalysts for CO oxidation.

    PubMed

    Mock, Samantha A; Sharp, Shannon E; Stoner, Thomas R; Radetic, Michael J; Zell, Elizabeth T; Wang, Ruigang

    2016-03-15

    A catalytically active oxide support in combination with metal catalysts is required in order to achieve better low temperature activity and selectivity. Here, we report that CeO2 nanorods with a superior surface oxygen release/storage capability were used as an active support of transition metal (TM) catalysts (Mn, Fe, Co, Ni, Cu) for CO oxidation reaction. The as-prepared CeO2 nanorods supported 10 wt% TM catalysts were highly active for CO oxidation at low temperature, except for the Fe sample. It is found that the 10%Cu-CeO2 catalyst performed best, and it provided a lower light-off temperature with T50 (50% conversion) at 75 °C and T100 (100% conversion) of CO to CO2 at 194 °C. The atomic level surface structure of CeO2 nanorods was investigated in order to understand the improved low temperature catalytic activity. The richness of surface roughness and various defects (voids, lattice distortion, bending, steps, twinning) on CeO2 nanorods could facilitate oxygen release and storage. According to XRD and Raman analysis, copper species migrate into the bulk CeO2 nanorods to a greater degree. Since CO adsorbed over the surface of the catalyst/support is detrimental to its catalytic activity, the surface defects on the CeO2 nanorods and CeO2-TM interactions were critical to the enhanced activity.

  20. Photocatalytic and antibacterial properties of phytosynthesized CeO2 NPs using Moringa oleifera peel extract.

    PubMed

    Surendra, T V; Roopan, Selvaraj Mohana

    2016-08-01

    Biosynthetic methods are alternative approaches which are much safer than the normal techniques (physical and chemical) used for the methods for synthesis of metal nanoparticles. The benefits are sample as it is economic and environment friendly. Herein present investigation, we have reported a microwave mediated eco-friendly synthetic approach for preparing cerium oxide (CeO2) nanoparticles. Here, we used Moringa oleifera peel as the stabilizing and reducing agent towards synthesize of Ce2O NPs via microwave irradiation. The NPs were further characterized using UV-Vis, FT-IR, XRD and HR-TEM techniques. The FTIR analysis confirmed the phytochemical involvement in NPs stabilization. The crystallinity of CeO2 nanoparticles are well demonstrated through X-ray Diffraction and HR-TEM. The TEM images reveal the spherical shape of the CeO2 NPs having an average size of 45nm. Additionally, these CeO2 NPs were used successfully as a catalyst in the degradation of the dye, crystal violet. Also the antibacterial activity of the synthesized CeO2 NPs was evaluated using Staphylococcus aureus (Gram positive bacteria) and Escherichia coli (Gram negative bacteria). CeO2 NPs showed better activity on E. coli than S. aureus. We have demonstrated an eco-friendly preparation of CeO2 nanoparticles, a good photocatalyst and having better antibacterial properties.

  1. Surface passivation of CeO2 catalyst and its ultraviolet screening effect.

    PubMed

    Kang, Joo-Hee; Kim, Yun-Hee; Paek, Seung-Min; Choy, Jin-Ho

    2011-07-01

    A new strategy was attempted to fabricate CeO2 nanoparticles using the surface fluorination technique to control the particle size and suppress the catalytic activity. The fluorinated CeO2 nanoparticles are fully characterized with XRD, XANES, UV-vis spectroscopy, HR-TEM, XPS along with the evaluation of photo and thermal catalytic activities. XRD patterns were not affected by surface fluorination. That is to say, the crystalline structure of CeO2 was not deteriorated upon fluorination. The TEM analysis showed that the fluorinated CeO2 nanoparticles with the primary particle size of 7 nm could be prepared. According to the X-ray absorption near edge structure (XANES) analysis, overall XANES spectrum was not changed upon fluorination, suggesting that the local structure of fluorinated CeO2 resembled that of the starting CeO2 nanoparticles. It was also revealed that both photo and thermal catalytic activities could be almost totally suppressed at the fluorination level of ca. 6.0 wt%. It is suggested that the selective surface fluorination with fluoride could lead to fluorinated CeO2 nanoparticles, which could be applied to new fields such as the cosmetics industries. PMID:22121733

  2. Photocatalytic and antibacterial properties of phytosynthesized CeO2 NPs using Moringa oleifera peel extract.

    PubMed

    Surendra, T V; Roopan, Selvaraj Mohana

    2016-08-01

    Biosynthetic methods are alternative approaches which are much safer than the normal techniques (physical and chemical) used for the methods for synthesis of metal nanoparticles. The benefits are sample as it is economic and environment friendly. Herein present investigation, we have reported a microwave mediated eco-friendly synthetic approach for preparing cerium oxide (CeO2) nanoparticles. Here, we used Moringa oleifera peel as the stabilizing and reducing agent towards synthesize of Ce2O NPs via microwave irradiation. The NPs were further characterized using UV-Vis, FT-IR, XRD and HR-TEM techniques. The FTIR analysis confirmed the phytochemical involvement in NPs stabilization. The crystallinity of CeO2 nanoparticles are well demonstrated through X-ray Diffraction and HR-TEM. The TEM images reveal the spherical shape of the CeO2 NPs having an average size of 45nm. Additionally, these CeO2 NPs were used successfully as a catalyst in the degradation of the dye, crystal violet. Also the antibacterial activity of the synthesized CeO2 NPs was evaluated using Staphylococcus aureus (Gram positive bacteria) and Escherichia coli (Gram negative bacteria). CeO2 NPs showed better activity on E. coli than S. aureus. We have demonstrated an eco-friendly preparation of CeO2 nanoparticles, a good photocatalyst and having better antibacterial properties. PMID:27236047

  3. CeO2 nanorods-supported transition metal catalysts for CO oxidation.

    PubMed

    Mock, Samantha A; Sharp, Shannon E; Stoner, Thomas R; Radetic, Michael J; Zell, Elizabeth T; Wang, Ruigang

    2016-03-15

    A catalytically active oxide support in combination with metal catalysts is required in order to achieve better low temperature activity and selectivity. Here, we report that CeO2 nanorods with a superior surface oxygen release/storage capability were used as an active support of transition metal (TM) catalysts (Mn, Fe, Co, Ni, Cu) for CO oxidation reaction. The as-prepared CeO2 nanorods supported 10 wt% TM catalysts were highly active for CO oxidation at low temperature, except for the Fe sample. It is found that the 10%Cu-CeO2 catalyst performed best, and it provided a lower light-off temperature with T50 (50% conversion) at 75 °C and T100 (100% conversion) of CO to CO2 at 194 °C. The atomic level surface structure of CeO2 nanorods was investigated in order to understand the improved low temperature catalytic activity. The richness of surface roughness and various defects (voids, lattice distortion, bending, steps, twinning) on CeO2 nanorods could facilitate oxygen release and storage. According to XRD and Raman analysis, copper species migrate into the bulk CeO2 nanorods to a greater degree. Since CO adsorbed over the surface of the catalyst/support is detrimental to its catalytic activity, the surface defects on the CeO2 nanorods and CeO2-TM interactions were critical to the enhanced activity. PMID:26745742

  4. Nonhydrolytic Synthesis and Electronic Structure of Ligand-Capped CeO2-.delta. and CeOCl Nanocrystals

    SciTech Connect

    Depner, S.; Kort, K; Jaye, C; Fischer, D; Banerjee, S

    2009-01-01

    A novel and versatile nonhydrolytic approach is developed for the synthesis of ligand-passivated CeO2-5 and CeOCl nanocrystals soluble in nonpolar organic solvents based on the condensation of cerium alkoxides with cerium halides. The alkyl group on the metal alkoxides and the specific halide used in the synthesis are observed to considerably influence the composition and size of the obtained nanocrystals. The obtained nanocrystals are <3 nm in diameter and, owing to their surface-capping groups, yield homogeneous and clear solutions in nonpolar organic solvents with no evidence of agglomeration. The electronic structure of the obtained CeO2-5 nanocrystals has been studied using optical absorption spectroscopy and near-edge X-ray absorption fine structure spectroscopy at Ce M- and O K-edges. The latter technique provides detailed insight into the metal valence, geometric structure, and atom-projected density of states in these nanocrystals. Finally, this synthesis method has been expanded to explore the doping of La to form solid-solution CexLa1-xO2-5 nanocrystals.

  5. Er/Yb co-doped oxy-fluoride glass-ceramics core/polymer cladding optical fibers

    NASA Astrophysics Data System (ADS)

    Czerska, E.; Świderska, M.

    2014-11-01

    Erbium/ytterbium co-doped glasses can be applied as NIR laser sources (1.55 μm) or optical amplifiers in this range. About hundred meters of Er/Yb co-doped oxy-fluoride glass-ceramics fibers have been drawn from a glass preform followed by controlled annealing. Processing temperatures (drawing and annealing) were selected upon thermal analysis results (DTA/DSC plots). Glass-ceramic structure was confirmed by the XRD measurements. Obtained fibers show good optical properties. As a cladding material polymer material (acrylic resin) is considered due to its low deposition temperature and suitable value of refractive index.

  6. Preparation for CeO2/Nanographite Composite Materials and Electrochemical Degradation of Phenol by CeO2/Nanographite Cathodes.

    PubMed

    Yu, Li; Yu, Xiujuan; Sun, Tianyi; Wang, Na

    2015-07-01

    CeO2/nanographite (CeO2/nano-G) composite materials were got by chemical precipitation method with nanographite (nano-G) and cerous nitrate hexahydrate as raw materials. The microstructures of CeO2/nano-G composite materials were characterized by means of SEM, XRD, XPS and Raman. The cathodes were made by nano-G and CeO2/nano-G composite materials, respectively. The electrolysis phenol was conducted by the diaphragm cell prepared cathode and the Ti/RuO2 anode. The results indicated that the Cerium oxide is mainly in nanoscale spherical state, uniformly dispersed in the nanographite sheet surface, and there are two different oxidation states for elemental Ce, namely, Ce(III) and Ce(IV). In the diaphragm electrolysis system with the aeration conditions, the degradation rate of phenol reached 93.9% under 120 min's electrolysis. Ceria in the cathode materials might lead to an increase in the local oxygen concentration, which accelerated the two-electron reduction of O2 to hydrogen peroxide (H2O2). The removal efficiency of phenol by using the CeO2/nano-G composite cathode was better than that of the nano-G cathode.

  7. Photocatalytic activity of binary metal oxide nanocomposites of CeO2/CdO nanospheres: Investigation of optical and antimicrobial activity.

    PubMed

    Magdalane, C Maria; Kaviyarasu, K; Vijaya, J Judith; Siddhardha, Busi; Jeyaraj, B

    2016-10-01

    We report the synthesis of high quality CeO2-CdO binary metal oxide nanocomposites were synthesized by a simple chemical precipitation and hydrothermal method. Cerium nitrate and cadmium nitrate were used as precursors. Composition, structure and morphology of the nanocomposites were analyzed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). XRD pattern proves that the final product has cubic phase and the particle size diameter of the nanocomposites are 27nm, XRD results also indicated that the crystalline properties of the nanocomposite were improved without affecting the parent lattice, FESEM analysis indicates that the product is composed of spherical particles in clusters. The morphological and optical properties of CeO2-CdO nanosamples were characterized by HRTEM and DRS spectroscopy. The IR results showed high purity of products and indicated that the nanocomposites are made up of CeO2 and CdO bonds. Absorption spectra exhibited an upward shift in characteristic peaks caused by the addition of transition metal oxide, suggesting that crystallinity of both the metal oxide is improved due to specific doping level. TGA plots further confirmed the purity and stability of nanomaterials prepared. Hence the nanocomposite has cubic crystal lattice and form a homogeneous solid structure. From the result, Cd(2+) ions are embedded in the cubic crystal lattice of ceria. The growth rate increases which are ascribed to the cationic doping with a lower valence cation. Ce-Cd binary metal oxide nanocomposites showed antibacterial activity, it showed the better growth inhibition towards p.aeruginosa. Exploit of photodegradation and photocatalytic activity of large scale synthesis of CeO2-CdO binary metal oxide nanocomposites was reported.

  8. Photocatalytic activity of binary metal oxide nanocomposites of CeO2/CdO nanospheres: Investigation of optical and antimicrobial activity.

    PubMed

    Magdalane, C Maria; Kaviyarasu, K; Vijaya, J Judith; Siddhardha, Busi; Jeyaraj, B

    2016-10-01

    We report the synthesis of high quality CeO2-CdO binary metal oxide nanocomposites were synthesized by a simple chemical precipitation and hydrothermal method. Cerium nitrate and cadmium nitrate were used as precursors. Composition, structure and morphology of the nanocomposites were analyzed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). XRD pattern proves that the final product has cubic phase and the particle size diameter of the nanocomposites are 27nm, XRD results also indicated that the crystalline properties of the nanocomposite were improved without affecting the parent lattice, FESEM analysis indicates that the product is composed of spherical particles in clusters. The morphological and optical properties of CeO2-CdO nanosamples were characterized by HRTEM and DRS spectroscopy. The IR results showed high purity of products and indicated that the nanocomposites are made up of CeO2 and CdO bonds. Absorption spectra exhibited an upward shift in characteristic peaks caused by the addition of transition metal oxide, suggesting that crystallinity of both the metal oxide is improved due to specific doping level. TGA plots further confirmed the purity and stability of nanomaterials prepared. Hence the nanocomposite has cubic crystal lattice and form a homogeneous solid structure. From the result, Cd(2+) ions are embedded in the cubic crystal lattice of ceria. The growth rate increases which are ascribed to the cationic doping with a lower valence cation. Ce-Cd binary metal oxide nanocomposites showed antibacterial activity, it showed the better growth inhibition towards p.aeruginosa. Exploit of photodegradation and photocatalytic activity of large scale synthesis of CeO2-CdO binary metal oxide nanocomposites was reported. PMID:27541568

  9. Er-doped and Er, Yb co-doped oxyfluoride glasses and glass-ceramics, structural and optical properties

    NASA Astrophysics Data System (ADS)

    Lisiecki, Radosław; Augustyn, Elżbieta; Ryba-Romanowski, Witold; Żelechower, Michał

    2011-09-01

    The selected glasses and glass-ceramics pertinent to following chemical composition in mol%:48%SiO 2-11%Al 2O 3-7%Na 2O-10%CaO-10%PbO-11%PbF 2-3%ErF 3 and 48%SiO 2-11%Al 2O 3-7%Na 2O-10%CaO-10%PbO-10%PbF 2-1%ErF 3-3%YbF 3 have been manufactured from high purity components (Aldrich) at 1450 °C in normal atmosphere. Glass optical fibers were successfully drawn. Subsequently they were subject to the heat-treatment at 700 °C in various time periods. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. It has been observed that the controlled heat-treatment of oxyfluoride glass fibers results in the creation of Pb 5Al 3F 19, Er 4F 2O 11Si 3 and Er 3FO 10Si 3 crystalline phases. The identified phases were characterized by X-ray powder diffraction (XRD) and confirmed by selected area electron diffraction (SAED). The fibers consist of mixed amorphous-crystalline microstructure with nano-crystals of size even below 10 nm distributed in the glassy host. Their morphology was investigated applying high-resolution transmission electron microscopy. Optical properties and excited state relaxation dynamics of optically active ions (Er 3+, Yb 3+) in glass and glass-ceramics have been studied. Based on absorption spectra the Judd-Ofelt analysis was carried out. The main attention was directed to NIR luminescence at. 1.6 μm related to 4I 13/2 → 4I 15/2 Er 3+ and less effective emission associated with 4I 11/2 → 4I 15/2 Er 3+ and 2F 5/2 → 2F 7/2 Yb 3+ transitions. The dissimilar spectroscopic properties have been revealed for glasses and glass-ceramic samples, respectively. The reduction of emission linewidth at 1.6 and 1.0 μm combined with substantial increase of 4I 13/2 lifetimes of erbium in glass-ceramics appear to be evidences that Er 3+ ions are accommodated in crystalline phases. The structural and optical characteristics of oxyfluoride glass-ceramic

  10. Dielectric and Piezoelectric Properties of 10% KF-Doped BaTiO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Akishige, Yukikuni; Hiraki, Yuuta; Tsukada, Shinya; Xu, Jun; Morito, Shigekazu; Ohba, Takuya; Walker, Ezekiel Lee; Neogi, Arup

    2010-08-01

    10% KF-doped barium titanate powders, Ba0.9K0.1TiO2.9F0.1, were synthesized through a sol-gel process. The powders, calcined at 650 °C, consist of cubic crystalline particles of ˜70 nm in length; the particle size increases to ˜200 nm as the firing temperature increases to ca. 800 °C, above which F2 begins to evaporate. Dense ceramics were fabricated by the spark plasma sintering (SPS) method; the average grain size is ˜2 µm in lengths. The ceramics, well annealed at 1,000 °C in an O2 gas flow, have good dielectric and piezoelectric properties; the piezoelectric d33 value is 230 pC/N at room temperature. At the ferroelectric Curie temperature TC = 47 °C, the dielectric constant and loss tan δ are 10,000 and <5% at 10 kHz, respectively. The Curie-Weiss relation holds in the fully disordered cubic and ordered rhombohedral phases, showing the second order 1:2 relation. Below 10 kHz, large dielectric dispersion caused by a domain-wall motion appears at the temperature range of -50 to 107 °C. Some discussions are made for these dielectric properties of the ceramics.

  11. Differentiation of human mesenchymal stem cells on niobium-doped fluorapatite glass-ceramics

    PubMed Central

    Kushwaha, Meenakshi; Pan, Xueliang; Holloway, Julie A.; Denry, Isabelle L.

    2011-01-01

    Objectives Our goal was to characterize the response of human mesenchymal stem cells (hMSCs) to a niobium-doped fluorapatite-based glass-ceramic (FAp). Methods The glass was prepared by twice melting at 1525°C for 3h, and cast into cylindrical ingots later sectioned into discs and heat-treated to promote crystallization of fluorapatite submicrometer crystals. Tissue culture polystyrene (TCP) was used as control. The surface of the FAp discs was either left as-heat treated, ground or etched. Initial cell attachment was assessed at 3h. Proliferation and alkaline phosphatase (ALP) expression data was collected at days 1, 4, and 8. Cell morphology was examined using SEM, at days 2 and 4. Mineralization was evaluated by Alizarin Red staining and SEM. Results Initial cell attachment on as heat-treated, etched, or ground surfaces was similar to that of the positive control group (p>0.05). The percentage of area covered by living cells increased significantly on as heat-treated, etched, or ground surfaces between days 1 and 8 (p<0.05). There was no significant difference amongst groups in cell coverage at day 8, compared to TCP control. SEM revealed well spread polygonal cells with numerous filopodia, either attached to the ceramic surface or connected to neighboring cells. ALP expression at day 8 was significantly higher in osteogenic media compared to growth media on both FAp and control. FAp discs stained positively with alizarin red and calcium-rich mineralized granules associated with fibrils were observed by SEM at day 35. Significance hMSCs displayed excellent attachment, proliferation, and differentiation on niobium-doped FAp glass-ceramic. PMID:22078764

  12. Fruit juice extract mediated synthesis of CeO2 nanoparticles for antibacterial and photocatalytic activities

    NASA Astrophysics Data System (ADS)

    Reddy Yadav, L. S.; Manjunath, K.; Archana, B.; Madhu, C.; Raja Naika, H.; Nagabhushana, H.; Kavitha, C.; Nagaraju, G.

    2016-05-01

    Ceria ( CeO2 is a technologically important rare-earth material because of its unique properties and various engineering/biological applications. In the present work, cerium oxide nanoparticles have been prepared by a simple solution combustion method using watermelon juice as a novel combustible fuel. The structure and morphology of the synthesized CeO2 nanoparticles were analyzed using various analytical tools such as PXRD, FTIR, Raman, UV-Visible and SEM. PXRD pattern confirms that the prepared material is composed of cubic-phase cerium oxide nanoparticles. Photocatalytic degradation of Methylene blue dye using CeO2 nanoparticles shows 98% of degradation in UV irradiations. Furthermore the antibacterial properties of CeO2 nanoparticles were investigated by their bacterial activity against two bacterial strains using the agar well diffusion method.

  13. Structural phase transitions in Ti-doped Bi1-xNdxFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Kalantari, Kambiz; Sterianou, Iasmi; Sinclair, Derek C.; Bingham, Paul A.; Pokorný, Jan; Reaney, Ian M.

    2012-03-01

    Recently, it was demonstrated that donor doping with Ti on the B-site significantly reduces the conductivity in Bi0.85Nd0.15FeO3 ceramics [Kalantari et al., Adv. Funct. Mater. 21, 3737 (2011)]. In this contribution, the phase transitions as a function of Nd concentration are investigated in 3% Ti doped Bi1-xNdxFeO3 ceramics. Paraelectric (PE) to ferroelectric (FE) transitions were observed for compositions with x ≤ 0.125 which manifested themselves as peaks in permittivity. In contrast, PE to antiferroelectric (AFE) transitions for 0.15 ≤ x ≤ 0.20 gave rise to a step-like change in the permittivity with x = 0.25 exhibiting no sharp anomalies and remaining PE until room temperature. The large volume change at the PE to FE/AFE transitions, reported by Levin and co-workers [Phys. Rev. B 81, 020103 (2011)] and observed here by dilatometry, coupled with their first-order character constrain the transitions to occur uniformly throughout the material in an avalanche-like manner. Hence, the anomalies in DSC, permittivity and thermal expansion occur over a commensurately narrow temperature interval. However, despite the large volume change and eye-catching anomalies in DSC, the latent heats for the transitions in Ti-doped Bi1-xNdxFeO3 are similar to Pb(Zr,Ti)O3 (1-3 kJ/mol) with each an order of magnitude greater than BaTiO3 (˜0.2 kJ/mol). A broad frequency dependent dielectric anomaly of unknown origin in the temperature range 250-450 °C was also observed in all samples.

  14. Luminescence properties of barium--gadolinium-titanate ceramics doped with rare-earth ions (Eu3+ and Tb3+).

    PubMed

    Hemasundara Raju, S; Muni Sudhakar, B; Sudhakar Reddy, B; Dhoble, S J; Thyagarajan, K; Nageswara Raju, C

    2014-11-01

    Barium-gadolinium-titanate (BaGd2 Ti4 O12) powder ceramics doped with rare-earth ions (Eu(3+) and Tb(3+)) were synthesized by a solid-state reaction method. From the X-ray diffraction spectrum, it was observed that Eu(3+) and Tb(3+):BaGd2 Ti4 O12 powder ceramics are crystallized in the form of an orthorhombic structure. Scanning electron microscopy image shows that the particles are agglomerated and the particle size is about 200 nm. Eu(3+) - and Tb(3+) -doped BaGd2 Ti4 O12 powder ceramics were examined by energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, photoluminescence and thermoluminescence (TL) spectra. Emission spectra of Eu(3+)-doped BaGd2 Ti4 O12 powder ceramics showed bright red emission at 613 nm ((5)D0 →(7)F2) with an excitation wavelength λ(exci)  = 408 nm ((7)F0 → (5)D3) and Tb(3+):BaGd2 Ti4 O12 ceramic powder has shown green emission at 534 nm ((5)D4 → (7)F5) with an excitation wavelength λ(exci)  = 331 nm (((7)F6 → (5)D1). TL spectra show that Eu(3+) and Tb(3+) ions affect TL sensitivity.

  15. Leucas aspera mediated multifunctional CeO2 nanoparticles: Structural, photoluminescent, photocatalytic and antibacterial properties.

    PubMed

    Malleshappa, J; Nagabhushana, H; Sharma, S C; Vidya, Y S; Anantharaju, K S; Prashantha, S C; Daruka Prasad, B; Raja Naika, H; Lingaraju, K; Surendra, B S

    2015-01-01

    Spherical shaped cerium dioxide (CeO2) nanoparticles (NPs) were synthesized via bio mediated route using Leucas aspera (LA) leaf extract. The NPs were characterized by PXRD, SEM, UV-Visible techniques. Photoluminescence (PL), photocatalysis and antibacterial properties of NPs were studied. PXRD patterns and Rietveld analysis confirm cubic fluorite structure with space group Fm-3m. SEM results evident that morphology of the NPs was greatly influenced by the concentration of LA leaf extract in the reaction mixture. The band gap energy of the NPs was found to be in the range of 2.98-3.4 eV. The photocatalytic activity of NPs was evaluated by decolorization of Rhodamine-B (RhB) under UVA and Sun light irradiation. CeO2 NPs show intense blue emission with CIE coordinates (0.14, 0.22) and average color coordinated temperature value ∼148,953 K. Therefore the present NPs quite useful for cool LEDs. The superior photocatalytic activity was observed for CeO2 NPs with 20 ml LA under both UVA and Sunlight irradiation. The enhanced photocatalytic activity and photoluminescent properties were attributed to defect induced band gap engineered CeO2 NPs. Further, CeO2 with 20 ml LA exhibit significant antibacterial activity against Escherichia coli (EC) and Staphylococcus aureus (SA). These findings show great promise of CeO2 NPs as multifunctional material for various applications.

  16. Hexagonal CeO2 nanostructures: an efficient electrode material for supercapacitors.

    PubMed

    Maheswari, Nallappan; Muralidharan, Gopalan

    2016-09-28

    Cerium oxide (CeO2) has emerged as a new and promising pseudocapacitive material due to its prominent valance states and extensive applications in various fields. In the present study, hexagonal CeO2 nanostructures have been prepared via the hydrothermal method employing cationic surfactant cetyl trimethyl ammonium bromide (CTAB). CTAB ensures a slow rate of hydrolysis to form small sized CeO2 nanostructures. The role of calcination temperature on the morphological, structural, electrochemical properties and cyclic stability has been assessed for supercapacitor applications. The mesoscopic hexagonal architecture endows the CeO2 with not only a higher specific capacity, but also with an excellent rate capability and cyclability. When the charge/discharge current density is increased from 2 to 10 A g(-1) the reversible charge capacity decreased from 927 F g(-1) to 475 F g(-1) while 100% capacity retention at a high current density of 20 A g(-1) even after 1500 cycles could be achieved. Furthermore, the asymmetric supercapacitor based on CeO2 exhibited a significantly higher energy density of 45.6 W h kg(-1) at a power density of 187.5 W kg(-1) with good cyclic stability. The electrochemical richness of the CeO2 nanostructure makes it a suitable electrode material for supercapacitor applications.

  17. Toxicity of CeO2 nanoparticles - the effect of nanoparticle properties.

    PubMed

    Leung, Yu Hang; Yung, Mana M N; Ng, Alan M C; Ma, Angel P Y; Wong, Stella W Y; Chan, Charis M N; Ng, Yip Hang; Djurišić, Aleksandra B; Guo, Muyao; Wong, Mabel Ting; Leung, Frederick C C; Chan, Wai Kin; Leung, Kenneth M Y; Lee, Hung Kay

    2015-04-01

    Conflicting reports on the toxicity of CeO2 nanomaterials have been published in recent years, with some studies finding CeO2 nanoparticles to be toxic, while others found it to have protective effects against oxidative stress. To investigate the possible reasons for this, we have performed a comprehensive study on the physical and chemical properties of nanosized CeO2 from three different suppliers as well as CeO2 synthesized by us, and tested their toxicity. For toxicity tests, we have studied the effects of CeO2 nanoparticles on a Gram-negative bacterium Escherichia coli in the dark, under ambient and UV illuminations. We have also performed toxicity tests on the marine diatom Skeletonema costatum under ambient and UV illuminations. We found that the CeO2 nanoparticle samples exhibited significantly different toxicity, which could likely be attributed to the differences in interactions with cells, and possibly to differences in nanoparticle compositions. Our results also suggest that toxicity tests on bacteria may not be suitable for predicting the ecotoxicity of nanomaterials. The relationship between the toxicity and physicochemical properties of the nanoparticles is explicitly discussed in the light of the current results. PMID:25768267

  18. Toxicity of CeO2 nanoparticles - the effect of nanoparticle properties.

    PubMed

    Leung, Yu Hang; Yung, Mana M N; Ng, Alan M C; Ma, Angel P Y; Wong, Stella W Y; Chan, Charis M N; Ng, Yip Hang; Djurišić, Aleksandra B; Guo, Muyao; Wong, Mabel Ting; Leung, Frederick C C; Chan, Wai Kin; Leung, Kenneth M Y; Lee, Hung Kay

    2015-04-01

    Conflicting reports on the toxicity of CeO2 nanomaterials have been published in recent years, with some studies finding CeO2 nanoparticles to be toxic, while others found it to have protective effects against oxidative stress. To investigate the possible reasons for this, we have performed a comprehensive study on the physical and chemical properties of nanosized CeO2 from three different suppliers as well as CeO2 synthesized by us, and tested their toxicity. For toxicity tests, we have studied the effects of CeO2 nanoparticles on a Gram-negative bacterium Escherichia coli in the dark, under ambient and UV illuminations. We have also performed toxicity tests on the marine diatom Skeletonema costatum under ambient and UV illuminations. We found that the CeO2 nanoparticle samples exhibited significantly different toxicity, which could likely be attributed to the differences in interactions with cells, and possibly to differences in nanoparticle compositions. Our results also suggest that toxicity tests on bacteria may not be suitable for predicting the ecotoxicity of nanomaterials. The relationship between the toxicity and physicochemical properties of the nanoparticles is explicitly discussed in the light of the current results.

  19. Reinforced magnetic properties of Ni-doped BiFeO3 ceramic

    NASA Astrophysics Data System (ADS)

    Hwang, J. S.; Yoo, Y. J.; Lee, Y. P.; Kang, J.-H.; Lee, K. H.; Lee, B. W.; Park, S. Y.

    2016-08-01

    Multiferroic materials attract considerable interest because of the wide range of potential applications such as spintronic devices, data storage devices and sensors. As a strong candidate for the applications among the limited list of single-phase multiferroic materials, BiFeO3 (BFO) is a quite attractive material due to its multiferroic properties at room temperature (RT). However, BFO is widely known to have large leakage current and small spontaneous polarization due to the existence of crystalline defects such as oxygen vacancies. Furthermore, the magnetic moment of pure BFO is very weak owing to its antiferromagnetic nature. In this paper, the effects of Ni2+ substitution on the magnetic properties of bulk BFO were investigated. BFO, and BiFe0.99Ni0.01O3, BiFe0.98Ni0.02O3 and BiFe0.97Ni0.03O3 (BFNO: Ni-doped BFO) ceramics were prepared by solid-state reaction and rapid sintering, and analyzed by structural and magnetic-property measurements. The leakage current density was measured at RT by using a standard ferroelectric tester. All the Ni-doped BFO samples exhibited the similar rhombohedral perovskite structure ( R3c) to that of BFO. The magnetic properties of Ni-doped BFO were much enhanced with respect to BFO prepared at the same conditions, because the enhanced ferromagnetic interaction is caused by the Fe/Ni coupling.

  20. Improved Thermoelectric Performances of SrTiO3 Ceramic Doped with Nb by Surface Modification of Nanosized Titania.

    PubMed

    Li, Enzhu; Wang, Ning; He, Hongcai; Chen, Haijun

    2016-12-01

    Nb-doped SrTiO3 ceramics doped with the surface modification of nanosized titania was prepared via liquid phase deposition approach and subsequent sintered in an Ar atmosphere. The surface modification of nanosized titania significantly improved the ratio of the electrical conductivity to thermal conductivity of SrTiO3 ceramic doped with Nb, and has little impact on the Seebeck coefficient, thus obviously improving the dimensionless thermoelectric figure of merit (ZT value). The surface modification of nanosized titania is a much better method to lower the thermal conductivity and to enhance the electrical conductivity than the mechanical mixing process of nanosized titania. The highest ZT value of 0.33 at 900 K was obtained. The reason for the improved thermoelectric performances by the surface modification of nano-sized titania was preliminary investigated.

  1. Visible photoluminescence in polycrystalline terbium doped aluminum nitride (Tb:AlN) ceramics with high thermal conductivity

    SciTech Connect

    Wieg, A. T.; Kodera, Y.; Wang, Z.; Garay, J. E.; Imai, T.; Dames, C.

    2012-09-10

    Thermal management continues to be one of the major challenges in the development of high powered light sources such as solid state lasers. In particular, the relatively low thermal conductivity of standard photoluminescent (PL) materials limits the overall power output and/or duty cycle. We present a method based on current activated pressure assisted densification for the fabrication of high thermal conductivity PL materials: rare earth doped polycrystalline bulk aluminum nitride. Specifically, the ceramics are translucent and are doped with Tb{sup 3+}, allowing for emission in the visible. Remarkably, the ceramics have a room temperature thermal conductivity of 94 W/(m K) which is almost seven times higher than that of the state of the art host material, Nd-doped yttrium aluminum garnet. These light emitting properties coupled with very high thermal conductivity should enable the development of a wide variety of more powerful light sources.

  2. Influence of CeO2 nanoparticles on growth and physiology of sorghum

    NASA Astrophysics Data System (ADS)

    Mu, Linlin; Liang, Wei-zhen; Kinsey, Erin; Rauh, Bradley; Kresovich, Stephen; Darnault, Christophe

    2016-04-01

    Cerium oxide nanoparticles (CeO2 NPs) are commonly used as polishing agents for industry and fuel additives to decrease the particulate matter emissions. CeO2 NPs may be encountered in the soil and water environment through their life cycle or accidental releases, and have potential phytotoxicity effects. Therefore, it is critical to assess the potential effects of CeO2 NPs in soil on plant growth and physiology. The objective of this research is to determine the physiological responses of three sorghums (Grassl, BtX623 and Rio) to the effect of CeO2 nanoparticles in potting soil environment. Sorghums were germinated and grown in potting soil in the greenhouse for three weeks cultivation with treatments of 0, 100, 500, 1000 mg CeO2 NPs per kg soil. Plant parameters, such as length, weight, and biomass of root and leaves were measured in each treatment with 12 replications. After three weeks germination, the sorghum plants were dig out and the roots were examined and scanned by the Silverfast SE Plus scanner to compare and analyze their dimensions and shapes. To further study the growth and physiological changes in plants due to the presence of CeO2 NPs in soil, one selected type of sorghum (Grassl) was grown under the four different CeO2 NPs concentration treatments for six months until plant maturity, and was also cut and harvested three times to study CeO2 NPs effect on plant re-growth. At the end of each growing period, above ground vegetative tissues were air-dried, grounded to 2mm particle size and compositional traits were estimated by using near-infrared spectroscopy. The influence of nanoparticles was observed on some of the plant traits. Preliminary results showed the influence of CeO2 NPs on the roots growth, as Grassl and Btx623 in 100 mgkg-1 treatment grew significantly faster than other concentrations; however no significant difference between control and 100 mgkg-1 treatment in Rio. CeO2 NPs concentration of 100 mgkg-1 had no impact on sorghum growth, compared to the control treatment. Results of the six months growth and repetitive cutting experiments indicated that the different treatments, including the presence and/or concentrations of the nanoparticles, impacted some of the compositional traits of sorghum.

  3. Influence of CeO2 nanoparticles on growth and physiology of sorghum

    NASA Astrophysics Data System (ADS)

    Mu, Linlin; Liang, Wei-zhen; Kinsey, Erin; Rauh, Bradley; Kresovich, Stephen; Darnault, Christophe

    2016-04-01

    Cerium oxide nanoparticles (CeO2 NPs) are commonly used as polishing agents for industry and fuel additives to decrease the particulate matter emissions. CeO2 NPs may be encountered in the soil and water environment through their life cycle or accidental releases, and have potential phytotoxicity effects. Therefore, it is critical to assess the potential effects of CeO2 NPs in soil on plant growth and physiology. The objective of this research is to determine the physiological responses of three sorghums (Grassl, BtX623 and Rio) to the effect of CeO2 nanoparticles in potting soil environment. Sorghums were germinated and grown in potting soil in the greenhouse for three weeks cultivation with treatments of 0, 100, 500, 1000 mg CeO2 NPs per kg soil. Plant parameters, such as length, weight, and biomass of root and leaves were measured in each treatment with 12 replications. After three weeks germination, the sorghum plants were dig out and the roots were examined and scanned by the Silverfast SE Plus scanner to compare and analyze their dimensions and shapes. To further study the growth and physiological changes in plants due to the presence of CeO2 NPs in soil, one selected type of sorghum (Grassl) was grown under the four different CeO2 NPs concentration treatments for six months until plant maturity, and was also cut and harvested three times to study CeO2 NPs effect on plant re-growth. At the end of each growing period, above ground vegetative tissues were air-dried, grounded to 2mm particle size and compositional traits were estimated by using near-infrared spectroscopy. The influence of nanoparticles was observed on some of the plant traits. Preliminary results showed the influence of CeO2 NPs on the roots growth, as Grassl and Btx623 in 100 mgkg‑1 treatment grew significantly faster than other concentrations; however no significant difference between control and 100 mgkg‑1 treatment in Rio. CeO2 NPs concentration of 100 mgkg‑1 had no impact on sorghum growth, compared to the control treatment. Results of the six months growth and repetitive cutting experiments indicated that the different treatments, including the presence and/or concentrations of the nanoparticles, impacted some of the compositional traits of sorghum.

  4. Room temperature magnetic and dielectric properties of cobalt doped CaCu3Ti4O12 ceramics

    NASA Astrophysics Data System (ADS)

    Mu, Chunhong; Song, Yuanqiang; Wang, Haibin; Wang, Xiaoning

    2015-05-01

    CaCu3Ti4-xCoxO12 (x = 0, 0.2, 0.4) ceramics were prepared by a conventional solid state reaction, and the effects of cobalt doping on the room temperature magnetic and dielectric properties were investigated. Both X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the presence of Cu and Co rich phase at grain boundaries of Co-doped ceramics. Scanning electron microscopy micrographs of Co-doped samples showed a striking change from regular polyhedral particle type in pure CaCu3Ti4O12 (CCTO) to sheet-like grains with certain growth orientation. Undoped CaCu3Ti4O12 is well known for its colossal dielectric constant in a broad temperature and frequency range. The dielectric constant value was slightly changed by 5 at. % and 10 at. % Co doping, whereas the second relaxation process was clearly separated in low frequency region at room temperature. A multirelaxation mechanism was proposed to be the origin of the colossal dielectric constant. In addition, the permeability spectra measurements indicated Co-doped CCTO with good magnetic properties, showing the initial permeability (μ') as high as 5.5 and low magnetic loss (μ″ < 0.2) below 3 MHz. And the interesting ferromagnetic superexchange coupling in Co-doped CaCu3Ti4O12 was discussed.

  5. Mixed electron emission from doped Pb(Zr,Ti)O{sub 3} ceramics: Microstructural aspects

    SciTech Connect

    Zhang, W.; Huebner, W.

    1998-06-01

    A mixed type electron emission, i.e., simultaneous ferroelectric and plasma emission, was observed with a negative driving pulse applied to doped Pb(Zr,Ti)O{sub 3} ceramics in the absence of any external potential on the electron collector. During these emission studies, significant microstructural changes on the emission surface were observed, and corresponded to the different emission modes. Erosion craters at the edge of the electrode and small particles near these craters reflected the formation of a dense plasma there. Comparatively, cavities, i.e., grain pullouts, accumulated on the bare ferroelectric surface, the frequency of which depended upon its distance from the grid. This phenomenon is proposed to be a result of fringing fields and the associated strain energy due to 90{degree} domain switching, which could be seen as an evidence that ferroelectric emission occurred in these areas. {copyright} {ital 1998 American Institute of Physics.}

  6. Structural and dielectric properties of CuO-doped SrTiO{sub 3} ceramics

    SciTech Connect

    Naidu, K. Chandra Babu Sarmash, T. Sofi; Maddaiah, M.; Reddy, V. Narasimha; Subbarao, T.

    2015-06-24

    Copper-doped SrTiO{sub 3} (ST) ceramic powders were processed by solid-state route diffusion (SRD) bulk preparation technique. We reported the effect of Cu{sup +2} ions on the dielectric response of ST and it established the substantial increase in dielectric constant (ε{sub r}) than undoped ST from 303K-673K and low loss (tanδ) for good dielectric applications. In respect of the electrical properties ac- activation energies were computed of range 0.089-0.319eV using lnσ Vs 1/T plots. The microstructure was examined with grain sizes 6-9µm of uniform distribution by field emission scanning electron microscope (FESEM). Some additional phases SrCu{sub 3}Ti{sub 4}O{sub 12} and TiO{sub 2} rutiles were detected by X-ray diffraction technique.

  7. Investigation on the structural and photoluminescent properties of chromium-doped ceramics cordierite

    NASA Astrophysics Data System (ADS)

    da Silva, M. A. F. M.; Pedro, S. S.; López, A.; Sosman, L. P.

    2016-10-01

    This work presents the investigation about the structural and optical properties of a doped-chromium system containing cordierite (Mg2Al4Si5O18) as main phase. The sample composition and the structural data were obtained from X-ray diffraction (XRD) measurements and the results were analyzed by Rietveld method. Photoluminescence (PL) spectra under several excitation wavelengths and photoluminescence excitation (PLE) measurements were performed. The obtained results from PL and PLE experiments are evidences that Cr3+ occupies octahedral sites in this ceramic system. By correlating the optical results, the crystal field parameter (Dq) and Racah interelectronic repulsion parameters (B and C) were calculated and discussed according to the Tanabe-Sugano (TS) theory for d3 transition metals in octahedral sites.

  8. Low-threshold and broadly tunable lasers of Yb3+-doped yttrium lanthanum oxide ceramic

    NASA Astrophysics Data System (ADS)

    Hao, Qiang; Li, Wenxue; Zeng, Heping; Yang, Qiuhong; Dou, Chuanguo; Zhou, Hongxu; Lu, Wei

    2008-05-01

    We experimentally demonstrated diode-pumped continuous wave and tunable laser operation of Yb3+-doped yttrium lanthanum oxide transparent ceramic [Yb:(Y1-xLax)2O3,x=0.1], which was fabricated with nanopowders and sintered in H2 atmosphere. As low as 400mW pumping threshold and a slope efficiency of 52% were realized at 1080nm under a high-brightness 976nm diode pump with a fiber core of 50μm and a numerical aperture of 0.22. A maximum output power of 2.1W was obtained when the non-lasing absorbed pump power was 19.5W at 976nm with diode laser of 400μm fiber core. A smooth tunable curve from 1018to1086nm was achieved at 940nm diode pump. Broadband lasing spectra up to 30nm were observed in the tunable laser experiment.

  9. High quality Y3Al5O12 doped transparent ceramics for laser applications, role of sintering additives

    NASA Astrophysics Data System (ADS)

    Kaminskii, A. A.; Balashov, V. V.; Cheshev, E. A.; Kopylov, Yu L.; Koromyslov, A. L.; Krokhin, O. N.; Kravchenko, V. B.; Lopukhin, K. V.; Shemet, V. V.; Tupitsyn, I. M.

    2016-08-01

    SiO2, ZrO2, B2O3 and MgO oxides and their combinations were used as sintering aids for preparation of yttrium aluminum garnet (YAG) ceramics doped by Nd2O3, Er2O3, Ho2O3, Tm2O3 and Yb2O3. The influence of these additives on optimal sintering temperature, grain growth, volume of residual pores and optical quality of the ceramics were investigated. The best combination of the sintering additives was found and high quality samples of YAG:Nd (1 at.%) ceramics were obtained. The original method of laser optical quality characterization of ceramics was developed and tested. The main laser parameters of YAG:Nd (1 at.%) ceramics samples are measured and compared with the best well known laser ceramics. The samples of YAG:RE (RE- Er2O3, Ho2O3, Tm2O3 and Yb2O3) ceramics are obtained, and their optical transmittance spectra are measured. Composite structures of YAG:Yb (5 at.%) - YAG were obtained by the simplest method of successive joint compaction of different composition layers.

  10. Blocking effect of crystal–glass interface in lanthanum doped barium strontium titanate glass–ceramics

    SciTech Connect

    Wang, Xiangrong; Zhang, Yong; Baturin, Ivan; Liang, Tongxiang

    2013-10-15

    Graphical abstract: The blocking effect of the crystal–glass interface on the carrier transport behavior in the lanthanum doped barium strontium titanate glass–ceramics: preparation and characterization. - Highlights: • La{sub 2}O{sub 3} addition promotes the crystallization of the major crystalline phase. • The Z″ and M″ peaks exist a significant mismatch for 0.5 mol% La{sub 2}O{sub 3} addition. • The Z″ and M″ peaks separate obviously for 1.0 mol% La{sub 2}O{sub 3} addition. • Crystallite impedance decreases while crystal–glass interface impedance increases. • La{sub 2}O{sub 3} addition increases blocking factor of the crystal–glass interface. - Abstract: The microstructures and dielectric properties in La{sub 2}O{sub 3}-doped barium strontium titanate glass–ceramics have been investigated by scanning electron microscopy (SEM) and impedance spectroscopy. SEM analysis indicated that La{sub 2}O{sub 3} additive decreases the average crystallite size. Impedance spectroscopy revealed that the positions of Z″ and M″ peaks are close for undoped samples. When La{sub 2}O{sub 3} concentration is 0.5 mol%, the Z″ and M″ peaks show a significant mismatch. Furthermore, these peaks separate obviously for 1.0 mol% La{sub 2}O{sub 3} addition. With increasing La{sub 2}O{sub 3} concentration, the contribution of the crystallite impedance becomes smaller, while the contribution of the crystal–glass interface impedance becomes larger. More interestingly, it was found that La{sub 2}O{sub 3} additive increases blocking factor of the crystal–glass interface in the temperature range of 250–450 °C. This may be attributed to a decrease of activation energy of the crystallite and an increase of the crystal–glass interface area.

  11. Fabrication of Dual Phase Magnesia-Zirconia Ceramics Doped with Plutonia and Erbia

    SciTech Connect

    Paul A. Lessing; Timothy A. Hyde

    2006-06-01

    Dual phase magnesia-zirconia ceramics doped with plutonia and erbia are being evaluated as an inert matrix fuel (IMF) for light water reactors (LWR). The motivation for this work is to develop an IMF with a thermal conductivity superior to that of the fuels based on single-phase yttria stabilized zirconia. The innovative fuel developed at INL is comprised of two major phases: pure MgO and quaternary solid solution consisting of MgO, ZrO{sub 2}, Er{sub 2}O{sub 3} and PuO{sub 2}. Pure MgO phase acts as an efficient heat conductor. It has been shown [1] that dual phase MgO-ZrO{sub 2} ceramics have the thermal conductivity superior to that of UO{sub 2} and have notable chemical resistance to water at the temperature of 573 K and pressure 8.6 MPa, which makes them attractive for use as an IMF matrix in LWRs.

  12. Fabrication of dual phase magnesia-zirconia ceramics doped with plutonia and erbia

    SciTech Connect

    P. G. Medvedev; J. F. Jue; S. M. Frank

    2006-06-01

    Dual phase magnesia-zirconia ceramics doped with plutonia and erbia are being evaluated as an inert matrix fuel (IMF) for light water reactors (LWR). The motivation for this work is to develop an IMF with a thermal conductivity superior to that of the fuels based on single-phase yttria stabilized zirconia. The innovative fuel developed at INL is comprised of two major phases: pure MgO and quaternary solid solution consisting of MgO, ZrO{sub 2}, Er{sub 2}O{sub 3} and PuO{sub 2}. Pure MgO phase acts as an efficient heat conductor. It has been shown [1] that dual phase MgO-ZrO{sub 2} ceramics have the thermal conductivity superior to that of UO{sub 2} and have notable chemical resistance to water at the temperature of 573 K and pressure 8.6 MPa, which makes them attractive for use as an IMF matrix in LWRs.

  13. Effect of crystallization heat treatment on the microstructure of niobium-doped fluorapatite glass-ceramics.

    PubMed

    Denry, I; Holloway, J A; Gupta, P K

    2012-07-01

    Our goal was to study the effect of heat treatment temperature and heating rate on the microstructure and crystalline phases and assess the domain of existence of submicrometer fluorapatite crystals in niobium-doped fluorapatite glass-ceramics for biomedical applications. Glass-ceramic specimens were prepared by casting and heat treatment between 700 and 1200°C using a fast or a slow heating rate. The microstructure was characterized by atomic force microscopy and scanning electron microscopy. Crystalline phases were analyzed by x-ray diffraction. AFM of the as-cast glass revealed that amorphous phase separation occurred in this system. XRD confirmed the presence of fluorapatite in all specimens, together with forsterite and enstatite at higher temperatures. Both heating rate and heat treatment temperature strongly influenced microstructure and crystallinity. A dual microstructure with submicrometer fluorapatite crystals and polygonal forsterite crystals was obtained when slow heating rates and crystallization temperatures between 950 and 1100°C were used. Needle-shaped fluorapatite crystals appeared after heat treatment above 1100°C. Fast heating rates led to an increase in crystal size. Heat treatment temperatures should remain below 1100°C, together with slow heating rates, to prevent crystal dissolution, and preserve a dual microstructure of finely dispersed submicrometer crystals without growth of needle-shaped crystals.

  14. Near room temperature magnetodielectric consequence in (Li, Ti) doped NiO ceramic

    NASA Astrophysics Data System (ADS)

    Mukherjee, S.; Chatterjee, S.; Rayaprol, S.; Kaushik, S. D.; Bhattacharya, S.; Jana, P. K.

    2016-04-01

    In the quest for high-k dielectrics with decent magnetodielectric (MD) response, ball-milled processed (Li, Ti) doped NiO ceramics have been evaluated by various experimental techniques. Magnetic properties in these ceramics manifest with a pronounced anomaly appearing at ˜260 K, suggesting ferrimagnetic phase (related to cluster magnetism) and co-existence with a glassy-like antiferromagnetic phase at ˜7 K. Room temperature neutron diffraction pattern shows the existence of short-range magnetic correlations. In the magnetically ordered state below 250 K, the magnetic structure is found to be phase coexistence of G-type antiferromagnet and ferrimagnet. Impedance spectroscopy measurements over a wide temperature range can be perfectly described with appropriate microstructural model (internal barrier layer capacitor), based on domain and domain boundary relaxations, justifying the enhancement of the dielectric response. The low-temperature (T < 100 K) dielectric relaxation is polaronic in nature, associated with the charge ordering of a mixed valence states of Ti ions (co-existence of Ti3+ and Ti4+). Finally, our investigations in external magnetic fields up to 15 T reveal the occurrence of negative MD effect near room temperature. This intriguing intrinsic feature has been understood by the mechanism of charge-hopping-mediated MD effects.

  15. Effect of crystallization heat treatment on the microstructure of niobium-doped fluorapatite glass-ceramics

    PubMed Central

    Denry, I.; Holloway, J.A.; Gupta, P.K.

    2012-01-01

    Our goal was to study the effect of heat treatment temperature and heating rate on the microstructure and crystalline phases and assess the domain of existence of sub-micrometer fluorapatite crystals in niobium-doped fluorapatite glass-ceramics for biomedical applications. Glass-ceramic specimens were prepared by casting and heat treatment between 700 and 1200°C using a fast or a slow heating rate. The microstructure was characterized by atomic force microscopy and scanning electron microscopy. Crystalline phases were analyzed by x-ray diffraction. AFM of the as-cast glass revealed that amorphous phase separation occurred in this system. XRD confirmed the presence of fluorapatite in all specimens, together with forsterite and enstatite at higher temperatures. Both heating rate and heat treatment temperature strongly influenced microstructure and crystallinity. A dual microstructure with sub-micrometer fluorapatite crystals and polygonal forsterite crystals was obtained when slow heating rates and crystallization temperatures between 950 and 1100°C were used. Needle-shaped fluorapatite crystals appeared after heat treatment above 1100°C. Fast heating rates led to an increase in crystal size. Heat treatment temperatures should remain below 1100°C, together with slow heating rates, to prevent crystal dissolution, and preserve a dual microstructure of finely dispersed sub-micrometer crystals without growth of needle-shaped crystals. PMID:22454333

  16. Strontium doped lead zirconate titanate ceramics: study of calcination and sintering process to improve piezo effect.

    PubMed

    Khalid, Muhammad; Shoaib, Muhammad; Khan, Amir Azam

    2011-06-01

    Perovskite crystal structure is found in many ionic solids like CaTiO3, BaTiO3 and Lead Zirconate Titanates (PZT). In this structure off-center position of cations in oxygen octahedral causes polarization and produces direct and indirect piezoelectric responses in ceramic materials that are suitable for many ultrasonic applications. In the present study 9% Sr doped PZT ceramics were prepared and their dielectric and piezoelectric properties measured. X ray Diffraction (XRD) analysis of calcined powders demonstrated a decrease in the PbO content during the calcination stage at 850 degrees C. This was counterbalanced by adding excess PbO at the time of preparation of mixtures. Sintering was carried out at 1200 degrees C for 2 hours in lead rich atmosphere. The properties achieved were Dielectric Constant (K) = 1440, Tangent Loss (Tan delta) = 0.0062, Charge Coefficient (d33) = 335 pC/N and density = 7.55 g/cm3. SEM analysis of sintered samples demonstrated that grain size was 2-3 microm with clean grain boundaries and no large size porosity observed. XRD analysis of sintered pellets exhibited that material prepared was free of any precipitated phase usually harmful for the piezo effect.

  17. Thermal, structural and spectroscopic properties of heavy metal oxide glass and glass-ceramics doped with Er3+ ions

    NASA Astrophysics Data System (ADS)

    Ragin, Tomasz; Zmojda, Jacek; Kochanowicz, Marcin; Miluski, Piotr; Jelen, Piotr; Sitarz, Maciej; Dorosz, Dominik

    2015-09-01

    In this paper, bismuth-germanate oxide glass doped with erbium ions has been synthesized. Composition of the glass has been chosen in terms of the low phonon energy and good transparency in the infrared region. Transparent glass-ceramics sample has been prepared by controlled crystallization process. Fourier transform infrared spectroscopy (FTIR) has been used to determinate structural properties of samples. The absorption coefficient, the luminescence intensity in visible and infrared region and the differential scanning calorimetry have been examined. Difference in the emission intensity and shape of the luminescence bands indicates the presence of crystalline phases in obtained glass-ceramics sample.

  18. CeO2-covered nanofiber for highly efficient removal of phosphorus from aqueous solution.

    PubMed

    Ko, Young Gun; Do, Taegu; Chun, Youngsang; Kim, Choong Hyun; Choi, Ung Su; Kim, Jae-Yong

    2016-04-15

    The lowering phosphorus concentration of lakes or rivers using adsorbents has been considered to be the most effective way to prevent water eutrophication. However, the development of an adsorbent is still challenging because conventional adsorbents have not shown a sufficient phosphorus adsorption capacity (0.3-2.0mmol/g) to treat industrial, agricultural or domestic wastewater at a large scale. Herein, a novel and effective strategy to remove phosphorus efficiently with a CeO2-covered nanofiber is shown. The CeO2-covered nanofiber was synthesized through (1) amine group immobilization onto an electrospun polyacrylonitrile nanofiber and (2) adsorption of Ce(3+) on it. The CeO2-covered nanofiber played a role in catching phosphate ions in an aqueous solution by the oxidation, reduction, and ion-exchange of adsorbed Ce(3+) on the nanofiber from CeO2 to CePO4, and enabled remarkable phosphate adsorption capacity of the nanofiber (ca. 17.0mmol/g) at the range of ca. pH 2-6. Our strategy might be the most feasible method to efficiently lower the phosphorus concentration in lakes or rivers owing to the easy and inexpensive preparation of CeO2-covered nanofiber at an industrial scale, with a high phosphate adsorption capacity.

  19. CeO2-covered nanofiber for highly efficient removal of phosphorus from aqueous solution.

    PubMed

    Ko, Young Gun; Do, Taegu; Chun, Youngsang; Kim, Choong Hyun; Choi, Ung Su; Kim, Jae-Yong

    2016-04-15

    The lowering phosphorus concentration of lakes or rivers using adsorbents has been considered to be the most effective way to prevent water eutrophication. However, the development of an adsorbent is still challenging because conventional adsorbents have not shown a sufficient phosphorus adsorption capacity (0.3-2.0mmol/g) to treat industrial, agricultural or domestic wastewater at a large scale. Herein, a novel and effective strategy to remove phosphorus efficiently with a CeO2-covered nanofiber is shown. The CeO2-covered nanofiber was synthesized through (1) amine group immobilization onto an electrospun polyacrylonitrile nanofiber and (2) adsorption of Ce(3+) on it. The CeO2-covered nanofiber played a role in catching phosphate ions in an aqueous solution by the oxidation, reduction, and ion-exchange of adsorbed Ce(3+) on the nanofiber from CeO2 to CePO4, and enabled remarkable phosphate adsorption capacity of the nanofiber (ca. 17.0mmol/g) at the range of ca. pH 2-6. Our strategy might be the most feasible method to efficiently lower the phosphorus concentration in lakes or rivers owing to the easy and inexpensive preparation of CeO2-covered nanofiber at an industrial scale, with a high phosphate adsorption capacity. PMID:26795705

  20. Imaging the atomic surface structures of CeO2 nanoparticles

    SciTech Connect

    Lin, Yuyuan; Wu, Zili; Wen, Jianguo; Poeppelmeier, Kenneth R; Marks, Laurence D

    2014-01-01

    Atomic surface structures of CeO2 nanoparticles are under debate owing to the lack of clear experimental determination of the positions of the surface oxygen atoms. Particularly controversial is the (100) surface structure of this material. In this study, with oxygen atoms clearly observed using aberration corrected high resolution electron microscopy, we determined the atomic structures of the (100), (110) and (111) surfaces of CeO2 nanocubes. The predominantly exposed (100) surface has a mixture of Ce, O, and reduced CeO terminations, underscoring the complex structures of this polar surface that previously was often oversimplified. The (110) surface shows saw-like (111) nanofacets and flat CeO2-x terminations with oxygen vacancies. The (111) surface has an O termination. As these three low index surfaces are the most often exposed facets in the majority of CeO2 nanoparticles, these findings can be extended to the surfaces of differently shaped CeO2 nanoparticles as well as provide insight about face-selective catalysis.

  1. Dielectrical Properties of CeO2 Nanoparticles at Different Temperatures

    PubMed Central

    Zamiri, Reza; Abbastabar Ahangar, Hossein; Kaushal, Ajay; Zakaria, Azmi; Zamiri, Golnoosh; Tobaldi, David; Ferreira, J. M. F.

    2015-01-01

    A template-free precipitation method was used as a simple and low cost method for preparation of CeO2 nanoparticles. The structure and morphology of the prepared nanoparticle samples were studied in detail using X-ray diffraction, Raman spectroscopy and Scanning Electron Microscopy (SEM) measurements. The whole powder pattern modelling (WPPM) method was applied on XRD data to accurately measure the crystalline domain size and their size distribution. The average crystalline domain diameter was found to be 5.2 nm, with a very narrow size distribution. UV-visible absorbance spectrum was used to calculate the optical energy band gap of the prepared CeO2 nanoparticles. The FT-IR spectrum of prepared CeO2 nanoparticles showed absorption bands at 400 cm-1 to 450 cm-1 regime, which correspond to CeO2 stretching vibration. The dielectric constant (εr) and dielectric loss (tan δ) values of sintered CeO2 compact consolidated from prepared nanoparticles were measured at different temperatures in the range from 298 K (room temperature) to 623 K, and at different frequencies from 1 kHz to 1 MHz. PMID:25910071

  2. Characterization and properties of novel gallium-doped calcium phosphate ceramics.

    PubMed

    Mellier, Charlotte; Fayon, Franck; Schnitzler, Verena; Deniard, Philippe; Allix, Mathieu; Quillard, Sophie; Massiot, Dominique; Bouler, Jean-Michel; Bujoli, Bruno; Janvier, Pascal

    2011-09-01

    Addition of a gallium (Ga) precursor in the typical reaction protocols used for the preparation of β-tricalcium phosphate (β-TCP) led to novel Ga-doped β-TCP ceramics with rhombohedral structures (R3c space group). From the refinement of their X-ray diffraction patterns, it was found that the incorporation of Ga in the β-TCP network occurs by substitution of one of the five calcium (Ca) sites, while occupation of another Ca site decreases in inverse proportion to the Ga content in the structure. The Ga local environment and the modification of the phosphorus environments due to the Ga/Ca substitution in Ga-doped β-TCP compounds are probed using (31)P and (71)Ga magic-angle spinning NMR. A decrease of the unit cell volume is observed with increasing Ga content, together with improved mechanical properties. Indeed, the compressive strength of these new bioceramics is enhanced in direct proportion of the Ga content, up to a 2.6-fold increase as compared to pure β-TCP.

  3. Characterization and properties of novel gallium-doped calcium phosphate ceramics.

    PubMed

    Mellier, Charlotte; Fayon, Franck; Schnitzler, Verena; Deniard, Philippe; Allix, Mathieu; Quillard, Sophie; Massiot, Dominique; Bouler, Jean-Michel; Bujoli, Bruno; Janvier, Pascal

    2011-09-01

    Addition of a gallium (Ga) precursor in the typical reaction protocols used for the preparation of β-tricalcium phosphate (β-TCP) led to novel Ga-doped β-TCP ceramics with rhombohedral structures (R3c space group). From the refinement of their X-ray diffraction patterns, it was found that the incorporation of Ga in the β-TCP network occurs by substitution of one of the five calcium (Ca) sites, while occupation of another Ca site decreases in inverse proportion to the Ga content in the structure. The Ga local environment and the modification of the phosphorus environments due to the Ga/Ca substitution in Ga-doped β-TCP compounds are probed using (31)P and (71)Ga magic-angle spinning NMR. A decrease of the unit cell volume is observed with increasing Ga content, together with improved mechanical properties. Indeed, the compressive strength of these new bioceramics is enhanced in direct proportion of the Ga content, up to a 2.6-fold increase as compared to pure β-TCP. PMID:21793526

  4. Fabrication, spectral and laser performance of 5 at.% Yb3+ doped (La0.10Y0.90)2O3 transparent ceramic

    NASA Astrophysics Data System (ADS)

    Zhang, Haojia; Yang, Qiuhong; Lu, Shenzhou; Huang, Dongdong; Wang, Yonggang; Wei, Zhiyi; Wang, Qing; Zhang, Yongdong

    2013-02-01

    A 5 at.% Yb3+ doped (La0.10Y0.90)2O3 transparent ceramic was fabricated with nano-powders and sintered in H2 atmosphere. Spectroscopic properties and laser performance of Yb:(La0.10Y0.90)2O3 ceramic were studied. The ceramic exhibits excellent spectroscopic properties, with broad absorption and emission bands, and its refractive index (n) is close to 2. The gain cross-section (σg) was calculated at different population inversion ratio (β) values. In addition, among Yb3+ doped YAG crystal, Y2O3 and (YLa)2O3 ceramic, (YLa)2O3 ceramic has the least pump intensity (Imin) of 1.25 KW cm-2. Furthermore, a diode-pumped C-W ceramic laser output has been demonstrated at 1075 nm with a slope-efficiency of 60.2%.

  5. Zr doped anatase supported reticulated ceramic foams for photocatalytic water purification

    SciTech Connect

    Plesch, G.; Vargová, M.; Vogt, U.F.; Gorbár, M.; Jesenák, K.

    2012-07-15

    Highlights: ► Thick photocatalytic anatase films on macroporous reticulated ceramic foams. ► Alumina and alumina–mullite macroporous reticulated foams as photocatalyst support. ► Zr doping significantly improves the TiO{sub 2} film activity in phenol photomineralization. ► Comparison of photocatalytic activity of thick films and powder suspensions. -- Abstract: Titanium dioxide films were deposited on macroporous reticulated Al{sub 2}O{sub 3} and alumina–mullite foams with pore sizes of 15 ppi (pores per inch). Coatings were prepared from suspensions of precursor powders of Aeroxide{sup ®} P25 nanopowder and precipitated TiO{sub 2} by using a dip coating process. The TiO{sub 2} forms films with a thickness of ∼2–20 μm. The photocatalytic activity was characterized as the mineralization rate of an aqueous phenol solution under UVA irradiation by the TOC technique. Precipitated TiO{sub 2} films have nearly the same photocatalytic activity as a titania suspension, in which powder aggregates have a size comparable with the thickness of the films. Samples made of Aeroxide{sup ®} P25 nanopowder, in which the size of aggregates is ∼0.1 μm show higher efficiency of photodecomposition in suspensions with films. The doping of precipitated anatase with Zr(IV) in the atomic ratio Zr/Ti = 0.008 significantly improves the photocatalytic activity of the foam supported titania. Zr doped anatase films show better performance as the films prepared only from Aeroxide{sup ®} P25 nanopowder.

  6. Influence of CeO2 morphology on the catalytic activity of CeO2-Pt hybrids for CO oxidation.

    PubMed

    Singhania, Nisha; Anumol, E A; Ravishankar, N; Madras, Giridhar

    2013-11-21

    Ceria, because of its excellent redox behavior and oxygen storage capacity, is used as a catalyst for several technologically important reactions. In the present study, different morphologies of nano-CeO2 (rods, cubes, octahedra) were synthesized using the hydrothermal route. An ultrafast microwave-assisted method was used to efficiently attach Pt particles to the CeO2 polyhedra. These nanohybrids were tested as catalysts for the CO oxidation reaction. The CeO2/Pt catalyst with nanorods as the support was found to be the most active catalyst. XPS and IR spectroscopy measurements were carried out in order to obtain a mechanistic understanding and it was observed that the adsorbed carbonates with lower stability on the reactive planes of nanorods and cubes are the major contributor to this enhanced catalytic activity.

  7. Surface structure and catalytic properties of MoO3/CeO2 and CuO/MoO3/CeO2.

    PubMed

    Yu, Wujiang; Zhu, Jie; Qi, Lei; Sun, Chuanzhi; Gao, Fei; Dong, Lin; Chen, Yi

    2011-12-15

    XRD, LRS, TPR and in situ NH(3) adsorption FT-IR were used to investigate the dispersion state of the copper oxide and molybdena species of MoO(3)/CeO(2) and CuO/MoO(3)/CeO(2) catalysts as well as their surface acidity. The results showed that the molybdena monolayer modification promoted the dispersion of CuO due to the formation of new tetrahedral vacancies. Meanwhile, CuO changed the structure of molybdenum species and then influenced the surface acidity of the samples. A detail discussion about the possible model of the surface structure of the catalyst was presented. In addition, combining with the in situ NH(3) adsorption FT-IR, the relationships between the activities for ''NO + NH(3) + O(2)'' reaction and surface acid properties (Brønsted and Lewis acid sites) of the catalysts were discussed. PMID:21930282

  8. Simultaneous removal of elemental mercury and NO from flue gas by V2O5-CeO2/TiO2 catalysts

    NASA Astrophysics Data System (ADS)

    Zhang, Xunan; Li, Caiting; Zhao, Lingkui; Zhang, Jie; Zeng, Guangming; Xie, Yin'e.; Yu, Ming'e.

    2015-08-01

    A series of Ce-doped V2O5/TiO2 catalysts synthesized by an ultrasound assisted impregnation method were employed to investigate simultaneous removal of elemental mercury (Hg0) and NO in lab-scale experiments. Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), X-ray diffractogram (XRD), and X-ray photoelectron spectroscopy (XPS) analyses were used to characterize the samples. Compared to TiO2 support, the catalytic performance of CeO2 doped on both TiO2 and V2O5/TiO2 catalysts have been improved. Remarkably, 1%V2O5-10% CeO2/TiO2 (V1Ce10Ti) exhibited the highest Hg0 oxidation efficiency of 81.55% at 250 °C with a desired NO removal efficiency under the same condition. Both the NO conversion and Hg0 oxidation efficiency were enhanced in the presence of O2. The activity was inhibited by the injection of NH3 with the increase of NH3/NO. When in the presence of 400 ppm SO2, Hg0 oxidation was slightly affected. Furthermore, Hg0 removal behavior under both oxidation and selective catalytic reduction (SCR) condition over V1Ce10Ti were well investigated to further probe into the feasibility of one single unit for multi-pollutants control in industry application. The existence of the redox cycle of V4+ + Ce4+ ↔ V5+ + Ce3+ in V2O5-CeO2/TiO2 catalyst could not only greatly improve the NO conversion, but also promote the oxidation of Hg0.

  9. Structural, morphological, Raman, optical, magnetic, and antibacterial characteristics of CeO2 nanostructures

    NASA Astrophysics Data System (ADS)

    Abbas, Fazal; Iqbal, Javed; Jan, Tariq; Badshah, Noor; Mansoor, Qaisar; Ismail, Muhammad

    2016-01-01

    In this study, CeO2 nanostructures were synthesized by a soft chemical method. A hydrothermal treatment was observed to lead to an interesting morphological transformation of the nanoparticles into homogeneous microspheres composed of nanosheets with an average thickness of 40 nm. Structural analysis revealed the formation of a single-phase cubic fluorite structure of CeO2 for both samples. A Raman spectroscopic study confirmed the XRD results and furthermore indicated the presence of a large number of oxygen vacancies in the nanosheets. These oxygen vacancies led to room-temperature ferromagnetism (RTFM) of the CeO2 nanosheets with enhanced magnetic characteristics. Amazingly, the nanosheets exhibited substantially greater antibacterial activity than the nanoparticles. This greater antibacterial activity was attributed to greater exposure of high-surface-energy polar surfaces and to the presence of oxygen vacancies.

  10. Upconversion emission properties of CeO2: Tm3+, Yb3+ inverse opal photonic crystals

    NASA Astrophysics Data System (ADS)

    Cheng, Gong; Wu, Hangjun; Yang, Zhengwen; Liao, Jiayan; Lai, Shenfeng; Qiu, Jianbei; Song, Zhiguo

    2014-10-01

    The ordered and disordered templates were assembled by vertical deposition of polystyrene microspheres. The CeO2: Tm3+, Yb3+ precursor solution was used to infiltrate into the voids of the ordered and disordered templates, respectively. Then the ordered and disordered templates were calcined at 950°C in an air furnace, and the CeO2: Tm3+, Yb3+ inverse opals were obtained. The upconversion emissions from CeO2: Tm3+, Yb3+ inverse opals were suppressed due to the photon trapping caused by Bragg reflection of lattice planes when the upconversion emission band was in the range of the photonic band gaps in the inverse opals.

  11. First-principles characterization of formate and carboxyl adsorption on the stoichiometric CeO2(111) and CeO2(110) surfaces

    SciTech Connect

    Mei, Donghai

    2013-05-20

    Molecular adsorption of formate and carboxyl on the stoichiometric CeO2(111) and CeO2(110) surfaces was studied using periodic density functional theory (DFT+U) calculations. Two distinguishable adsorption modes (strong and weak) of formate are identified. The bidentate configuration is more stable than the monodentate adsorption configuration. Both formate and carboxyl bind at the more open CeO2(110) surface are stronger. The calculated vibrational frequencies of two adsorbed species are consistent with experimental measurements. Finally, the effects of U parameters on the adsorption of formate and carboxyl over both CeO2 surfaces were investigated. We found that the geometrical configurations of two adsorbed species are not affected by using different U parameters (U=0, 5, and 7). However, the calculated adsorption energy of carboxyl pronouncedly increases with the U value while the adsorption energy of formate only slightly changes (<0.2 eV). The Bader charge analysis shows the opposite charge transfer occurs for formate and carboxyl adsorption where the adsorbed formate is negatively charge whiled the adsorbed carboxyl is positively charged. Interestingly, with the increasing U parameter, the amount of charge is also increased. This work was supported by the Laboratory Directed Research and Development (LDRD) project of the Pacific Northwest National Laboratory (PNNL) and by a Cooperative Research and Development Agreement (CRADA) with General Motors. The computations were performed using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), which is a U.S. Department of Energy national scientific user facility located at PNNL in Richland, Washington. Part of the computing time was also granted by the National Energy Research Scientific Computing Center (NERSC)

  12. Dielectric Properties and AC Conduction of 5 wt % ZnBO Doped (Ba,Sr)TiO3 Ceramics for Low Temperature Co-fired Ceramics Applications

    NASA Astrophysics Data System (ADS)

    Kim, Se-Ho; Koh, Jung-Hyuk

    2009-04-01

    ZnBO doped (Ba0.5Sr0.5)TiO3 (BST) ceramic was synthesized by conventional mixed oxide method. 5 wt % ZnBO addition to the BST has lowered the sintering temperature of BST from 1350 to 1100 °C. From the X-ray diffraction analysis, we found that the 5 wt % ZnBO doped BST has the perovskite structure, and any pryo phase was not observed. The dielectric properties and ac conductivity have been investigated at temperature range from 30 to 130 °C with various frequencies (1-100 kHz). The real part of relative dielectric permittivity ɛr' was decreased with increasing the temperature and the frequency. The activation energy for conduction process was calculated from the slope of ac conductivity at 1 kHz. The activation energy calculated through the Arrhenius law was 0.42 eV. In this paper, we will discuss the low-frequency dielectric relaxation and ac conductivity of 5 wt % ZnBO doped BST ceramics in relation to the electrical conduction.

  13. Highly Efficient Tm-Doped Yttrium Aluminum Garnet Ceramic Laser Based on the Novel Fiber-Bulk Hybrid Configuration

    NASA Astrophysics Data System (ADS)

    Liu, Jun; Shen, Deyuan; Huang, Haitao; Zhang, Xiaoqi; Tang, Dingyuan; Fan, Dianyuan

    2013-09-01

    A polycrystalline ceramic Tm3+-doped yttrium aluminum garnet (Tm:Y3Al5O12, Tm:YAG) laser based on the novel fiber-bulk hybrid configuration is demonstrated using a high-power and tunable Er,Yb co-doped fiber laser as the pump source. Lasing characteristics of a 4.0 at. % Tm:YAG ceramic are investigated at different pump wavelengths from 1617 to 1625 nm. With an output coupler of 10% transmission, a maximum output power of 3.9 W is obtained at 2013.2 nm under an 8.8 W incident pump power at the Tm:YAG absorption peak of 1620.4 nm, corresponding to a slope efficiency of 50.1% with respect to the incident pump power.

  14. Effects of pH and phosphate on CeO2 nanoparticle dissolution.

    PubMed

    Dahle, Jessica T; Livi, Ken; Arai, Yuji

    2015-01-01

    As the result of rapidly grown nanotechnology industries, release of engineered nanoparticles (ENPs) to environment has increased, posing in a serious risk to environmental and human health. To better understand the chemical fate of ENPs in aquatic environments, solubility of CeO2 NPs was investigated using batch dissolution experiments as a function of pH (1.65-12.5), [phosphate] and particle size (33 and 78 nm). It was found that CeO2 dissolution was only significant at pH<5 and inversely proportional to surface area. After 120 h, the release of Ce was ∼3 times greater in large NPs than that in small NPs that is likely contributed by the difference in exchangeable Ce(III) impurity (small: 0.3 mM kg(-1), large: 1.56 mM kg(-1)). When 100 μM of phosphate was added, the dissolution rate of CeO2 NPs was decreased in small NPs by 15% at pH 1.65 and 75% at pH 4.5 and in large NPs by 56% at pH 1.65 and 63% at pH 4.5. The inner-sphere surface complexation of P that is revealed by the zeta potential measurements is effectively suppressing the CeO2 NP dissolution. Predicting the fate and transport of CeO2 NPs in aquatic environment, pH and P ligands might play important roles in controlling the solubility of CeO2 NPs.

  15. Transmission Electron Microscopy Investigation of Krypton Bubbles in Polycrystalline CeO2

    SciTech Connect

    Lingfeng He; Clarissa Yablinsky; Mahima Gupta; Jian Gan; Marquis A. Kirk; Todd R. Allen

    2013-05-01

    To gain an understanding of gas bubble transport in oxide nuclear fuel, this paper uses polycrystalline CeO2, composed of both nanograins and micrograins, as a surrogate material for UO2. The CeO2 was implanted with 150-keV Kr ions up to a dose of 1 x 1016 ions/cm2 at 600 degrees C. Transmission electron microscopy characterizations of small Kr bubbles in nanograin and micrograin regions were compared. The grain boundary acted as an efficient defect sink, as evidenced by smaller bubbles and a lower bubble density in the nanograin region as compared to the micrograin region.

  16. Conversion of Acetic Acid from the Catalytic Pyrolysis of Xylan Over CeO2.

    PubMed

    Lee, Heejin; Ko, Jeong Huy; Kwon, Woo Hyun; Park, Young-Kwon

    2016-05-01

    CeO2 was synthesized hydrothermally in supercritical water and applied to the catalytic pyrolysis of xylan. Acetic acid, which is the main component in bio-oil produced from the non-catalytic pyrolysis of xylan, deteriorates the fuel quality of the oil. Catalysis over CeO2 effectively converted the acetic acid to ketone species, such as acetone, thereby reducing the acidity of the oil considerably. The content of aromatics in bio-oil was also increased substantially by catalysis. PMID:27483777

  17. Current-voltage characteristics and grain growth of Li{sub 2}CO{sub 3}-doped tungsten trioxide ceramics

    SciTech Connect

    Wang, Y.; Yang, X.S.; Li, Z.Q.; Yao, K.L.; Liu, Z.L

    2004-08-03

    Ceramics samples of tungsten trioxide doped with lithium carbonate from 0.5 to 5 mol% were prepared by conventional electroceramic technique. The current-voltage characteristics of these ceramics were measured under various ambient temperatures. All of the I-V curves showed non-ohmic electrical properties with obvious negative-resistance characteristic at room temperature. It is found that there exists a direct correlation between the negative-resistance phenomenon in the I-V curves and the electrical history of these samples. The suitability of some models regarding the negative-resistance characteristics is discussed. X-ray diffraction (XRD) revealed coexistence of two phases of tungsten trioxide, which depends on the amount of lithium. Scanning electron microscope (SEM) showed great differences for both grain shape and size between the Li-doped and undoped WO{sub 3} ceramics, and this indicates that Li{sub 2}CO{sub 3} doped into WO{sub 3} influences strongly the growing of WO{sub 3} during sintering process.

  18. Tunable Magnetic Properties in CuCr2- x Fe x O4 Ceramics by Doping of Fe

    NASA Astrophysics Data System (ADS)

    Zhu, C. M.; Wang, L. G.; Bao, D. L. G. C.; Luo, H.; Tian, Z. M.; Yuan, S. L.

    2016-08-01

    CuCr2- x Fe x O4 ceramics have been successfully synthesized using the sol-gel method for the first time. With pure formation, material structure has been characterized by x-ray diffraction. The samples have been identified as having the spinel structure with formulae CuCr2- x Fe x O4. Micrographs obtained by scanning electron microscopy show the dense microstructure of the samples. The stoichiometric ratio of the ceramics has been measured through energy dispersive spectra. Magnetic properties of CuCr2- x Fe x O4 ceramics have been discussed. Temperature dependence of magnetization presents the gradually increasing irreversible temperature as the content of Fe element increases from x = 0 to 1. Coercive field ( H C), remanent magnetization ( M r), and saturation magnetization ( M S) respectively display the monotonous variation phenomena with increasing content of Fe. The increasing M r, M S and the decreasing H C can be attributed to the change of magnetic exchange interaction because of the doped Fe. It also proves that the magnetic properties of CuCr2- x Fe x O4 ceramics can be effectively tuned by the doping content of Fe.

  19. Polarity driven morphology of CeO2(1 0 0) islands on Cu(1 1 1)

    NASA Astrophysics Data System (ADS)

    Stetsovych, O.; Beran, J.; Dvořák, F.; Mašek, K.; Mysliveček, J.; Matolín, V.

    2013-11-01

    Thin ceria films supported by metal substrates represent important model systems for reactivity studies in heterogeneous catalysis. Here we report the growth study of the polar CeO2(1 0 0) phase as part of a mixed CeO2(1 1 1)-CeO2(1 0 0) thin film supported by Cu(1 1 1). The two ceria phases grow on different areas of the substrate, what allows a reliable growth characterization of the CeO2(1 0 0) islands on Cu(1 1 1). Scanning tunneling microscopy measurements reveal CeO2(1 0 0) to grow in the form of highly dispersed three dimensional (3D) islands on a CeO2(1 0 0) interfacial layer. The CeO2(1 0 0) islands exhibit a 2 × 2 surface reconstruction. The presence of the surface reconstruction together with the highly dispersed growth of CeO2(1 0 0) islands corresponds to the requirement for compensation of the surface dipole moment on the CeO2(1 0 0). CeO2(1 0 0) islands are further characterized by reflection high energy electron diffraction yielding their epitaxial relations with respect to the Cu(1 1 1) substrate. The growth of well characterized CeO2(1 0 0) islands supported by Cu(1 1 1) represents a starting point for developing a novel template for structure-related reactivity studies of ceria based model catalysts.

  20. Progress in rare-earth-doped nanocrystalline glass-ceramics for laser cooling

    NASA Astrophysics Data System (ADS)

    Venkata Krishnaiah, Kummara; Ledemi, Yannick; Soares de Lima Filho, Elton; Loranger, Sebastien; Nemova, Galina; Messaddeq, Younes; Kashyap, Raman

    2016-03-01

    Laser cooling with anti-Stokes fluorescencewas predicted by Pringsheim in 1929, but for solids was only demonstrated in 1995. There are many difficulties which have hindered laser assisted cooling, principally the chemical purity of a sample and the availability of suitable hosts. Recent progress has seen the cooled temperature plummet to 93K in Yb:YLF. One of the challenges for laser cooling to become ubiquitous, is incorporating the rare-earthcooling ion in a more easily engineered material, rather than a pure crystalline host. Rare-earth-doped nanocrystalline glass-ceramics were first developed by Wang and Ohwaki for enhanced luminescence and mechanical properties compared to their parent glasses. Our work has focused on creating a nanocrystalline environment for the cooling ion, in an easy to engineer glass. The glasses with composition 30SiO2-15Al2O3-27CdF2-22PbF2-4YF3-2YbF3 (mol%), have been prepared by the conventional melt-quenching technique. By a simple post fabrication thermal treatment, the rare-earth ions are embedded in the crystalline phase within the glass matrix. Nanocrystals with various sizes and rare-earth concentrations have been fabricated and their photoluminescence properties assessed in detail. These materials show close to unity photoluminescence quantum yield (PLQY) when pumped above the band. However, they exhibit strong up-conversion into the blue, characteristic of Tm trace impurity whose presence was confirmed. The purification of the starting materials is underway to reduce the background loss to demonstrate laser cooling. Progress in the development of these nano-glass-ceramics and their experimental characterization will be discussed.

  1. Wavelength tunability of laser based on Yb-doped YGAG ceramics

    NASA Astrophysics Data System (ADS)

    Šulc, Jan; Jelínková, Helena; Jambunathan, Venkatesan; Miura, Taisuke; Endo, Akira; Lucianetti, Antonio; Mocek, TomáÅ.¡

    2015-02-01

    The wavelength tunability of diode pumped laser based on Yb-doped mixed garnet Y3Ga2Al3O12 (Yb:YGAG) ceramics was investigated. The tested Yb:YGAG sample (10% Yb/Y) was in the form of 2mm thick plane-parallel face-polished plate (without AR coatings). A fiber (core diameter 100 μm, NA= 0.22) coupled laser diode (LIMO, LIMO35-F100-DL980-FG-E) with emission at wavelength 969 nm, was used for longitudinal Yb:YGAG pumping. The laser diode was operating in the pulsed regime (2 ms pulse length, 10 Hz repetition rate). The duty-cycle 2% ensured a low thermal load even under the maximum diode pumping power amplitude 20W (ceramics sample was only air-cooled). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.01 - 1.09 μm, HT @ 0.97 μm) and curved (r = 150mm) output coupler with a reflectivity of ˜ 97% @ 1.01 - 1.09 μm. Wavelength tuning of the ytterbium laser was accomplished by using a birefringent filter (single 1.5mm thick quartz plate) placed inside the optical resonator at the Brewster angle between the output coupler and the laser active medium. The laser was continuously tunable over ˜ 58nm (from 1022nm to 1080 nm) and the tuning band was mostly limited by the free spectral range of used birefringent filter. The maximum output power amplitude 3W was obtained at wavelength 1046nm for absorbed pump power amplitude 10.6W. The laser slope efficiency was 34%.

  2. Piezoelectric Properties of CuO-Doped (K,Na)NbO3 Lead-Free Ceramics Synthesized with Hydrothermal Powders

    NASA Astrophysics Data System (ADS)

    Yokouchi, Yuriko; Maeda, Takafumi; Bornmann, Peter; Hemsel, Tobias; Morita, Takeshi

    2013-07-01

    We report the piezoelectric properties of CuO-doped hydrothermal (K,Na)NbO3 ceramics that can be applied as hard-type lead-free piezoelectric ceramics. To date, we have succeeded in synthesizing high-quality KNbO3 and NaNbO3 powders by the hydrothermal method, which is based on an ionic reaction at high temperature (around 210 °C) and pressure. Increasing both the piezoelectric constant d and the mechanical quality factor (Qm) is important for resonance-type piezoelectric devices, such as ultrasonic motors and transformers. CuO doping into hydrothermal (K,Na)NbO3 ceramics was examined to realize hard-type lead-free piezoelectric ceramics. By doping with 1.2 mol % CuO, Qm was increased and the dielectric loss (tan δ) was decreased to 0.5%. The grain size was also influenced by the amount of CuO doping, which indicates that Qm is related to the density. To achieve a higher Qm value, the grain size is required to be less than 5 µm however, excessive CuO doping leads to anomalous grain growth. Optimal piezoelectric properties were obtained for 1.2 mol % CuO-doped (K,Na)NbO3; k31 = 0.32, d31 = -44 pC/N, Qm (radial) = 959, and tan δ= 0.5%. These characteristics showed that CuO doping with hydrothermal powders is effective for obtaining hard-type ceramics, and the mechanical quality factor is more than ten times higher than that of nondoped hydrothermal (K,Na)NbO3 ceramics. Therefore, compared with the conventional solid-state method, we could succeed in obtaining hard-type ceramics by a simple and short process.

  3. Structural and Luminescence Properties of Sm(3+) Doped TTB -Type BaTa2O6 Ceramic Phosphors.

    PubMed

    Ekmekçi, Mete Kaan; İlhan, Mustafa; Başak, Ali Sadi; Deniz, Sabahattin

    2015-11-01

    Pure and 0.5 to 10 mole% Sm(3+) doped TTB (tetragonal tungsten bronze)-type BaTa2O6 ceramic phosphor was produced by the solid state reaction method which performed at 1425 °C for 20 h. XRD and SEM analysis indicated single TTB phase for undoped and 0.5 to 10 mole% Sm(3+) doped BaTa2O6 structures. SEM also showed that the BaTa2O6 grain size decreased with the increasing content of Sm(3+). Optical analysis indicated significant emissions in the visible spectral region as green (λ = 562.7 nm) and orange-reddish (λ = 597.1 nm). The emission intensity increased with the increasing doping concentration up to 2.5 mole%, and then decreased due to the concentration quenching effect.

  4. Formation of CeO 2 buffer layer using multi-plume PLD

    NASA Astrophysics Data System (ADS)

    Sutoh, Y.; Nakaoka, K.; Miura, M.; Matsuda, J.; Nakanishi, T.; Nakai, A.; Yoshizumi, M.; Izumi, T.; Miyata, S.; Iijima, Y.; Yamada, Y.; Shiohara, Y.; Saitoh, T.

    2008-09-01

    The CeO 2 buffer layer was fabricated using the multi-plume pulsed laser deposition (PLD) method with different deposition rates controlled by the excimer laser energy and frequency on the Gd 2Zr 2O 7 template tape formed by the ion-beam assisted deposition (IBAD) with 14° of Δ φ (full width at half maximum (FWHM) value of X-ray diffraction φ-scan for Gd 2Zr 2O 7 (2 2 2) pole). The laser conditions with high pulse energy and low frequency resulted in a highly textured in-plane grain alignment (Δ φ). The surface roughness and Δ φ values were improved by increasing the thickness of the CeO 2 buffer layer. YBCO films with the thickness of 1 μm and 1.6 μm were further deposited by the advanced trifluoroacetates-metal organic deposition (TFA-MOD) on the CeO 2 buffered substrates with the deposition rate of 0.15 and 0.5 μm/min. The Jc values of 2.5 MA/cm 2 and 2 MA/cm 2 were obtained, respectively. High Jc films could be deposited on the CeO 2 buffer layer even at high deposition rate by the multi-plume deposition.

  5. Fundamentals and Catalytic Applications of CeO2-Based Materials.

    PubMed

    Montini, Tiziano; Melchionna, Michele; Monai, Matteo; Fornasiero, Paolo

    2016-05-25

    Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40(th) anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are deepening our understanding of these materials, helping us to predict their behavior and application potential. This review has a wide view on all those aspects related to ceria which promise to produce an important impact on our life, encompassing fundamental knowledge of CeO2 and its properties, characterization toolbox, emerging features, theoretical studies, and all the catalytic applications, organized by their degree of establishment on the market.

  6. Antimicrobial potential of green synthesized CeO2 nanoparticles from Olea europaea leaf extract

    PubMed Central

    Maqbool, Qaisar; Nazar, Mudassar; Naz, Sania; Hussain, Talib; Jabeen, Nyla; Kausar, Rizwan; Anwaar, Sadaf; Abbas, Fazal; Jan, Tariq

    2016-01-01

    This article reports the green fabrication of cerium oxide nanoparticles (CeO2 NPs) using Olea europaea leaf extract and their applications as effective antimicrobial agents. O. europaea leaf extract functions as a chelating agent for reduction of cerium nitrate. The resulting CeO2 NPs exhibit pure single-face cubic structure, which is examined by X-ray diffraction, with a uniform spherical shape and a mean size 24 nm observed through scanning electron microscopy and transmission electron microscopy. Ultraviolet-visible spectroscopy confirms the characteristic absorption peak of CeO2 NPs at 315 nm. Fourier transform infrared spectroscopy reflects stretching frequencies at 459 cm−1, showing utilization of natural components for the production of NPs. Thermal gravimetric analysis predicts the successful capping of CeO2 NPs by bioactive molecules present in the plant extract. The antimicrobial studies show significant zone of inhibition against bacterial and fungal strains. The higher activities shown by the green synthesized NPs than the plant extract lead to the conclusion that they can be effectively used in biomedical application. Furthermore, reduction of cerium salt by plant extract will reduce environmental impact over chemical synthesis. PMID:27785011

  7. Ionic liquid-assisted sonochemical preparation of CeO2 nanoparticles for CO oxidation

    DOE PAGESBeta

    Alammar, Tarek; Noei, Heshmat; Wang, Yuemin; Grünert, Wolfgang; Mudring, Anja -Verena

    2014-10-10

    CeO2 nanoparticles were synthesized via a one-step ultrasound synthesis in different kinds of ionic liquids based on bis(trifluoromethanesulfonylamide, [Tf2N]–, in combination with various cations including 1-butyl-3-methylimidazolium ([C4mim]+), 1-ethyl-2,3-dimethylimidazolium ([Edimim]+), butyl-pyridinium([Py4]+), 1-butyl-1-methyl-pyrrolidinium ([Pyrr14]+), and 2-hydroxyethyl-trimethylammonium ([N1112OH]+). Depending on synthetic parameters, such as ionic liquid, Ce(IV) precursor, heating method, and precipitator, formed ceria exhibits different morphologies, varying from nanospheres, nanorods, nanoribbons, and nanoflowers. The morphology, crystallinity, and chemical composition of the obtained materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and N2 adsorption. The structural and electronic propertiesmore » of the as-prepared CeO2 samples were probed by CO adsorption using IR spectroscopy under ultrahigh vacuum conditions. The catalytic activities of CeO2 nanoparticles were investigated in the oxidation of CO. CeO2 nanospheres obtained sonochemically in [C4mim][Tf2N] exhibit the best performance for low-temperature CO oxidation. As a result, the superior catalytic performance of this material can be related to its mesoporous structure, small particle size, large surface area, and high number of surface oxygen vacancy sites.« less

  8. Fate of cerium dioxide (CeO2) nanoparticles in municipal wastewater during activated sludge treatment.

    PubMed

    Gómez-Rivera, Francisco; Field, James A; Brown, Dustin; Sierra-Alvarez, Reyes

    2012-03-01

    This study investigated the fate of nano-CeO(2) during municipal wastewater treatment using a laboratory-scale activated sludge (A/S) system fed with primarily-treated municipal wastewater and nano-CeO(2) (55.0 mg Ce/L). Nano-CeO(2) was highly removed during A/S treatment (96.6% total Ce). Extensive removal of CeO(2) <200 nm was also attained and the concentration escaping treatment was only 0.11 mg Ce/L. Elimination occurred mainly by aggregation and settling of CeO(2) particles, promoted by circumneutral pH values and by nanoparticle interactions with organic and/or inorganic wastewater constituents. Biosorption also contributed to CeO(2) removal as shown by sludge analysis and batch adsorption studies. Batch bioassays demonstrated that nano-CeO(2) only exerted inhibition of O(2) uptake by A/S at concentrations exceeding those in the bioreactor feed (50% inhibition at 950 mg CeO(2)/L). These findings indicate that A/S treatment is expected to provide extensive removal of nano-CeO(2) in municipal wastewaters.

  9. Sensor properties of the nanostructured In2O3-CeO2 system in detection of reducing gases

    NASA Astrophysics Data System (ADS)

    Gerasimov, G. N.; Gromov, V. F.; Trakhtenberg, L. I.; Belysheva, T. V.; Spiridonova, E. Yu.; Rozenbaum, V. M.

    2014-03-01

    The sensor properties of nanostructured In2O3-CeO2 composite films with different compositions in hydrogen and carbon monoxide detection in air in the temperature range 280-500°C were studied. The temperature curves of the sensor effect S have a shape typical for metal oxide sensors with maxima S max at definite temperatures Tmax. The maxima characterize the sensor properties of the films and increased considerably when small amounts of CeO2 were added to In2O3. The highest sensitivity was found in composite films with 3-10 wt % CeO2. When the composite was further enriched with ceric oxide, the sensitivity decreased; at 40 wt % CeO2 it was considerably lower than that of pure In2O3. The introduction of CeO2 in In2O3 also caused a shift of Tmax toward lower temperatures. The mechanism of the sensitivity of the In2O3-CeO2 composite was considered; it includes the promotion of sensor reactions by small CeO2 nanoclusters lying on the surface of In2O3 crystals and an electron transfer from In2O3 to CeO2.

  10. An Evaluation of the Potential Phototoxicity of CeO2 Nanoparticles in Retinal Pigment Epithelial Cells in-vitro

    EPA Science Inventory

    Cerium dioxide (CeO2) engineered nanoparticles (NP) are used as fuel-borne catalysts in off-road diesel engines, which can lead to exhaust emissions of respirable CeO2 NP. Other metal oxides may act as photo-catalysts which induce the generation of free radicals upon exposure to ...

  11. Enhanced Colloidal Stability of CeO2 Nanoparticles by Ferrous Ions: Adsorption, Redox Reaction, and Surface Precipitation.

    PubMed

    Liu, Xuyang; Ray, Jessica R; Neil, Chelsea W; Li, Qingyun; Jun, Young-Shin

    2015-05-01

    Due to the toxicity of cerium oxide (CeO2) nanoparticles (NPs), a better understanding of the redox reaction-induced surface property changes of CeO2 NPs and their transport in natural and engineered aqueous systems is needed. This study investigates the impact of redox reactions with ferrous ions (Fe2+) on the colloidal stability of CeO2 NPs. We demonstrated that under anaerobic conditions, suspended CeO2 NPs in a 3 mM FeCl2 solution at pH 4.8 were much more stable against sedimentation than those in the absence of Fe2+. Redox reactions between CeO2 NPs and Fe2+ lead to the formation of 6-line ferrihydrite on the CeO2 surfaces, which enhanced the colloidal stability by increasing the zeta potential and hydrophilicity of CeO2 NPs. These redox reactions can affect the toxicity of CeO2 NPs by increasing cerium dissolution, and by creating new Fe(III) (hydr)oxide reactive surface layers. Thus, these findings have significant implications for elucidating the phase transformation and transport of redox reactive NPs in the environment.

  12. On the mechanism of nanoparticulate CeO2 toxicity to freshwater algae.

    PubMed

    Angel, Brad M; Vallotton, Pascal; Apte, Simon C

    2015-11-01

    The factors affecting the chronic (72-h) toxicity of three nanoparticulate (10-34nm) and one micron-sized form of CeO2 to the green alga, Pseudokirchneriella subcapitata were investigated. To characterise transformations in solution, hydrodynamic diameters (HDD) were measured by dynamic light scatter, zeta potential values by electrophoretic mobility, and dissolution by equilibrium dialysis. The protective effects of humic and fulvic dissolved organic carbon (DOC) on toxicity were also assessed. To investigate the mechanisms of algal toxicity, the CytoViva hyperspectral imaging system was used to visualise algal-CeO2 interactions in the presence and absence of DOC, and the role of reactive oxygen species (ROS) was investigated by 'switching off' ROS production using UV-filtered lighting conditions. The nanoparticulate CeO2 immediately aggregated in solution to HDDs measured in the range 113-193nm, whereas the HDD and zeta potential values were significantly lower in the presence of DOC. Negligible CeO2 dissolution over the time course of the bioassay ruled out potential toxicity from dissolved cerium. The nanoparticulate CeO2 concentration that caused 50% inhibition of algal growth rate (IC50) was in the range 7.6-28mg/L compared with 59mg/L for micron-sized ceria, indicating that smaller particles were more toxic. The presence of DOC mitigated toxicity, with IC50s increasing to greater than 100mg/L. Significant ROS were generated in the nanoparticulate CeO2 bioassays under normal light conditions. However, 'switching off' ROS under UV-filtered light conditions resulted in a similar IC50, indicating that ROS generation was not the toxic mechanism. The CytoViva imaging showed negligible sorption of nanoparticulate CeO2 to algal cells in the presence of DOC, and strong sorption in its absence, suggesting that this was the toxic mechanism. The results suggest that DOC in natural waters will coat CeO2 particles and mitigate toxicity to algal cells.

  13. Leaching effect in gadolinia-doped ceria aqueous suspensions for ceramic processes

    NASA Astrophysics Data System (ADS)

    Caldarelli, A.; Mercadelli, E.; Presto, S.; Viviani, M.; Sanson, A.

    2016-09-01

    Gadolinium doped ceria (CGO) is a commonly used electrolytic material for Solid Oxide Fuel Cells (SOFCs) and for this reason different shaping methods for its deposition are reported in literature. Most of these processes are based on the use of organic-based CGO suspensions, but water-based processes are acquiring increasingly interest for their economical and environmental friendly properties. In this paper we reported how the components of water-based suspension and some unexpected process parameters can deeply affect the functional properties of the final powder. In particular, we observed that CGO powders are strongly affected by ionic leaching induced by furoic acid used as dispersant: the extent of this leaching was related to the dispersant concentration and suspension's ball-milling-time; the phenomenon was confirmed by ICP-AES analyses on suspensions surnatant. Most importantly, ionic leaching affected the electrical properties of CGO: leached powder showed a higher ionic conductivity as a consequence of a partial removal of Gd ions at the grain boundaries. This work is therefore pointing out that when considering water-based suspensions, it is extremely important to carefully consider all the process parameters, including the organic components of the ceramic suspension, as these could lead to unexpected effects on the properties of the powder, affecting the performance of the final shaped material.

  14. Preliminary evaluation of therapeutic ion release from Sr-doped zinc-silicate glass ceramics.

    PubMed

    Looney, Mark; O'Shea, Helen; Boyd, Daniel

    2013-01-01

    Bioactive and degradable porous bioceramics play an important role in many clinical situations. Porosity is essential to the performance of a material that is proposed to be used as an implantable osseous scaffold. Scaffolds provide a three dimensional support and template to osseous integration and vascularization. Combining the porosity of a scaffold with the ability of the scaffold material to deliver therapeutic ions to the site of implantation goes some way towards developing an ideal bone graft. A series of strontium-doped zinc silicate (Ca-Sr-Na-Zn-Si) glass ceramics scaffoldswere developed, whose porosity was measured to be between 93% and 96%, which is advantageous in terms of osseous integration and vascularization. The levels of Zn(2+) and Sr(2+) detected as a result of degradation of the crystalline phases were found to be 1.4-600 parts per million (ppm) and 0-583 ppm, respectively. The levels detected correlate well with the levels of Sr(2+) and Zn(2+)ions typically associated with clinical benefits, including antibacterial efficacy, osteoblastic differentiation and impaired osteoclastic resorption.

  15. Anomalous dielectric and thermal properties of Ba-doped PbZrO3 ceramics.

    PubMed

    Pirc, R; Rožič, B; Koruza, J; Cordoyiannis, G; Malič, B; Kutnjak, Z

    2015-11-18

    The dielectric and thermal properties of an antiferroelectric (AFE) material characterised by an intermediate ferroelectric (FE) phase between the AFE and paraelectric phase in zero field are studied by means of a generalised Landau-Kittel model of AFEs. A temperature-dependent coupling of the two sublattices is introduced in accordance with the Rae-Dove (RD) model of re-entrant phase transitions. The sublattice polarisation components are calculated as functions of temperature and the applied electric field by minimising numerically the free energy. The calculated dielectric susceptibility shows anomalies at the boundaries of the intermediate FE phase, characteristic for first-order phase transitions. It is shown that this behaviour is in qualitative agreement with the measured dielectric constant in Ba-doped PbZrO3 ceramics. The model also predicts a negative adiabatic electrocaloric temperature change ΔT in a broad temperature range in the AFE phase, in qualitative agreement with experiments. The dipolar heat capacity is also predicted to be negative in the intermediate phase in zero field, in analogy with the results of the RD model. PMID:26490797

  16. Anomalous dielectric and thermal properties of Ba-doped PbZrO3 ceramics

    NASA Astrophysics Data System (ADS)

    Pirc, R.; Rožič, B.; Koruza, J.; Cordoyiannis, G.; Malič, B.; Kutnjak, Z.

    2015-11-01

    The dielectric and thermal properties of an antiferroelectric (AFE) material characterised by an intermediate ferroelectric (FE) phase between the AFE and paraelectric phase in zero field are studied by means of a generalised Landau-Kittel model of AFEs. A temperature-dependent coupling of the two sublattices is introduced in accordance with the Rae-Dove (RD) model of re-entrant phase transitions. The sublattice polarisation components are calculated as functions of temperature and the applied electric field by minimising numerically the free energy. The calculated dielectric susceptibility shows anomalies at the boundaries of the intermediate FE phase, characteristic for first-order phase transitions. It is shown that this behaviour is in qualitative agreement with the measured dielectric constant in Ba-doped PbZrO3 ceramics. The model also predicts a negative adiabatic electrocaloric temperature change Δ T in a broad temperature range in the AFE phase, in qualitative agreement with experiments. The dipolar heat capacity is also predicted to be negative in the intermediate phase in zero field, in analogy with the results of the RD model.

  17. Growth-Rate Induced Epitaxial Orientation of CeO2 on Al2O3(0001)

    SciTech Connect

    Kuchibhatla, Satyanarayana V N T; Nachimuthu, Ponnusamy; Gao, Fei; Jiang, Weilin; Shutthanandan, V.; Engelhard, Mark H.; Seal, Sudipta; Thevuthasan, Suntharampillai

    2009-05-19

    High-quality ceria (CeO2) films were grown on sapphire (Al2O3) (0001) substrates using oxygen plasma-assisted molecular beam epitaxy. The epitaxial orientation of the ceria films has been found to be (100) and (111) at low (< 8 Å/min) and higher growth rates (up to ~30 Å/min), respectively. Evidence shows that CeO2 (100) film grows as three-dimensional islands, while CeO2 (111) proceeds with layered growth. Three in-plane domains at 30° to each other are observed in the CeO2 (100), which is attributed to the close match of the oxygen sub-lattices in the film and substrate that has a three-fold symmetry. Molecular dynamic simulations have further confirmed that the CeO2 film retains (100) orientation on the Al2O3 (0001) substrate.

  18. Controlling polymorphic structures and investigating electric properties of Ca-doped zirconia using solid state ceramic method

    SciTech Connect

    Emam, W.I.; Mabied, Ahmed F.; Hashem, H.M.; Selim, M.M.; El-Shabiny, A.M.; Ahmed Farag, I.S.

    2015-08-15

    Structural study of Zr{sub 1−x}Ca{sub x}O{sub 2−x} samples with x=0.01–0.15 were prepared using solid state ceramic method. X-ray diffraction analysis revealed a mixture of the high temperature phase and the monoclinic one for the samples with x≤0.05. On the other hand, the formation of a single high temperature cubic phase was observed within a concentration range of x=0.06–0.10. At concentrations higher than 0.10 the calcium zirconate phase was observed besides the dominant high temperature one. Rietveld refinement of the single phase data clearly revealed, that substitution of zirconium by calcium increases both the lattice parameters as well as the tetrahedral bond length. Ionic to electronic conductivity ratio enhanced considerably as Ca-doping level ascends. The dielectric constant shows strong temperature dependence at lower frequencies. The dielectric loss factor increases rapidly with the increase in temperature at lower frequencies, while decreases with the increase in frequency at higher temperatures. The ionic conduction is considered as the dominant process at higher temperatures. - Graphical abstract: Forming a high temperature cubic zirconia phase at 1200 °C using ceramic solid state method and aliovalent cation. - Highlights: • Formation the high temperature cubic polymorph of zirconia using Ca-doping. • Solid state ceramic method was used for preparing the cubic Ca-doped zirconia. • Substitution of zirconium by calcium increases the lattice parameters and the bond length. • Ionic to electronic conductivity ratio enhanced considerably as Ca-doping level increases.

  19. Fundamental Understanding of the Interaction of Acid Gases with CeO2 : From Surface Science to Practical Catalysis

    DOE PAGESBeta

    Tumuluri, Uma; Rother, Gernot; Wu, Zili

    2016-03-21

    Acid gases including CO2, SO2, and NOx are ubiquitous in large-scale energy applications including heterogeneous catalysis. The adverse environmental and health effects of these acid gases have resulted in high interest in the research and development of technologies to remove or convert these acid gases. The main challenge for the development of these technologies is to develop catalysts that are highly efficient, stable, and cost-effective, and many catalysts have been reported in this regard. CeO2 and CeO2-based catalysts have gained prominence in the removal and conversion of CO2, SO2, and NOx because of their structural robustness and redox and acid–basemore » properties. In this article, we provide a brief overview of the application of CeO2 and CeO2-based catalysts for the removal of CO2, SO2, and NOx gases with an emphasis on the fundamental understanding of the interactions of these acid gases with CeO2. The studies summarized in this review range from surface science using single crystals and thin films with precise crystallographic planes to practical catalysis applications of nanocrystalline and polycrystalline CeO2 materials with defects and dopants. After an introduction to the properties of CeO2 surfaces, their catalytic properties for conversions of different acid gases are reviewed and discussed. Lastly, we find that the surface atomic structure, oxygen vacancies, and surface acid–base properties of CeO2 play vital roles in the surface chemistry and structure evolution during the interactions of acid gases with CeO2 and CeO2-based catalysts.« less

  20. Effect of B-site isovalent doping on electrical and ferroelectric properties of lead free bismuth titanate ceramics

    NASA Astrophysics Data System (ADS)

    Subohi, Oroosa; Kumar, G. S.; Malik, M. M.; Kurchania, Rajnish

    2016-06-01

    In the present work, zirconium modified bismuth titanate ceramics have been studied as potential lead-free ferroelectric materials over a broad temperature range (RT - 800 °C). Polycrystalline samples of Bi4Ti3-xZrxO12 (x=0.2, 0.4, 0.6) (BZrT) with high electrical resistivity were prepared using the solution combustion technique. The effect of Zr doping on the crystalline structure, ferroelectric properties and electrical conduction characteristics of BZrT ceramics were explored. Addition of zirconium to bismuth titanate enhances its dielectric constant and reduces the loss factor as it introduces orthorhombic distortion in bismuth titanate lattice which is exhibited by the growth along (00_10) lattice plane. Activation energy due to relaxation is found to be greater than that due to conduction thus confirming that electrical conduction in these ceramics is not due to relaxation of dipoles. Remanent polarization of the doped samples increases as the Zirconium content increases.

  1. Multi-susceptibile Single-Phased Ceramics with Both Considerable Magnetic and Dielectric Properties by Selectively Doping

    NASA Astrophysics Data System (ADS)

    Liu, Chuyang; Zhang, Yujing; Jia, Jingguo; Sui, Qiang; Ma, Ning; Du, Piyi

    2015-04-01

    Multiferroic ceramics with extraordinary susceptibilities coexisting are vitally important for the multi-functionality and integration of electronic devices. However, multiferroic composites, as the most potential candidates, will introduce inevitable interface deficiencies and thus dielectric loss from dissimilar phases. In this study, single-phased ferrite ceramics with considerable magnetic and dielectric performances appearing simultaneously were fabricated by doping target ions in higher valence than that of Fe3+, such as Ti4+, Nb5+ and Zr4+, into BaFe12O19. In terms of charge balance, Fe3+/Fe2+ pair dipoles are produced through the substitution of Fe3+ by high-valenced ions. The electron hopping between Fe3+ and Fe2+ ions results in colossal permittivity. Whilst the single-phased ceramics doped by target ions exhibit low dielectric loss naturally due to the diminishment of interfacial polarization and still maintain typical magnetic properties. This study provides a convenient method to attain practicable materials with both outstanding magnetic and dielectric properties, which may be of interest to integration and multi-functionality of electronic devices.

  2. Luminescent properties of Eu{sup 2+}-doped BaGdF{sub 5} glass ceramics a potential blue phosphor for ultra-violet light-emitting diode

    SciTech Connect

    Zhang, Weihuan; Zhang, Yuepin Ouyang, Shaoye; Zhang, Zhixiong; Wang, Qian; Xia, Haiping

    2015-01-14

    Eu{sup 2+} doped transparent oxyfluoride glass ceramics containing BaGdF{sub 5} nanocrystals were successfully fabricated by melt-quenching technique under a reductive atmosphere. The structure of the glass and glass ceramics were investigated by differential scanning calorimetry, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The luminescent properties were investigated by transmission, excitation, and emission spectra. The decay time of the Gd{sup 3+} ions at 312 nm excited with 275 nm were also investigated. The results of XRD and TEM indicated the existence of BaGdF5 nanocrystals in the transparent glass ceramics. The excitation spectra of Eu{sup 2+} doped glass ceramics showed an excellent overlap with the main emission region of an ultraviolet light-emitting diode (UV-LED). Compared with the as-made glass, the emission of glass ceramics is much stronger by a factor of increasing energy transfer efficiency from Gd{sup 3+} to Eu{sup 2+} ions, the energy transfer efficiency from Gd{sup 3+} to Eu{sup 2+} ions was discussed. In addition, the chromaticity coordinates of glass and glass ceramics specimens were also discussed, which indicated that the Eu{sup 2+} doped BaGdF{sub 5} glass ceramics may be used as a potential blue-emitting phosphor for UV-LED.

  3. High Performance Ceramic Interconnect Material for Solid Oxide Fuel Cells (SOFCs): Ca- and Transition Metal-doped Yttrium Chromite

    SciTech Connect

    Yoon, Kyung J.; Stevenson, Jeffry W.; Marina, Olga A.

    2011-10-15

    The effect of transition metal substitution on thermal and electrical properties of Ca-doped yttrium chromite was investigated in relation to use as a ceramic interconnect in high temperature solid oxide fuel cells (SOFCs). 10 at% Co, 4 at% Ni, and 1 at% Cu substitution on B-site of 20 at% Ca-doped yttrium chromite led to a close match of thermal expansion coefficient (TEC) with that of 8 mol% yttria-stabilized zirconia (YSZ), and a single phase Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 remained stable between 25 and 1100 degree C over a wide oxygen partial pressure range. Doping with Cu significantly facilitated densification of yttrium chromite. Ni dopant improved both electrical conductivity and dimensional stability in reducing environments, likely through diminishing the oxygen vacancy formation. Substitution with Co substantially enhanced electrical conductivity in oxidizing atmosphere, which was attributed to an increase in charge carrier density and hopping mobility. Electrical conductivity of Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 at 900 degree C is 57 S/cm in air and 11 S/cm in fuel (pO2=5×10^-17 atm) environments. Chemical compatibility of doped yttrium chromite with other cell components was verified at the processing temperatures. Based on the chemical and dimensional stability, sinterability, and thermal and electrical properties, Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 is suggested as a promising SOFC ceramic interconnect to potentially overcome technical limitations of conventional acceptor-doped lanthanum chromites.

  4. High performance ceramic interconnect material for solid oxide fuel cells (SOFCs): Ca- and transition metal-doped yttrium chromite

    NASA Astrophysics Data System (ADS)

    Yoon, Kyung Joong; Stevenson, Jeffrey W.; Marina, Olga A.

    2011-10-01

    The effect of transition metal substitution on thermal and electrical properties of Ca-doped yttrium chromite was investigated in relation to use as a ceramic interconnect in high temperature solid oxide fuel cells (SOFCs). 10 at.% Co, 4 at.% Ni, and 1 at.% Cu substitution on B-site of 20 at.% Ca-doped yttrium chromite led to a close match of thermal expansion coefficient (TEC) with that of 8 mol% yttria-stabilized zirconia (YSZ), and a single phase Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 remained stable between 25 and 1100 °C over a wide oxygen partial pressure range. Doping with Cu significantly facilitated densification of yttrium chromite. Ni dopant improved both electrical conductivity and dimensional stability in reducing environments, likely through diminishing the oxygen vacancy formation. Substitution with Co substantially enhanced electrical conductivity in oxidizing atmosphere, which was attributed to an increase in charge carrier density and hopping mobility. Electrical conductivity of Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 at 900 °C is 57 S cm-1 in air and 11 S cm-1 in fuel (pO2 = 5 × 10-17 atm) environments. Chemical compatibility of doped yttrium chromite with other cell components was verified at the processing temperatures. Based on the chemical and dimensional stability, sinterability, and thermal and electrical properties, Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 is suggested as a promising SOFC ceramic interconnect to potentially overcome technical limitations of conventional acceptor-doped lanthanum chromites.

  5. Microstructure and Dielectric Properties of Yttrium-Doped BaSn0.05Ti0.95O3 Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Yuanliang; Cui, Zhimin; Sang, Rongli; Li, Zhongqiu; Ma, Xuegang; Su, Hao

    2016-06-01

    The microstructure and dielectric properties of Y3+-doped BaSn0.05Ti0.95O3 (BTS5) ceramics were investigated. All BTS5 ceramics possess a single phase with a perovskite structure, and the Rietveld analysis further shows that the material exhibits tetragonal structure with space group P4mm. The amount of Y2O3 can greatly affect the dielectric properties of BTS5. The Curie peak of the blank sample is the highest, and the Curie peak of the samples is obviously suppressed after the doping of Y3+, and the dielectric maximum decreased up to 0.05 mol.% of Y3+ doping and then increased beyond 0.05 mol.% of Y2O3. Due to the amount of doping of Y3+ ions, the lattice distortion is decreased with the increase of Y3+ concentration, which decreases the short-range harmonic restoring force, so T c shifts to a higher temperature in Y3+ doped BTS ceramics. In addition, the dielectric losses of 0.05-0.6 mol.% Y3+-doped BTS5 ceramics are very stable with the increasing environmental temperature, making them superior candidates for applications.

  6. Microstructure and Dielectric Properties of Yttrium-Doped BaSn0.05Ti0.95O3 Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Yuanliang; Cui, Zhimin; Sang, Rongli; Li, Zhongqiu; Ma, Xuegang; Su, Hao

    2016-10-01

    The microstructure and dielectric properties of Y3+-doped BaSn0.05Ti0.95O3 (BTS5) ceramics were investigated. All BTS5 ceramics possess a single phase with a perovskite structure, and the Rietveld analysis further shows that the material exhibits tetragonal structure with space group P4 mm. The amount of Y2O3 can greatly affect the dielectric properties of BTS5. The Curie peak of the blank sample is the highest, and the Curie peak of the samples is obviously suppressed after the doping of Y3+, and the dielectric maximum decreased up to 0.05 mol.% of Y3+ doping and then increased beyond 0.05 mol.% of Y2O3. Due to the amount of doping of Y3+ ions, the lattice distortion is decreased with the increase of Y3+ concentration, which decreases the short-range harmonic restoring force, so T c shifts to a higher temperature in Y3+ doped BTS ceramics. In addition, the dielectric losses of 0.05-0.6 mol.% Y3+-doped BTS5 ceramics are very stable with the increasing environmental temperature, making them superior candidates for applications.

  7. The evolution mechanism of defect dipoles and high strain in MnO2-doped KNN lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Zhao, Zhihao; Dai, Yejing; Li, Xiaolei; Zhao, Zhe; Zhang, Xiaowen

    2016-04-01

    Defect dipoles in acceptor-doped (K0.5Na0.5)NbO3-based ceramics have a significant influence on their electrical properties. The present study examined the influence of the sintering atmosphere on the electrical properties of MnO2-doped (K0.5Na0.5)NbO3. The poled and aged samples sintered in the Ar atmosphere depicted unusual behavior related to the formation of defect dipoles ( M n2+ N b ‴ - VO .. ) ' , aligned in the poling direction having larger polarity. The S-E loop of the poled and aged MnO2-doped (K0.5Na0.5)NbO3 ceramics sintered in the Ar atmosphere revealed larger strains in the poling direction and restrained strains in the opposite direction. Furthermore, it is observed that the unipolar electro-strain could reach 0.28% (d33* = 800 pm/V) at 3.5 kV/mm, a value nearly 5.6-fold higher than those obtained in the air atmosphere (0.05%). This method based on the sintering atmosphere and process control provides a promising way to obtain substantial electro-strain values suitable for applications in high-displacement actuators.

  8. Synthesis of novel CeO2-BiVO4/FAC composites with enhanced visible-light photocatalytic properties.

    PubMed

    Zhang, Jin; Wang, Bing; Li, Chuang; Cui, Hao; Zhai, Jianping; Li, Qin

    2014-09-01

    To utilize visible light more effectively in photocatalytic reactions, a fly ash cenosphere (FAC)-supported CeO2-BiVO4 (CeO2-BiVO4/FAC) composite photocatalyst was prepared by modified metalorganic decomposition and impregnation methods. The physical and photophysical properties of the composite have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and UV-Visible diffuse reflectance spectra. The XRD patterns exhibited characteristic diffraction peaks of both BiVO4 and CeO2 crystalline phases. The XPS results showed that Ce was present as both Ce(4+) and Ce(3+) oxidation states in CeO2 and dispersed on the surface of BiVO4 to constitute a p-n heterojunction composite. The absorption threshold of the CeO2-BiVO4/FAC composite shifted to a longer wavelength in the UV-Vis absorption spectrum compared to the pure CeO2 and pure BiVO4. The composites exhibited enhanced photocatalytic activity for Methylene Blue (MB) degradation under visible light irradiation. It was found that the 7.5wt.% CeO2-BiVO4/FAC composite showed the highest photocatalytic activity for MB dye wastewater treatment.

  9. Morphology-dependent interplay of reduction behaviors, oxygen vacancies and hydroxyl reactivity of CeO2 nanocrystals.

    PubMed

    Gao, Yuxian; Li, Rongtan; Chen, Shilong; Luo, Liangfeng; Cao, Tian; Huang, Weixin

    2015-12-21

    Reduction behaviors, oxygen vacancies and hydroxyl groups play decisive roles in the surface chemistry and catalysis of oxides. Employing isothermal H2 reduction we simultaneously reduced CeO2 nanocrystals with different morphologies, created oxygen vacancies and produced hydroxyl groups. The morphology of CeO2 nanocrystals was observed to strongly affect the reduction process and the resultant oxygen vacancy structure. The resultant oxygen vacancies are mainly located on the surfaces of CeO2 cubes and rods but in the subsurface/bulk of CeO2 octahedra. The reactivity of isolated bridging hydroxyl groups on CeO2 nanocrystals was found to depend on the local oxygen vacancy concentration, in which they reacted to produce water at low local oxygen vacancy concentrations but to produce both water and hydrogen with increasing local oxygen vacancy concentration. These results reveal a morphology-dependent interplay among the reduction behaviors, oxygen vacancies and hydroxyl reactivity of CeO2 nanocrystals, which deepens the fundamental understanding of the surface chemistry and catalysis of CeO2.

  10. Effects of CeO2 nanoparticles on system performance and bacterial community dynamics in a sequencing batch reactor.

    PubMed

    Qiu, Guanglei; Neo, Sin-Yi; Ting, Yen-Peng

    2016-01-01

    The effects of CeO2 nanoparticles (NPs) on the system performance and the bacterial community dynamics in a sequencing batch reactor (SBR) were investigated, along with the fate and removal of CeO2 NPs within the SBR. Significant impact was observed on nitrification; NH4+-N removal efficiency decreased from almost 100% to around 70% after 6 days of continuous exposure to 1.0 mg/L of CeO2 NPs, followed by a gradual recovery until a stable value of around 90% after 20 days. Additionally, CeO2 NPs also led to a significant increase in the protein content in the soluble microbial products, showing the disruptive effects of CeO2 NPs on the extracellular polymeric substance matrix and related activated sludge structure. Denaturing gradient gel electrophoresis analysis showed remarkable changes in the bacterial community structure in the activated sludge after exposure to CeO2 NPs. CeO2 NPs were effectively removed in the SBR mainly via sorption onto the sludge. However, the removal efficiency decreased from 95 to 80% over 30 days. Mass balance evaluation showed that up to 50% of the NPs were accumulated within the activated sludge and were removed with the waste sludge.

  11. Effects of CeO2 nanoparticles on system performance and bacterial community dynamics in a sequencing batch reactor.

    PubMed

    Qiu, Guanglei; Neo, Sin-Yi; Ting, Yen-Peng

    2016-01-01

    The effects of CeO2 nanoparticles (NPs) on the system performance and the bacterial community dynamics in a sequencing batch reactor (SBR) were investigated, along with the fate and removal of CeO2 NPs within the SBR. Significant impact was observed on nitrification; NH4+-N removal efficiency decreased from almost 100% to around 70% after 6 days of continuous exposure to 1.0 mg/L of CeO2 NPs, followed by a gradual recovery until a stable value of around 90% after 20 days. Additionally, CeO2 NPs also led to a significant increase in the protein content in the soluble microbial products, showing the disruptive effects of CeO2 NPs on the extracellular polymeric substance matrix and related activated sludge structure. Denaturing gradient gel electrophoresis analysis showed remarkable changes in the bacterial community structure in the activated sludge after exposure to CeO2 NPs. CeO2 NPs were effectively removed in the SBR mainly via sorption onto the sludge. However, the removal efficiency decreased from 95 to 80% over 30 days. Mass balance evaluation showed that up to 50% of the NPs were accumulated within the activated sludge and were removed with the waste sludge. PMID:26744939

  12. Designed synthesis of multi-functional PEGylated Yb2O3:Gd@SiO2@CeO2 islands core@shell nanostructure.

    PubMed

    Li, Junqi; Yao, Shuang; Song, Shuyan; Wang, Xiao; Wang, Yinghui; Ding, Xing; Wang, Fan; Zhang, Hongjie

    2016-07-28

    Nanomaterials that can restrain or reduce the production of excessive reactive oxygen species such as H2O2 to defend and treat against Alzheimer's disease (AD) have attracted much attention. In this paper, we adopt the strategy of layer-by-layer deposition; namely, first synthesizing available gadolinium-doped ytterbia nanoparticles (Yb2O3:Gd NPs) as cores, and then coating them with silica via the classical Stöber method to prevent leakage and act as a carrier for subsequent ceria deposition and PEGylation, and finally obtain the expected core@shell-structured nanocomposite of PEGylated Yb2O3:Gd@SiO2@CeO2 islands. The nanomaterial has proved not only to be a high-performance dual-modal contrast agent for use in MRI and CT, but also to exhibit excellent catalase mimetic activity, which may help the prognosis, diagnosis and treatment of AD in the future. In addition, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy characterization have revealed the successful design and synthesis of the cores with remarkable size uniformity, with well-distributed CeO2 islands decorated on the surface of SiO2 shells, and tightly immobilized PEG. PMID:27351951

  13. X-ray absorption fine structure of aged, Pu-doped glass and ceramic waste forms

    NASA Astrophysics Data System (ADS)

    Hess, N. J.; Weber, W. J.; Conradson, S. D.

    1998-04-01

    X-ray absorption spectroscopic (XAS) studies were performed on three compositionally identical, Pu-doped, borosilicate glasses prepared 15 years ago at different α-activities by varying the 239Pu/ 238Pu isotopic ratio. The resulting α-activities ranged from 1.9×10 7 to 4.2×10 9 Bq/g and have current, accumulated doses between 8.8×10 15 to 1.9×10 18 α-decays/g. Two ceramic, polycrystalline zircon (ZrSiO 4) samples prepared 16 years ago with 10.0 wt% Pu was also investigated. Varying the 239Pu/ 238Pu isotopic ratio in these samples resulted in α-activities of 2.5×10 8 and 5.6×10 10 Bq/g and current, accumulated doses of 1.2×10 17 and 2.8×10 19 α-decays/g. The multicomponent composition of the waste forms permitted XAS investigations at six absorption edges for the borosilicate glass and at three absorption edges for the polycrystalline zircons. For both waste forms, analysis of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectra indicates that the local environment around the cations exhibits different degrees of disorder as a result of the accumulated α-decay dose. In general, cations with short cation-oxygen bonds show little effect from self-radiation whereas cations with long cation-oxygen bonds show a greater degree of disorder with accumulated α-decay dose.

  14. Modified giant dielectric properties of samarium doped CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

    SciTech Connect

    Thongbai, Prasit; Putasaeng, Bundit; Yamwong, Teerapon; Maensiri, Santi

    2012-09-15

    Highlights: ► Grain size of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics was greatly decreased by doping with Sm{sup 3+}. ► ε′ and tan δ decreased with increasing the concentration of Sm{sup 3+} doping. ► Ca{sub 0.925}Sm{sub 0.05}Cu{sub 3}Ti{sub 4}O{sub 12} exhibited ε′ ∼ 10,863 and low tan δ ∼ 0.043 at 20 °C and 1 kHz. -- Abstract: Effects of Sm{sup 3+} substitution on the microstructure and dielectric properties of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics were investigated. The grain size of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics was greatly decreased by doping with Sm{sup 3+}, resulting from the ability of Sm{sup 3+} to inhibit the grain growth rate. This result can cause a decrease in the dielectric constant (ε′) and loss tangent (tan δ) of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics. Interestingly, high dielectric permittivity (ε′ ∼ 10,863) and low loss tangent (tan δ ∼ 0.043 at 20 °C and 1 kHz) were observed in the Ca{sub 0.925}Sm{sub 0.05}Cu{sub 3}Ti{sub 4}O{sub 12} ceramic. Nonlinear electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics were modified by doping with Sm{sup 3+}. The dielectric relaxation behavior of Sm-doped CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics can be well ascribed based on the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.

  15. Erosion-Corrosion Property of CeO2-Modified HVOF WC-Co Coating

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Hang, Zongqiu; Chen, Hui; Ceng, Shengbo; Gou, Guoqing; Wang, Xiaomin; Tu, Mingjing; Wu, Xiangyang

    2016-04-01

    Rare-earth elements have been widely used in materials manufacturing to improve hardness and toughness. In this work, conventional, nanostructured, and CeO2-modified WC-12Co powders were sprayed using high-velocity oxygen flame spraying. The erosion-corrosion behavior and interaction of erosion and corrosion of the coatings in 3.5 wt.% NaCl solution were investigated. In situ observation was employed to analyze the failure mechanism. The results showed that the CeO2-modified WC-12Co coating possessed the best erosion-corrosion resistance, while the lowest corrosion resistance was exhibited by the conventional WC-12Co coating. The results also suggested that the erosion-corrosion mechanism in the three coatings was dominated by corrosion-accelerated erosion. However, the extent of acceleration of erosion by corrosion differed.

  16. Long-term aging of a CeO(2) based nanocomposite used for wood protection.

    PubMed

    Auffan, Melanie; Masion, Armand; Labille, Jerome; Diot, Marie-Ange; Liu, Wei; Olivi, Luca; Proux, Olivier; Ziarelli, Fabio; Chaurand, Perrine; Geantet, Christophe; Bottero, Jean-Yves; Rose, Jerome

    2014-05-01

    A multi-scale methodology was used to characterize the long-term behavior and chemical stability of a CeO2-based nanocomposite used as UV filter in wood stains. ATR-FTIR and (13)C NMR demonstrated that the citrate coated chelates with Ce(IV) through its central carboxyl- and its α-hydroxyl- groups at the surface of the unaged nanocomposite. After 42 days under artificial daylight, the citrate completely disappeared and small amount of degradation products remained attached to the surface even after 112 days. Moreover, the release/desorption of the citrate layer led to a surface reorganization of the nano-sized CeO2 core observed by XANES (Ce L3-edge). Such a surface and structural transformation of the commercialized nanocomposite could have implications in term of fate, transport, and potential impacts towards the environment.

  17. Reactivity and reaction intermediates for acetic acid adsorbed on CeO2(111)

    DOE PAGESBeta

    Calaza, Florencia C.; Chen, Tsung -Liang; Mullins, David R.; Xu, Ye; Steven H. Overbury

    2015-05-02

    Adsorption and reaction of acetic acid on a CeO2(1 1 1) surface was studied by a combination of ultra-highvacuum based methods including temperature desorption spectroscopy (TPD), soft X-ray photoelectronspectroscopy (sXPS), near edge X-ray absorption spectroscopy (NEXAFS) and reflection absorption IRspectroscopy (RAIRS), together with density functional theory (DFT) calculations. TPD shows that thedesorption products are strongly dependent upon the initial oxidation state of the CeO2 surface, includingselectivity between acetone and acetaldehyde products. The combination of sXPS and NEXAFS demon-strate that acetate forms upon adsorption at low temperature and is stable to above 500 K, above whichpoint ketene, acetone and acetic acidmore » desorb. Furthermore, DFT and RAIRS show that below 500 K, bridge bondedacetate coexists with a moiety formed by adsorption of an acetate at an oxygen vacancy, formed bywater desorption.« less

  18. Stable Electron Field Emission from CeO2 Nanowires by Hydrothermal Method

    NASA Astrophysics Data System (ADS)

    Fu, Xing-Qiu; Feng, Ping; Wang, Chong; Wang, Tai-Hong

    2007-08-01

    CeO2 nanowires are successful synthesized by hydrothermal method and their field emission (FE) properties are investigated. The turn-on electric field is 5.8 V/μm at an emitter-anode spacing of 700 μm. The FE current is stable and the current fluctuations are less than 3% over 5 h. All the plotted Fowler-Nordheim curves yield straight lines, which are in agreement with the Fowler-Nordheim theory. The relationship between the field enhancement factor β and the emitter-anode spacing d follows a universal equation. Our results imply that the CeO2 nanowires are promising materials for fabricating FE cathodes.

  19. Mn3O4-CeO2 nano-catalysts: Synthesis, characterization and application

    NASA Astrophysics Data System (ADS)

    Anushree, Sharma, C.; Kumar, S.

    2016-05-01

    Nano-sized Mn3O4-CeO2 catalysts were synthesized by a cost effective co-precipitation method, and were studied as a heterogeneous catalyst for wet air oxidation of paper industry wastewater at mild operating conditions of 90 °C and 1 atm. The structural, micro-structural and textural properties of synthesized catalysts were studied through various characterization techniques, i.e. XRD, TEM, N2-sorption and EDS. The catalytic activity of Mn3O4-CeO2 was interestingly found to be higher than the corresponding single-metal oxides, and the Ce50Mn50 nano-catalyst with small crystallite size (4.5 nm), high specific surface area (75 m2g-1) and high porosity (0.24 ccg-1) was found to be most efficient with 69% color, 60% COD, 59% TOC, 48% AOX removal.

  20. Structural and compositional characterization of laser ablated CeO 2 thin films

    NASA Astrophysics Data System (ADS)

    Sánchez, F.; Varela, M.; Ferrater, C.; García-Cuenca, M. V.; Aguiar, R.; Morenza, J. L.

    1993-06-01

    CeO 2 thin films have been deposited on Si(100) substrates by laser ablation in ultrahigh vacuum. The structural and compositional properties of the films were studied by XRD, TEM, XPS and SIMS. All the films deposited in the temperature range 400-850°C have a preferential orientation ( hhh). The deposition in an oxygen environment (10 -4 mbar) results in a great reduction of the film crystallinity. The existance of a 5 nm thick amorphous layer between the CeO 2 film and the Si(100) substrate has been observed by TEM. XPS and SIMS results seem to indicate that this layer is a cerium silicade. SIMS profiles show that Ce diffuses toward the substrate, whereas O and Si do not diffuse.

  1. YBCO thin films on CeO2 buffered silver substrates

    NASA Astrophysics Data System (ADS)

    Gallistl, B.; Gritzner, G.

    2008-02-01

    CeO2 was deposited on silver substrates by the chemical solution deposition method. Silver was dipped into a 0.05 M Ce(NO3)3 solution, dried in air and then annealed in air at 900 °C for 30 minutes. The CeO2 buffer layer was characterized by X-ray diffraction and scanning electron microscopy. YBCO was deposited onto the buffered substrate via screen printing. The YBCO films where sintered at temperatures of 880 °C and 890 °C. Dense and crack free YBCO layers were obtained with transition temperatures (Tc0) up to 83 K. Characterization of the superconducting film was performed by X-ray diffraction and SEM.

  2. Three-photon near-infrared quantum cutting in Tm{sup 3+}-doped transparent oxyfluoride glass ceramics

    SciTech Connect

    Yu, D. C.; Zhang, J. P.; Chen, Q. J.; Zhang, W. J.; Yang, Z. M.; Zhang, Q. Y.

    2012-10-22

    Efficient three-step sequential three-photon near-infrared (NIR) quantum cutting in Tm{sup 3+}-doped transparent oxyfluoride glass ceramics has been demonstrated, where an absorbed blue photon could be cut into three NIR photons at 1190, 1460, and 1800 nm with quantum yield greater than unity. On the basis of static and dynamic photoemission, monitored excitation, and time-resolved fluorescence spectra, we investigate in detail the underlying optoelectronic mechanism. Further development of an efficient triply-cutting material might open up a path towards ultra-efficient photonic devices, which enables more photons emitted than absorbed in the excitation process.

  3. Cell uptake, intracellular distribution, fate and reactive oxygen species generation of polymer brush engineered CeO2-x NPs

    NASA Astrophysics Data System (ADS)

    Qiu, Yuan; Rojas, Elena; Murray, Richard A.; Irigoyen, Joseba; Gregurec, Danijela; Castro-Hartmann, Pablo; Fledderman, Jana; Estrela-Lopis, Irina; Donath, Edwin; Moya, Sergio E.

    2015-04-01

    Cerium Oxide nanoparticles (CeO2-x NPs) are modified with polymer brushes of negatively charged poly (3-sulfopropylmethacrylate) (PSPM) and positively charged poly (2-(methacryloyloxy)ethyl-trimethylammonium chloride) (PMETAC) by Atom Transfer Radical Polymerisation (ATRP). CeO2-x NPs are fluorescently labelled by covalently attaching Alexa Fluor® 488/Fluorescein isothiocyanate to the NP surface prior to polymerisation. Cell uptake, intracellular distribution and the impact on the generation of intracellular Reactive Oxygen Species (ROS) with respect to CeO2-x NPs are studied by means of Raman Confocal Microscopy (CRM), Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). PSPM and PMETAC coated CeO2-x NPs show slower and less uptake compared to uncoated Brush modified NPs display a higher degree of co-localisation with cell endosomes and lysosomes after 24 h of incubation. They also show higher co-localisation with lipid bodies when compared to unmodified CeO2-x NPs. The brush coating does not prevent CeO2-x NPs from displaying antioxidant properties.Cerium Oxide nanoparticles (CeO2-x NPs) are modified with polymer brushes of negatively charged poly (3-sulfopropylmethacrylate) (PSPM) and positively charged poly (2-(methacryloyloxy)ethyl-trimethylammonium chloride) (PMETAC) by Atom Transfer Radical Polymerisation (ATRP). CeO2-x NPs are fluorescently labelled by covalently attaching Alexa Fluor® 488/Fluorescein isothiocyanate to the NP surface prior to polymerisation. Cell uptake, intracellular distribution and the impact on the generation of intracellular Reactive Oxygen Species (ROS) with respect to CeO2-x NPs are studied by means of Raman Confocal Microscopy (CRM), Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). PSPM and PMETAC coated CeO2-x NPs show slower and less uptake compared to uncoated Brush modified NPs display a higher degree of co-localisation with cell endosomes and lysosomes after 24 h of incubation. They also show higher co-localisation with lipid bodies when compared to unmodified CeO2-x NPs. The brush coating does not prevent CeO2-x NPs from displaying antioxidant properties. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00884k

  4. Investigation of oxygen vacancies in CeO2/Pt system with synchrotron light techniques

    NASA Astrophysics Data System (ADS)

    Braglia, L.; Bugaev, A. L.; Lomachenko, K. A.; Soldatov, A. V.; Lamberti, C.; Guda, A. A.

    2016-05-01

    A peculiar property of ceria is the ease to form oxygen vacancies, producing reactive sites or facilitating ionic diffusion. For these reasons ceria promotes catalytic activities for a number of important reactions when it is used as a support for transition metals. In our work we study the temporal evolution of oxygen vacancies formation by time-resolved XANES at Ce K- edge and XRD measurements on CeO2/Pt nanoparticles, successfully monitoring the reaction of CO oxidation.

  5. CO Oxidation mechanism on CeO2-supported Au nanoclusters

    SciTech Connect

    Kim H. Y.; Henkelman, G.

    2013-09-08

    To reveal the richer chemistry of CO oxidation by CeO2 supported Au Nanoclusters(NCs)/Nanoparticles, we design Au13 and Au12 supported on a flat and a stepped-CeO2 model (Au/CeO2) and study various kinds of CO oxidation mechanisms at the Au-CeO2 interface and the Au NC as well.

  6. Development of Nano-crystalline Doped-Ceramic Enabled Fiber Sensors for High Temperature In-Situ Monitoring of Fossil Fuel Gases

    SciTech Connect

    Xiao, Hai; Dong, Junhang; Lin, Jerry; Romero, Van

    2012-03-01

    This is a final technical report for the first project year from July 1, 2005 to Jan 31, 2012 for DoE/NETL funded project DE-FC26-05NT42439: Development of Nanocrystalline Doped-Ceramic Enabled Fiber Sensors for High Temperature In-Situ Monitoring of Fossil Fuel Gases. This report summarizes the technical progresses and achievements towards the development of novel nanocrystalline doped ceramic material-enabled optical fiber sensors for in situ and real time monitoring the gas composition of flue or hot gas streams involved in fossil-fuel based power generation and hydrogen production.

  7. WO 3/CeO 2/YSZ nanocomposite as a potential catalyst for methanol reforming

    NASA Astrophysics Data System (ADS)

    Natile, Marta Maria; Glisenti, Antonella

    A WO 3/CeO 2/YSZ nanocomposite material [W/Zr nominal atomic ratio = 0.025, Ce/Zr nominal atomic ratio = 0.020] was prepared by wet impregnation and characterized by means of X-ray photoelectron and diffuse reflectance infrared Fourier transform spectroscopic techniques, X-ray diffraction and thermal analysis. Both tungsten and cerium oxides are significantly reduced at the interface with YSZ: Ce(III), in particular, seems to be the prevailing species. The interaction of the WO 3/CeO 2/YSZ nanopowder with pyridine and CO 2 allowed to investigate the acidic/basic sites. Weak contributions at 1602, 1625 and 1647 cm -1 suggest the presence of Lewis and Brønsted acidic sites, whereas basic sites are not evidenced by the interaction with carbon dioxide. The presence of tungsten oxide causes the decrement of the acidic/basic sites, as indicated by the comparison with the results obtained on the CeO 2/YSZ support. Consistently, the interaction with methanol is mainly molecular. The oxidation of methanol was investigated both in the absence and in the presence of water. In the last case carbon dioxide starts forming from room temperature.

  8. Exposure to CeO(2) nanoparticles during flame spray process.

    PubMed

    Leppänen, Maija; Lyyränen, Jussi; Järvelä, Merja; Auvinen, Ari; Jokiniemi, Jorma; Pimenoff, Joe; Tuomi, Timo

    2012-09-01

    The use of nanotechnology in different fields is increasing rapidly. Engineered nanoparticles (ENPs) may have adverse effect on human health, but little is known about the exposure levels of ENPs at occupational settings. In this study, exposure levels of cerium oxide (CeO(2)) ENPs were measured during enclosed flame spray process used for coating and surface modification of materials. Particle number concentration, mass concentration, and morphology and composition of the ENPs were studied. The average particle number concentration varied from 4.7·10(3) to 2.1·10(5) 1/cm(3) inside the enclosure, and from 4.6·10(3) to 1.4·10(4) 1/cm(3) outside the enclosure. The average mass concentrations inside and outside the enclosure were 320 and 66 μg/m(3), respectively. A batch-type process caused significant variation in the concentrations, especially inside the enclosure. CeO(2) ENPs were mainly chainlike aggregates, consisting of spherical 20-40 nm primary particles having crystalline structure. In conclusion, enclosure of the process with efficient ventilation seemed to be an effective means to reduce the exposure to CeO(2) ENPs as expected. PMID:21770722

  9. [Catalytic degradation of naphthalene by CuO (-CeO2)/Al2O3].

    PubMed

    Zha, Jian; Zhou, Hong-Cang; He, Du-Liang; Shan, Long; Zhang, Lu; Xie, Jie

    2014-10-01

    Three catalysts CuO/Al2O3, CeO2/Al2O3 and CuO-CeO2/Al2O3 were prepared by the impregnation method. The textural and structural properties of the synthesized catalysts were characterized by N2 adsorption/desorption, SEM and XRD, and the effect of active ingredients, flow rate and reaction temperature on catalytic degradation of naphthalene (NaP) were investigated in fixed-bed reactor. The experimental results show that the prepared 18% CeO2/Al2O3 has a low catalytic activity of NaP. Nevertheless, both 18% CuO/Al2O3 and 9% CuO-9% CeO2/Al2O3 exhibit high catalytic activity whose removal efficiencies at 300°C can reach 91% and 89%, respectively. Besides, compared with CuO/Al2O3, CuO-CeO2/Al2O3 possesses a higher low-temperature activity. Furthermore, the variation of flow rates has little effect on the performance of two catalysts.

  10. [Catalytic degradation of naphthalene by CuO (-CeO2)/Al2O3].

    PubMed

    Zha, Jian; Zhou, Hong-Cang; He, Du-Liang; Shan, Long; Zhang, Lu; Xie, Jie

    2014-10-01

    Three catalysts CuO/Al2O3, CeO2/Al2O3 and CuO-CeO2/Al2O3 were prepared by the impregnation method. The textural and structural properties of the synthesized catalysts were characterized by N2 adsorption/desorption, SEM and XRD, and the effect of active ingredients, flow rate and reaction temperature on catalytic degradation of naphthalene (NaP) were investigated in fixed-bed reactor. The experimental results show that the prepared 18% CeO2/Al2O3 has a low catalytic activity of NaP. Nevertheless, both 18% CuO/Al2O3 and 9% CuO-9% CeO2/Al2O3 exhibit high catalytic activity whose removal efficiencies at 300°C can reach 91% and 89%, respectively. Besides, compared with CuO/Al2O3, CuO-CeO2/Al2O3 possesses a higher low-temperature activity. Furthermore, the variation of flow rates has little effect on the performance of two catalysts. PMID:25693411

  11. Dielectric and electrical studies of Pr{sup 3+} doped nano CaSiO{sub 3} perovskite ceramics

    SciTech Connect

    Kulkarni, Sandhya; Nagabhushana, B.M.; Parvatikar, Narsimha; Koppalkar, Anilkumar; Shivakumara, C.; Damle, R.

    2014-02-01

    Highlights: • CaSiO{sub 3}:Pr{sup 3+} was prepared by facile low temperature solution combustion method. • The crystalline phase of the product is obtained by adopting sintering method. • Samples prepared at 500 °C and calcined at 900 °C for 3 h showed β-phase. • The Pr{sup 3+} doped CaSiO{sub 3} shows “unusual results”. • The electrical microstructure has been accepted to be of internal barrier layer capacitor. - Abstract: CaSiO{sub 3} nano-ceramic powder doped with Pr{sup 3+} has been prepared by solution combustion method. The powder Ca{sub 0.95}Pr{sub 0.05}SiO{sub 3} is investigated for its dielectric and electrical properties at room temperature to study the effect of doping. The sample is characterized by X-ray diffraction and infrared spectroscopy. The size of either of volume elements of CaSiO{sub 3}:Pr{sup 3+} estimated from transmission electron microscopy is about 180–200 nm. The sample shows colossal dielectric response at room temperature. This colossal dielectric behaviour follows Debye-type relaxation and can be explained by Maxwell–Wagner (MW) polarization. However, analysis of impedance and electric modulus data using Cole–Cole plot shows that it deviates from ideal Debye behaviour resulting from the distribution of relaxation times. The distribution in the relaxation times may be attributed to existence of electrically heterogeneous grains, insulating grain boundary, and electrode contact regions. Doping, thus, results in substantial modifications in the dielectric and electrical properties of the nano-ceramic CaSiO{sub 3}.

  12. Temperature dependent emission and absorption cross section of Yb3+ doped yttrium lanthanum oxide (YLO) ceramic and its application in diode pumped amplifier.

    PubMed

    Banerjee, Saumyabrata; Koerner, Joerg; Siebold, Mathias; Yang, Qiuhong; Ertel, Klaus; Mason, Paul D; Phillips, P Jonathan; Loeser, Markus; Zhang, Haojia; Lu, Shenzhou; Hein, Joachim; Schramm, Ulrich; Kaluza, Malte C; Collier, John L

    2013-07-01

    Temperature dependent absorption and emission cross-sections of 5 at% Yb(3+) doped yttrium lanthanum oxide (Yb:YLO) ceramic between 80K and 300 K are presented. In addition, we report on the first demonstration of ns pulse amplification in Yb:YLO ceramic. A pulse energy of 102 mJ was extracted from a multi-pass amplifier setup. The amplification bandwidth at room temperature confirms the potential of Yb:YLO ceramic for broad bandwidth amplification at cryogenic temperatures.

  13. Influence of Zr{sup 4+} doping on structural and electrical properties of SrBi{sub 4}Ti{sub 4}O{sub 15} ceramic

    SciTech Connect

    Nayak, P. Panigrahi, S.; Badapanda, T.

    2015-06-24

    This article reports a systematic study of doping effects on the structural and electrical properties of layer structured strontium bismuth titanate ceramic. In this study monophasic SrBi{sub 4}Ti{sub 4-x}Zr{sub x}O{sub 15} with x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25 ceramics were synthesized from the solid-state reaction route. X-ray diffraction analysis shows that the Zr-modified SBT ceramics have a pure four-layer Aurivillius phase structure. Dielectric properties revealed that the diffuseness of phase transition increases where as corresponding permittivity value decrease with increasing Zr content. Piezoelectric properties of SBTZ ceramics were improved by the modification of Zirconium ion. Moreover, the reason behind for improvement of piezoelectric properties of modified SBTZ ceramics was also discussed.

  14. Enhancement of photocatalytic activity of combustion-synthesized CeO2/C3N4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Li, Dong-Feng; Yang, Ke; Wang, Xiao-qin; Ma, Ya-Li; Huang, Gui-Fang; Huang, Wei-Qing

    2015-09-01

    Nanocrystalline CeO2/C3N4 was synthesized via a one-step solution combustion method using urea as fuel for the first time. The effects of the molar ratio of urea to cerium chloride on the photocatalytic activity of the synthesized samples were investigated. The synthesized nanocrystalline CeO2/C3N4 shows small size and large surface exposure area. Photocatalytic degradation of methylene blue demonstrates that the synthesized nanocrystalline CeO2/C3N4 possesses enhanced photocatalytic activity. It is proposed that the enhanced photocatalytic activity might be related to the favorable morphology and structure, and the effective charge separation between C3N4 and CeO2 in the photocatalytic process.

  15. A facile method of fabricating mechanical durable anti-icing coatings based on CeO2 microparticles

    NASA Astrophysics Data System (ADS)

    Wang, Pengren; Peng, Chaoyi; Wu, Binrui; Yuan, Zhiqing; Yang, Fubiao; Zeng, Jingcheng

    2015-07-01

    Compromising between hydrophobicity and mechanical durability may be a feasible approach to fabricating usable anti-icing coatings. This work improves the contact angle of current commercial anti-icing coatings applied to wind turbine blades dramatically and keeps relatively high mechanical durability. CeO2 microparticles and diluent were mixed with fluorocarbon resin to fabricate high hydrophobic coatings on the glass fiber reinforced epoxy composite substrates. The proportion of CeO2 microparticles and diluent influences the contact angles significantly. The optimum mass ratio of fluorocarbon resin to CeO2 microparticles to diluent is 1:1.5:1, which leads to the highest contact angle close to 140°. The microscopy analysis shows that the CeO2 microparticles form nano/microscale hierarchical structure on the surface of the coatings.

  16. Grain-boundary phases in hot-pressed silicon nitride containing Y2O3 and CeO2 additives

    NASA Technical Reports Server (NTRS)

    Guha, J. P.; Hench, L. L.

    1983-01-01

    Auger electron spectroscopy in conjunction with X-ray powder diffraction and scanning electron microscopy is used to analyze the grain-boundary phases of Y2O3- and CeO2-doped Si3N4 hot-pressed materials in order to demonstrate that the additives concentrate predominantly in the grain boundaries of Si3N4 in the form of various oxynitride phases. A high oxygen content observed in sample fracture surfaces was found to be consistent with the existence of an oxygen-enriched phase in the grain boundaries. The presence of yttrium and cerium in the fracture surfaces and an overall increase in the O/N ratio imply that the additive oxides are predominantly concentrated in the intergranular phases.

  17. Photocatalytic activity of the binary composite CeO2/SiO2 for degradation of dye

    NASA Astrophysics Data System (ADS)

    Phanichphant, Sukon; Nakaruk, Auppatham; Channei, Duangdao

    2016-11-01

    In this study, CeO2 photocatalyst was modified by composite with SiO2 to increase efficiency and improve photocatalytic activity. The as-prepared SiO2 particles have been incorporated into the precursor mixture of CeO2 by homogeneous precipitation and subsequent calcination process. The phase compositions of CeO2 before and after compositing with SiO2 were identified by X-ray diffraction (XRD). The morphology and particle size of CeO2/SiO2 composite was analyzed by high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). The results showed SiO2 spheres with the particle size approximately 100-120 nm, and a uniform layer of CeO2 nanoparticles with a diameter of about 5-7 nm that were fully composite to the surfaces of SiO2. The X-ray photoelectron spectroscopy (XPS) technique was carried out in order to characterize the change in valence state and composite characteristic by shifted peaks of binding energies. The photocatalytic activity was studied through the degradation of Rhodamine B in aqueous solution under visible light exposure. The highest photocatalytic efficiency of CeO2/SiO2 composite was also obtained. To explain the high photocatalytic efficiency of CeO2/SiO2 composite, the proposed mechanism involves the high surface properties of the CeO2/SiO2 composite, as measured by Brunauer-Emmett-Teller (BET) method.

  18. Microstructural evolution of CeO2 from porous structures to clusters of nanosheet arrays assisted by gas bubbles via electrodeposition.

    PubMed

    Li, Gao-Ren; Qu, Dun-Lin; Yu, Xiao-Lan; Tong, Ye-Xiang

    2008-04-15

    Here we report the preparation of porous CeO2 and clusters of CeO2 nanosheet arrays via a simple, efficient electrochemical approach. Gas bubbles functioning as a dynamic template were utilized in our research for the synthesis of nanosheet array clusters. The Hc and Mr values of porous CeO2 are almost the same as those of CeO2 nanosheet array clusters at 5 K, and they are about 5916 Oe and 8.83 x 10(-4) emu, respectively. However, the saturation magnetization of CeO2 nanosheet array clusters is much larger than that of porous CeO2 structures. The magnetic property of the prepared CeO2 deposits may be caused by the existence of Ce(III), indicating potential interest in the nanodevices because of their electronic and magnetic properties.

  19. CeO2 nanoparticles induce no changes in phenanthrene toxicity to the soil organisms Porcellionides pruinosus and Folsomia candida.

    PubMed

    Tourinho, Paula S; Waalewijn-Kool, Pauline L; Zantkuijl, Irene; Jurkschat, Kerstin; Svendsen, Claus; Soares, Amadeu M V M; Loureiro, Susana; van Gestel, Cornelis A M

    2015-03-01

    Cerium oxide nanoparticles (CeO2 NPs) are used as diesel fuel additives to catalyze oxidation. Phenanthrene is a major component of diesel exhaust particles and one of the most common pollutants in the environment. This study aimed at determining the effect of CeO2 NPs on the toxicity of phenanthrene in Lufa 2.2 standard soil for the isopod Porcellionides pruinosus and the springtail Folsomia candida. Toxicity tests were performed in the presence of CeO2 concentrations of 10, 100 or 1000mg Ce/kg dry soil and compared with results in the absence of CeO2 NPs. CeO2 NPs had no adverse effects on isopod survival and growth or springtail survival and reproduction. For the isopods, LC50s for the effect of phenanthrene ranged from 110 to 143mg/kg dry soil, and EC50s from 17.6 to 31.6mg/kg dry soil. For the springtails, LC50s ranged between 61.5 and 88.3mg/kg dry soil and EC50s from 52.2 to 76.7mg/kg dry soil. From this study it may be concluded that CeO2 NPs have a low toxicity and do not affect toxicity of phenanthrene to isopods and springtails. PMID:25499053

  20. MnO2/CeO2 for catalytic ultrasonic decolorization of methyl orange: Process parameters and mechanisms.

    PubMed

    Zhao, He; Zhang, Guangming; Chong, Shan; Zhang, Nan; Liu, Yucai

    2015-11-01

    MnO2/CeO2 catalyst was prepared and characterized by means of Brunauer-Emmet-Teller (BET) method, X-ray diffraction (XRD) and scanning electron microscope (SEM). The characterization showed that MnO2/CeO2 had big specific surface area and MnO2 was dispersed homogeneously on the surface of CeO2. Excellent degradation efficiency of methyl orange was achieved by MnO2/CeO2 catalytic ultrasonic process. Operating parameters were studied and optimized. The optimal conditions were 10 min of ultrasonic irradiation, 1.0 g/L of catalyst dose, 2.6 of pH value and 1.3 W/ml of ultrasonic density. Under the optimal conditions, nearly 90% of methyl orange was removed. The mechanism of methyl orange degradation was further studied. The decolorization mechanism in the ultrasound-MnO2/CeO2 system was quite different with that in the ultrasound-MnO2 system. Effects of manganese and cerium in catalytic ultrasonic process were clarified. Manganese ions in solution contributed to generating hydroxyl free radical. MnO2/CeO2 catalyst strengthened the oxidation ability of ultrasound and realized complete decolorization of methyl orange.

  1. Synthesis and Characterization of CeO2 Nanoparticles via Solution Combustion Method for Photocatalytic and Antibacterial Activity Studies.

    PubMed

    Ravishankar, Thammadihalli Nanjundaiah; Ramakrishnappa, Thippeswamy; Nagaraju, Ganganagappa; Rajanaika, Hanumanaika

    2015-04-01

    CeO2 nanoparticles have been proven to be competent photocatalysts for environmental applications because of their strong redox ability, nontoxicity, long-term stability, and low cost. We have synthesized CeO2 nanoparticles via solution combustion method using ceric ammonium nitrate as an oxidizer and ethylenediaminetetraacetic acid (EDTA) as fuel at 450 °C. These nanoparticles exhibit good photocatalytic degradation and antibacterial activity. The obtained product was characterized by various techniques. X-ray diffraction data confirms a cerianite structure: a cubic phase CeO2 having crystallite size of 35 nm. The infrared spectrum shows a strong band below 700 cm(-1) due to the Ce-O-Ce stretching vibrations. The UV/Vis spectrum shows maximum absorption at 302 nm. The photoluminescence spectrum shows characteristic peaks of CeO2 nanoparticles. Scanning electron microscopy (SEM) images clearly show the presence of a porous network with a lot of voids. From transmission electron microscopy (TEM) images, it is clear that the particles are almost spherical, and the average size of the nanoparticles is found to be 42 nm. CeO2 nanoparticles exhibit photocatalytic activity against trypan blue at pH 10 in UV light, and the reaction follows pseudo first-order kinetics. Finally, CeO2 nanoparticles also reduce Cr(VI) to Cr(III) and show antibacterial activity against Pseudomonas aeruginosa.

  2. CeO2 nanoparticles induce no changes in phenanthrene toxicity to the soil organisms Porcellionides pruinosus and Folsomia candida.

    PubMed

    Tourinho, Paula S; Waalewijn-Kool, Pauline L; Zantkuijl, Irene; Jurkschat, Kerstin; Svendsen, Claus; Soares, Amadeu M V M; Loureiro, Susana; van Gestel, Cornelis A M

    2015-03-01

    Cerium oxide nanoparticles (CeO2 NPs) are used as diesel fuel additives to catalyze oxidation. Phenanthrene is a major component of diesel exhaust particles and one of the most common pollutants in the environment. This study aimed at determining the effect of CeO2 NPs on the toxicity of phenanthrene in Lufa 2.2 standard soil for the isopod Porcellionides pruinosus and the springtail Folsomia candida. Toxicity tests were performed in the presence of CeO2 concentrations of 10, 100 or 1000mg Ce/kg dry soil and compared with results in the absence of CeO2 NPs. CeO2 NPs had no adverse effects on isopod survival and growth or springtail survival and reproduction. For the isopods, LC50s for the effect of phenanthrene ranged from 110 to 143mg/kg dry soil, and EC50s from 17.6 to 31.6mg/kg dry soil. For the springtails, LC50s ranged between 61.5 and 88.3mg/kg dry soil and EC50s from 52.2 to 76.7mg/kg dry soil. From this study it may be concluded that CeO2 NPs have a low toxicity and do not affect toxicity of phenanthrene to isopods and springtails.

  3. Synthesis and Characterization of CeO2 Nanoparticles via Solution Combustion Method for Photocatalytic and Antibacterial Activity Studies

    PubMed Central

    Ravishankar, Thammadihalli Nanjundaiah; Ramakrishnappa, Thippeswamy; Nagaraju, Ganganagappa; Rajanaika, Hanumanaika

    2015-01-01

    CeO2 nanoparticles have been proven to be competent photocatalysts for environmental applications because of their strong redox ability, nontoxicity, long-term stability, and low cost. We have synthesized CeO2 nanoparticles via solution combustion method using ceric ammonium nitrate as an oxidizer and ethylenediaminetetraacetic acid (EDTA) as fuel at 450 °C. These nanoparticles exhibit good photocatalytic degradation and antibacterial activity. The obtained product was characterized by various techniques. X-ray diffraction data confirms a cerianite structure: a cubic phase CeO2 having crystallite size of 35 nm. The infrared spectrum shows a strong band below 700 cm−1 due to the Ce−O−Ce stretching vibrations. The UV/Vis spectrum shows maximum absorption at 302 nm. The photoluminescence spectrum shows characteristic peaks of CeO2 nanoparticles. Scanning electron microscopy (SEM) images clearly show the presence of a porous network with a lot of voids. From transmission electron microscopy (TEM) images, it is clear that the particles are almost spherical, and the average size of the nanoparticles is found to be 42 nm. CeO2 nanoparticles exhibit photocatalytic activity against trypan blue at pH 10 in UV light, and the reaction follows pseudo first-order kinetics. Finally, CeO2 nanoparticles also reduce CrVI to CrIII and show antibacterial activity against Pseudomonas aeruginosa. PMID:25969812

  4. Mild activation of CeO2-supported gold nanoclusters and insight into the catalytic behavior in CO oxidation.

    PubMed

    Li, Weili; Ge, Qingjie; Ma, Xiangang; Chen, Yuxiang; Zhu, Manzhou; Xu, Hengyong; Jin, Rongchao

    2016-01-28

    We report a new activation method and insight into the catalytic behavior of a CeO2-supported, atomically precise Au144(SR)60 nanocluster catalyst (where thiolate -SR = -SCH2CH2Ph) for CO oxidation. An important finding is that the activation of the catalyst is closely related to the production of active oxygen species on CeO2, rather than ligand removal of the Au144(SR)60 clusters. A mild O2 pretreatment (at 80 °C) can activate the catalyst, and the addition of reductive gases (CO or H2) can enhance the activation effects of O2 pretreatment via a redox cycle in which CO could reduce the surface of CeO2 to produce oxygen vacancies-which then adsorb and activate O2 to produce more active oxygen species. The CO/O2 pulse experiments confirm that CO is adsorbed on the cluster catalyst even with ligands on, and active oxygen species present on the surface of the pretreated catalyst reacts with CO pulses to generate CO2. The Au144(SR)60/CeO2 exhibits high CO oxidation activity at 80 °C without the removal of thiolate ligands. The surface lattice-oxygen of the support CeO2 possibly participates in the oxidation of CO over the Au144(SR)60/CeO2 catalyst.

  5. Mild activation of CeO2-supported gold nanoclusters and insight into the catalytic behavior in CO oxidation.

    PubMed

    Li, Weili; Ge, Qingjie; Ma, Xiangang; Chen, Yuxiang; Zhu, Manzhou; Xu, Hengyong; Jin, Rongchao

    2016-01-28

    We report a new activation method and insight into the catalytic behavior of a CeO2-supported, atomically precise Au144(SR)60 nanocluster catalyst (where thiolate -SR = -SCH2CH2Ph) for CO oxidation. An important finding is that the activation of the catalyst is closely related to the production of active oxygen species on CeO2, rather than ligand removal of the Au144(SR)60 clusters. A mild O2 pretreatment (at 80 °C) can activate the catalyst, and the addition of reductive gases (CO or H2) can enhance the activation effects of O2 pretreatment via a redox cycle in which CO could reduce the surface of CeO2 to produce oxygen vacancies-which then adsorb and activate O2 to produce more active oxygen species. The CO/O2 pulse experiments confirm that CO is adsorbed on the cluster catalyst even with ligands on, and active oxygen species present on the surface of the pretreated catalyst reacts with CO pulses to generate CO2. The Au144(SR)60/CeO2 exhibits high CO oxidation activity at 80 °C without the removal of thiolate ligands. The surface lattice-oxygen of the support CeO2 possibly participates in the oxidation of CO over the Au144(SR)60/CeO2 catalyst. PMID:26750474

  6. O/W/O double emulsion-assisted synthesis and catalytic properties of CeO 2 hollow microspheres

    NASA Astrophysics Data System (ADS)

    Zhang, DongEn; Xie, Qing; Wang, MingYan; Zhang, XiaoBo; Li, ShanZhong; Han, GuiQuan; Ying, AiLing; Chen, AiMei; Gong, JunYan; Tong, ZhiWei

    2010-09-01

    CeO 2 hollow microspheres have been fabricated through a simple thermal decomposition of precursor approach. The precursor with an average size of 10 μm was prepared in a reverse microemulsions containing Ce(NO 3) 3·6H 2O and CO(NH 2) 2 at 160 °C. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), selected area electron diffraction (SAED) and scanning electron microscopy (SEM). The possible formation mechanism of hollow spheres was discussed. In addition, the CeO 2 hollow microspheres modified glassy carbon electrode exhibit excellent sensing performance towards methyl orange, which provide a new application of CeO 2 hollow spheres. The catalytic activity of CeO 2 hollow spheres on the thermal decomposition of ammonium perchlorate (AP) also was investigated by TGA. The catalytic performance of CeO 2 hollow spheres is superior to that of commercial CeO 2 powder.

  7. Fate and Phytotoxicity of CeO2 Nanoparticles on Lettuce Cultured in the Potting Soil Environment

    PubMed Central

    Gui, Xin; Zhang, Zhiyong; Liu, Shutong; Ma, Yuhui; Zhang, Peng; He, Xiao; Li, Yuanyuan; Zhang, Jing; Li, Huafen; Rui, Yukui; Liu, Liming; Cao, Weidong

    2015-01-01

    Cerium oxide nanoparticles (CeO2 NPs) have been shown to have significant interactions in plants. Previous study reported the specific-species phytotoxicity of CeO2 NPs by lettuce (Lactuca sativa), but their physiological impacts and vivo biotransformation are not yet well understood, especially in relative realistic environment. Butterhead lettuce were germinated and grown in potting soil for 30 days cultivation with treatments of 0, 50, 100, 1000 mg CeO2 NPs per kg soil. Results showed that lettuce in 100 mg·kg-1 treated groups grew significantly faster than others, but significantly increased nitrate content. The lower concentrations treatment had no impact on plant growth, compared with the control. However, the higher concentration treatment significantly deterred plant growth and biomass production. The stress response of lettuce plants, such as Superoxide dismutase (SOD), Peroxidase (POD), Malondialdehyde(MDA) activity was disrupted by 1000 mg·kg-1 CeO2 NPs treatment. In addition, the presence of Ce (III) in the roots of butterhead lettuce explained the reason of CeO2 NPs phytotoxicity. These findings demonstrate CeO2 NPs modification of nutritional quality, antioxidant defense system, the possible transfer into the food chain and biotransformation in vivo. PMID:26317617

  8. Cell uptake, intracellular distribution, fate and reactive oxygen species generation of polymer brush engineered CeO(2-x) NPs.

    PubMed

    Qiu, Yuan; Rojas, Elena; Murray, Richard A; Irigoyen, Joseba; Gregurec, Danijela; Castro-Hartmann, Pablo; Fledderman, Jana; Estrela-Lopis, Irina; Donath, Edwin; Moya, Sergio E

    2015-04-21

    Cerium Oxide nanoparticles (CeO(2-x) NPs) are modified with polymer brushes of negatively charged poly (3-sulfopropylmethacrylate) (PSPM) and positively charged poly (2-(methacryloyloxy)ethyl-trimethylammonium chloride) (PMETAC) by Atom Transfer Radical Polymerisation (ATRP). CeO(2-x) NPs are fluorescently labelled by covalently attaching Alexa Fluor® 488/Fluorescein isothiocyanate to the NP surface prior to polymerisation. Cell uptake, intracellular distribution and the impact on the generation of intracellular Reactive Oxygen Species (ROS) with respect to CeO(2-x) NPs are studied by means of Raman Confocal Microscopy (CRM), Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). PSPM and PMETAC coated CeO(2-x) NPs show slower and less uptake compared to uncoated Brush modified NPs display a higher degree of co-localisation with cell endosomes and lysosomes after 24 h of incubation. They also show higher co-localisation with lipid bodies when compared to unmodified CeO(2-x) NPs. The brush coating does not prevent CeO(2-x) NPs from displaying antioxidant properties.

  9. Fate and Phytotoxicity of CeO2 Nanoparticles on Lettuce Cultured in the Potting Soil Environment.

    PubMed

    Gui, Xin; Zhang, Zhiyong; Liu, Shutong; Ma, Yuhui; Zhang, Peng; He, Xiao; Li, Yuanyuan; Zhang, Jing; Li, Huafen; Rui, Yukui; Liu, Liming; Cao, Weidong

    2015-01-01

    Cerium oxide nanoparticles (CeO2 NPs) have been shown to have significant interactions in plants. Previous study reported the specific-species phytotoxicity of CeO2 NPs by lettuce (Lactuca sativa), but their physiological impacts and vivo biotransformation are not yet well understood, especially in relative realistic environment. Butterhead lettuce were germinated and grown in potting soil for 30 days cultivation with treatments of 0, 50, 100, 1000 mg CeO2 NPs per kg soil. Results showed that lettuce in 100 mg·kg-1 treated groups grew significantly faster than others, but significantly increased nitrate content. The lower concentrations treatment had no impact on plant growth, compared with the control. However, the higher concentration treatment significantly deterred plant growth and biomass production. The stress response of lettuce plants, such as Superoxide dismutase (SOD), Peroxidase (POD), Malondialdehyde(MDA) activity was disrupted by 1000 mg·kg-1 CeO2 NPs treatment. In addition, the presence of Ce (III) in the roots of butterhead lettuce explained the reason of CeO2 NPs phytotoxicity. These findings demonstrate CeO2 NPs modification of nutritional quality, antioxidant defense system, the possible transfer into the food chain and biotransformation in vivo.

  10. Densification behavior, doping profile and planar waveguide laser performance of the tape casting YAG/Nd:YAG/YAG ceramics

    NASA Astrophysics Data System (ADS)

    Ge, Lin; Li, Jiang; Qu, Haiyun; Wang, Juntao; Liu, Jiao; Dai, Jiawei; Zhou, Zhiwei; Liu, Binglong; Kou, Huamin; Shi, Yun; Wang, Zheng; Pan, Yubai; Gao, Qingsong; Guo, Jingkun

    2016-10-01

    The sintering behavior and doping concentration profile of the planar waveguide YAG/Nd:YAG/YAG ceramics by the tape casting and solid-state reaction method were investigated on the basis of densification trajectory, microstructure evolution, and Nd3+ ions diffusion. The porosity of the green body by tape casting and cold isostatic pressing is about 38.6%. And the green bodies were consolidated from 1100 °C to 1800 °C for 0.5-20 h to study the densification and the doping diffusion behaviors. At the temperature higher than 1500 °C, pure YAG phase is formed, followed by the densification and grain growth process. With the increase of temperature, two sintering stages occur, corresponding to remarkable densification and significant grain growth, respectively. The mechanism controlling densification at 1550 °C is grain boundary diffusion. The diffusion of Nd3+ ions is more sensitive to temperature than the sintering time, and the minimum temperature required for the obvious diffusion of Nd3+ ions is higher than 1700 °C. Finally, planar waveguide YAG/1.5 at.%Nd:YAG/YAG transparent ceramics with in-line transmittance of 84.8% at 1064 nm were obtained by vacuum-sintering at 1780 °C for 30 h. The fluorescence lifetime of 4F3/2 state of Nd3+ in the specimen is about 259 μs. The prepared ceramic waveguide was tested in a laser amplifier and the laser pulse was amplificated from 87 mJ to 238 mJ, with the pump energy of 680 mJ.

  11. The structure of Er3+-doped oxy-fluoride transparent glass-ceramics studied by Raman scattering

    NASA Astrophysics Data System (ADS)

    Tikhomirov, V. K.; Seddon, A. B.; Ferrari, M.; Montagna, M.; Santos, L. F.; Almeida, R. M.

    2003-11-01

    We show that the structure of transparent oxy-fluoride glass-ceramics formed by heat treatment of glasses of typical composition 32(SiO2):9(AlO1.5):31.5(CdF2):18.5(PbF2): 5.5(ZnF2):3.5(ErF3) mol% consists of ~ 12 nm diameter, Er3+-doped, β-PbF2 nano-crystals embedded in a silica-based glass network and connected to it via non-bridging O and F anions, or fluorine linkages such as Pb-F-Cd and Pb-F-Zn. It is proposed that the glass network structure is mostly chain-like and dominated by Si(O,F)4 tetrahedra with two bridging O and two non-bridging O and/or F atoms (Q2 units). SiO4 tetrahedra with zero and one bridging O (Q0 and Q1 units, respectively) are also present in the glass structure, in the approximate proportion Q0:Q1:Q2 = 1:1:3, a characteristic which appears to be of primary importance. The flexible, chain-like glass-network, with many broken bonds, results in easy accommodation of the Er3+-doped PbF2 nano-crystals, which are grown by heat-treatment of the precursor glass. The boson peak in the Raman spectrum of the precursor glass decreases in intensity upon ceramming and is partly converted to narrow crystalline peaks at lower frequency, consistent with the precipitation of PbF2 crystalline nano-particles. It is suggested that the boson peak involves localized vibrations of broken or stretched Pb-F bonds. The mean free path for these vibrations increases with ceramming, which involves partial crystallization of the glass network, resulting in a shift of the boson peak vibrations to lower-frequency crystalline peaks.

  12. Eu-doped ZnO-HfO2 hybrid nanocrystal-embedded low-loss glass-ceramic waveguides

    NASA Astrophysics Data System (ADS)

    Ghosh, Subhabrata; N, Shivakiran Bhaktha B.

    2016-03-01

    We report on the sol-gel fabrication, using a dip-coating technique, of low-loss Eu-doped 70SiO2 -(30-x) HfO2-xZnO (x = 2, 5, 7 and 10 mol%) ternary glass-ceramic planar waveguides. Transmission electron microscopy and grazing incident x-ray diffraction experiments confirm the controlled growth of hybrid nanocrystals with an average size of 3 nm-25 nm, composed of ZnO encapsulated by a thin layer of nanocrystalline HfO2, with an increase of ZnO concentration from x = 2 mol% to 10 mol% in the SiO2-HfO2 composite matrix. The effect of crystallization on the local environment of Eu ions, doped in the ZnO-HfO2 hybrid nanocrystal-embedded glass-ceramic matrix, is studied using photoluminescence spectra, wherein an intense mixed-valence state (divalent as well as trivalent) emission of Eu ions is observed. The existence of Eu2+ and Eu3+ in the SiO2-HfO2-ZnO ternary matrix is confirmed by x-ray photoelectron spectroscopy. Importantly, the Eu{}2+,3+-doped ternary waveguides exhibit low propagation losses (0.3 ± 0.2 dB cm-1 at 632.8 nm) and optical transparency in the visible region of the electromagnetic spectrum, which makes ZnO-HfO2 nanocrystal-embedded SiO2-HfO2-ZnO waveguides a viable candidate for the development of on-chip, active, integrated optical devices.

  13. Eu-doped ZnO-HfO2 hybrid nanocrystal-embedded low-loss glass-ceramic waveguides.

    PubMed

    Ghosh, Subhabrata; Bhaktha B N, Shivakiran

    2016-03-11

    We report on the sol-gel fabrication, using a dip-coating technique, of low-loss Eu-doped 70SiO2 -[Formula: see text] HfO2-xZnO (x = 2, 5, 7 and 10 mol%) ternary glass-ceramic planar waveguides. Transmission electron microscopy and grazing incident x-ray diffraction experiments confirm the controlled growth of hybrid nanocrystals with an average size of 3 nm-25 nm, composed of ZnO encapsulated by a thin layer of nanocrystalline HfO2, with an increase of ZnO concentration from x = 2 mol% to 10 mol%  in the SiO2-HfO2 composite matrix. The effect of crystallization on the local environment of Eu ions, doped in the ZnO-HfO2 hybrid nanocrystal-embedded glass-ceramic matrix, is studied using photoluminescence spectra, wherein an intense mixed-valence state (divalent as well as trivalent) emission of Eu ions is observed. The existence of Eu(2+) and Eu(3+) in the SiO2-HfO2-ZnO ternary matrix is confirmed by x-ray photoelectron spectroscopy. Importantly, the Eu[Formula: see text]-doped ternary waveguides exhibit low propagation losses (0.3 ± 0.2 dB cm(-1) at 632.8 nm) and optical transparency in the visible region of the electromagnetic spectrum, which makes ZnO-HfO2 nanocrystal-embedded SiO2-HfO2-ZnO waveguides a viable candidate for the development of on-chip, active, integrated optical devices.

  14. Luminescent, dielectric, and ferroelectric properties of Pr doped Bi{sub 7}Ti{sub 4}NbO{sub 21} multifunctional ceramics

    SciTech Connect

    Zou, Hua; Hui, Xinwei; Wang, Xusheng Li, Jun; Li, Yanxia; Yao, Xi; Peng, Dengfeng

    2013-12-14

    Pr doped Bi{sub 7}Ti{sub 4}NbO{sub 21} (BTN) multifunctional ceramics were prepared by a conventional sintering technique and their luminescent, dielectric, and ferroelectric properties were investigated. The X-ray diffraction data showed that the samples were single phase, and the scanning electron microscopy image indicated that the ceramics had flake-like grains with uniform thickness. The red emission was observed under the ultraviolet and blue light excitation at room temperature. The thermal quench of luminescence was measured and the result indicated that Pr doped BTN ceramics might be potentially applied in luminescent probes and temperature sensors. With the increasing Pr{sup 3+} content, the intensity of the photoluminescence increased initially and then decreased due to concentration quenching; The Curie temperature T{sub c} was slightly shifted to the lower temperature; the ferroelectric properties was almost unchanged by doping. As a new multifunctional material, the Pr doped BTN ceramics could be used for a wide range of application, such as integrated electro-optical devices.

  15. The origin of giant dielectric relaxation and electrical responses of grains and grain boundaries of W-doped CaCu3Ti4O12 ceramics

    NASA Astrophysics Data System (ADS)

    Thongbai, Prasit; Jumpatam, Jutapol; Putasaeng, Bundit; Yamwong, Teerapon; Maensiri, Santi

    2012-12-01

    The origin of giant dielectric relaxation behavior and related electrical properties of grains and grain boundaries (GBs) of W6+-doped CaCu3Ti4O12 ceramics were studied using admittance and impedance spectroscopy analyses based on the brick-work layer model. Substitution of 1.0 at. % W6+ caused a slight decrease in GB capacitance, leading to a small decrease in the low-frequency dielectric constant. Surprisingly, W6+ doping ions have remarkable effects on the macroscopic dielectric relaxation and electrical properties of grains. X-ray photoelectron spectroscopy analysis suggested that the large enhancements of grain resistance and conduction activation energy of grains for the W6+-doped CaCu3Ti4O12 ceramic are caused by reductions in concentrations of Cu3+ and Ti3+ ions. Considering variation of dielectric properties together with changes in electrical properties of the W6+-doped CaCu3Ti4O12 ceramic, correlation between giant dielectric properties and electrical responses of grains and GBs can be described well by the internal barrier layer capacitor model. This model can ascribe mechanisms related to giant dielectric response and relaxation behavior in CaCu3Ti4O12 ceramics.

  16. Fabrication and microstructure of cerium doped lutetium aluminum garnet (Ce:LuAG) transparent ceramics by solid-state reaction method

    SciTech Connect

    Li, Junlang; Xu, Jian; Shi, Ying; Qi, Hongfang; Xie, Jianjun; Lei, Fang

    2014-07-01

    Highlights: • We fabricate Ce doped lutetium aluminum garnet ceramics by solid-state method. • The raw materials include Lu{sub 2}O{sub 3} nanopowders synthesized by co-precipitation method. • The density of the transparent ceramics reach 99.7% of the theoretical value. • The optical transmittance of the bulk ceramic at 550 nm was 57.48%. • Some scattering centers decrease the optical characteristic of the ceramic. - Abstract: Polycrystalline Ce{sup 3+} doped lutetium aluminum garnet (Ce:LuAG) transparent ceramics fabricated by one step solid-state reaction method using synthetic nano-sized Lu{sub 2}O{sub 3}, commercial α-Al{sub 2}O{sub 3} and CeO{sub 2} powders were investigated in this paper. The green compacts shaped by the mixed powders were successfully densified into Ce:LuAG transparent ceramics after vacuum sintering at 1750 °C for 10 h. The in-line optical transmittance of the Ce:LuAG ceramic made by home-made Lu{sub 2}O{sub 3} powders could reach 57.48% at 550 nm, which was higher than that of the ceramic made by commercial Lu{sub 2}O{sub 3} powders (22.96%). The microstructure observation showed that light scattering centers caused by micro-pores, aluminum segregation and refraction index inhomogeneities induced the decrease of optical transparency of the Ce:LuAG ceramics, which should be removed and optimized in the future work.

  17. Effects of Copper Doping on Dielectric and A.C. Conductivity in Layered Sodium Tri-Titanate Ceramic

    NASA Astrophysics Data System (ADS)

    Shripal; Dwivedi, Shailja; Singh, Rakesh; Tandon, R. P.

    2013-09-01

    Electron paramagnetic resonance (EPR) spectra of 0.01, 0.1 and 1.0 molar percentage (mp) of CuO doped derivatives of layered Na2Ti3O7 ceramic have been reported. The results show that copper substitutes as Cu2+ at Ti4+ octahedral sites. From the dependence of loss tangent (tan δ) and the relative permittivity (ɛ‧) on temperature and frequency, it is concluded that all the derivatives are of polar nature. The relaxation peaks at lower temperatures have been attributed to the presence of different types of dipoles, whereas peaks in the higher temperature region indicate possible ferroelectric phase transition. The dependence of conductivity on temperature show that electron hopping (polaron) conduction exists in a wide span of temperature range. However, the associated interlayer ionic conduction exists in a small temperature range. Interlayer alkali ion hopping mechanism of conduction has been proposed toward higher temperatures. The conductivity versus frequency plots reveal that the polaron conduction plays a prominent role toward the lower temperature side that diminishes with the rise in temperature. The most probable relaxation times for 0.01 and 0.1 mp CuO doped derivatives are almost same but it records an increased value for 1.0 mp doped material. This again attributes to the possible change in the symmetry of copper environment.

  18. Defect Structure of Li-Doped BPO 4: A Nanostructured Ceramic Electrolyte for Li-Ion Batteries

    NASA Astrophysics Data System (ADS)

    Jak, M. J. G.; Kelder, E. M.; Schoonman, J.

    1999-01-01

    In this paper the defect chemistry of Li-doped BPO4(BPO4-xLi2O, 0≤x≤0.1) is studied. This nanostructured ceramic electrolyte is used in all-solid-state Li-ion batteries. By changing the Li-doping level the influence on the crystal structure is studied and related to t he properties of the material. X-ray diffraction, Fourier-transformed infra-red spectroscopy (FT-IR),31P,11B, and7Li magic-angle-spinning solid state nuclear magnetic resonance, neutron diffraction, and inductively coupled plasma optical-emission spectroscopy measurements are used in order to study the structure. The electrical properties are studied with AC-impedance spectroscopy (AC-IS). The experimental data show that the defect structure of Li-doped BPO4can be described with two defect models, Li″B+2Li·iand V‴B+3Li·i, suggesting that the ionic conductivity takes place via interstitial Li ions.

  19. Redox Pathways for HCOOH Decomposition over CeO2 Surfaces

    SciTech Connect

    Senanayake,S.; Mullins, D.

    2008-01-01

    The reaction of HCOOH, the simplest C-1 carboxylic acid, has been studied on oxidized (CeO2) and reduced cerium oxide (CeOX) thin films. HCOOH has been proposed as an important C1 precursor to the formation of CO2 and H2 in the water-gas-shift (WGS) reaction, in which ceria is also used as a stable support rich in oxygen. The HCOOH is observed to adsorb by way of a formate intermediate species (HCOO-) through the dissociation of the acidic H over both CeO2 (Ce4+) and CeOX (Ce4+/Ce3+) surfaces. On the fully oxidized CeO2 surface, this H species reacts with surface O and desorbs as H2O when the temperature is <300 K. In addition to water, temperature programmed desorption spectra indicate the evolution of CO2 and H2 between 350 and 400 K followed by CO desorption in two regimes at 450 and 525 K. On reduced ceria, only CO and H2 were produced between 450 and 600 K. The reaction of HCOOH with ceria therefore leads to both the reduction of the oxide, through the formation of H2O and CO2, and oxidation of the oxide, through decomposition to H2 and CO, depending on the initial state of the ceria. C K-edge near-edge X-ray absorption fine structure and soft X-ray photoelectron spectroscopy indicate that formate and -OH were the only surface intermediates.

  20. Structure, bonding, and catalytic activity of monodisperse, transition-metal-substituted CeO2 nanoparticles.

    PubMed

    Elias, Joseph S; Risch, Marcel; Giordano, Livia; Mansour, Azzam N; Shao-Horn, Yang

    2014-12-10

    We present a simple and generalizable synthetic route toward phase-pure, monodisperse transition-metal-substituted ceria nanoparticles (M0.1Ce0.9O2-x, M = Mn, Fe, Co, Ni, Cu). The solution-based pyrolysis of a series of heterobimetallic Schiff base complexes ensures a rigorous control of the size, morphology and composition of 3 nm M0.1Ce0.9O2-x crystallites for CO oxidation catalysis and other applications. X-ray absorption spectroscopy confirms the dispersion of aliovalent (M(3+) and M(2+)) transition metal ions into the ceria matrix without the formation of any bulk transition metal oxide phases, while steady-state CO oxidation catalysis reveals an order of magnitude increase in catalytic activity with copper substitution. Density functional calculations of model slabs of these compounds confirm the stabilization of M(3+) and M(2+) in the lattice of CeO2. These results highlight the role of the host CeO2 lattice in stabilizing high oxidation states of aliovalent transition metal dopants that ordinarily would be intractable, such as Cu(3+), as well as demonstrating a rational approach to catalyst design. The current work demonstrates, for the first time, a generalizable approach for the preparation of transition-metal-substituted CeO2 for a broad range of transition metals with unparalleled synthetic control and illustrates that Cu(3+) is implicated in the mechanism for CO oxidation on CuO-CeO2 catalysts. PMID:25406101

  1. Photoluminescence, enhanced ferroelectric, and dielectric properties of Pr{sup 3+}-doped SrBi{sub 2}Nb{sub 2}O{sub 9} multifunctional ceramics

    SciTech Connect

    Zou, Hua; Yu, Yao; Li, Jun; Cao, Qiufeng; Wang, Xusheng; Hou, Junwei

    2015-09-15

    Pr{sup 3+}-doped SrBi{sub 2}Nb{sub 2}O{sub 9} (SBN) multifunctional ceramics were synthesized by the conventional solid state method. The photoluminescence (PL) excitation and emission spectra, enhanced ferroelectric and dielectric properties were investigated. The X-ray diffraction (XRD) and FESEM analyses indicated that the samples were simple phase and uniform flake-structure. Under the 250–350 nm ultraviolet (UV) excitations, the red emission was obtained and the optimal emission intensity was investigated when Pr doping level was 0.005 mol. With the increasing of the Pr{sup 3+} ion contents, the ferroelectric properties were enhanced obviously. As a new multifunctional material, the Pr{sup 3+}-doped SBN ceramics could be used for a wide range of application, such as integrated electro-optical devices.

  2. Effects of rare earth ionic doping on microstructures and electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

    SciTech Connect

    Xue, Renzhong; Chen, Zhenping; Dai, Haiyang; Liu, Dewei; Li, Tao; Zhao, Gaoyang

    2015-06-15

    Graphical abstract: The dielectric constant decreases monotonically with reduced RE doping ion radius and is more frequency independent compared with that of pure CCTO sample. - Highlights: • The mean grain sizes decrease monotonically with reduced RE doping ionic radius. • Doping gives rise to the monotonic decrease of ϵ{sub r} with reduced RE ionic radius. • The nonlinear coefficient and breakdown field increase with RE ionic doping. • α of all the samples is associated with the potential barrier width rather than Φ{sub b}. - Abstract: Ca{sub 1–x}R{sub x}Cu{sub 3}Ti{sub 4}O{sub 12}(R = La, Nd, Eu, Gd, Er; x = 0 and 0.005) ceramics were prepared by the conventional solid-state method. The influences of rare earth (RE) ion doping on the microstructure, dielectric and electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) ceramics were investigated systematically. Single-phase formation is confirmed by XRD analyses. The mean grain size decreases monotonically with reduced RE ion radius. The EDS results reveal that RE ionic doping reduces Cu-rich phase segregation at the grain boundaries (GBs). Doping gives rise to the monotonic decrease of dielectric constant with reduced RE ionic radius but significantly improves stability with frequency. The lower dielectric loss of doped samples is obtained due to the increase of GB resistance. In addition, the nonlinear coefficient and breakdown field increase with RE ionic doping. Both the fine grains and the enhancement of potential barrier at GBs are responsible for the improvement of the nonlinear current–voltage properties in doped CCTO samples.

  3. Effect of Tourmaline-Doped on the Far Infrared Emission of Iron Ore Tailings Ceramics.

    PubMed

    Liu, Jie; Meng, Junping; Liang, Jinsheng; Zhang, Hongchen; Gu, Xiaoyang

    2016-04-01

    Iron ore tailings as secondary resources have been of great importance to many countries in the world. Their compositions are similar to that of infrared emission ceramics, but there are few reports about it. In addition, tourmaline has high infrared emission properties due to its unique structure. With the purpose of expanding functional utilization of iron ore tailings, as well as reducing the production cost of far infrared ceramics, a new kind of far infrared emission ceramics was prepared by using iron ore tailings, calcium carbonate, silica, and natural tourmaline. The ceramics powders were characterized by Fourier transform infrared spectroscope, X-ray diffraction and scanning electron microscopy, respectively. The results show that after being sintered at 1065 °C, the percentage of pseudobrookite and lattice strain of samples increased with increasing the elbaite content. Furthermore, the added tourmaline was conducive to the densification sintering of ceramics. The appearance of Li-O vibration at 734.73 cm-1, as well as the strengthened Fe-O vibration at 987.68 cm-1 were attributed to the formation of Li0.375Fe1.23Ti1.4O5 solid solution, which led the average far infrared emissivity of ceramics increase from 0.861 to 0.906 within 8-14 µm.

  4. Effect of Tourmaline-Doped on the Far Infrared Emission of Iron Ore Tailings Ceramics.

    PubMed

    Liu, Jie; Meng, Junping; Liang, Jinsheng; Zhang, Hongchen; Gu, Xiaoyang

    2016-04-01

    Iron ore tailings as secondary resources have been of great importance to many countries in the world. Their compositions are similar to that of infrared emission ceramics, but there are few reports about it. In addition, tourmaline has high infrared emission properties due to its unique structure. With the purpose of expanding functional utilization of iron ore tailings, as well as reducing the production cost of far infrared ceramics, a new kind of far infrared emission ceramics was prepared by using iron ore tailings, calcium carbonate, silica, and natural tourmaline. The ceramics powders were characterized by Fourier transform infrared spectroscope, X-ray diffraction and scanning electron microscopy, respectively. The results show that after being sintered at 1065 °C, the percentage of pseudobrookite and lattice strain of samples increased with increasing the elbaite content. Furthermore, the added tourmaline was conducive to the densification sintering of ceramics. The appearance of Li-O vibration at 734.73 cm-1, as well as the strengthened Fe-O vibration at 987.68 cm-1 were attributed to the formation of Li0.375Fe1.23Ti1.4O5 solid solution, which led the average far infrared emissivity of ceramics increase from 0.861 to 0.906 within 8-14 µm. PMID:27451708

  5. Role of Microstructure and Surface Defects on the Dissolution Kinetics of CeO2, a UO2 Fuel Analogue.

    PubMed

    Corkhill, Claire L; Bailey, Daniel J; Tocino, Florent Y; Stennett, Martin C; Miller, James A; Provis, John L; Travis, Karl P; Hyatt, Neil C

    2016-04-27

    The release of radionuclides from spent fuel in a geological disposal facility is controlled by the surface mediated dissolution of UO2 in groundwater. In this study we investigate the influence of reactive surface sites on the dissolution of a synthesized CeO2 analogue for UO2 fuel. Dissolution was performed on the following: CeO2 annealed at high temperature, which eliminated intrinsic surface defects (point defects and dislocations); CeO2-x annealed in inert and reducing atmospheres to induce oxygen vacancy defects and on crushed CeO2 particles of different size fractions. BET surface area measurements were used as an indicator of reactive surface site concentration. Cerium stoichiometry, determined using X-ray Photoelectron Spectroscopy (XPS) and supported by X-ray Diffraction (XRD) analysis, was used to determine oxygen vacancy concentration. Upon dissolution in nitric acid medium at 90 °C, a quantifiable relationship was established between the concentration of high energy surface sites and CeO2 dissolution rate; the greater the proportion of intrinsic defects and oxygen vacancies, the higher the dissolution rate. Dissolution of oxygen vacancy-containing CeO2-x gave rise to rates that were an order of magnitude greater than for CeO2 with fewer oxygen vacancies. While enhanced solubility of Ce(3+) influenced the dissolution, it was shown that replacement of vacancy sites by oxygen significantly affected the dissolution mechanism due to changes in the lattice volume and strain upon dissolution and concurrent grain boundary decohesion. These results highlight the significant influence of defect sites and grain boundaries on the dissolution kinetics of UO2 fuel analogues and reduce uncertainty in the long term performance of spent fuel in geological disposal.

  6. Stability of engineered nanomaterials in complex aqueous matrices: Settling behaviour of CeO2 nanoparticles in natural surface waters.

    PubMed

    Van Koetsem, Frederik; Verstraete, Simon; Van der Meeren, Paul; Du Laing, Gijs

    2015-10-01

    The stability of engineered nanoparticles (ENPs) in complex aqueous matrices is a key determinant of their fate and potential toxicity towards the aquatic environment and human health. Metal oxide nanoparticles, such as CeO2 ENPs, are increasingly being incorporated into a wide range of industrial and commercial applications, which will undoubtedly result in their (unintentional) release into the environment. Hereby, the behaviour and fate of CeO2 ENPs could potentially serve as model for other nanoparticles that possess similar characteristics. The present study examined the stability and settling of CeO2 ENPs (7.3±1.4 nm) as well as Ce(3+) ions in 10 distinct natural surface waters during 7d, under stagnant and isothermal experimental conditions. Natural water samples were collected throughout Flanders (Belgium) and were thoroughly characterized. For the majority of the surface waters, a substantial depletion (>95%) of the initially added CeO2 ENPs was observed just below the liquid surface of the water samples after 7d. In all cases, the reduction was considerably higher for CeO2 ENPs than for Ce(3+) ions (<68%). A first-order kinetics model was able to describe the observed time-dependant removal of both CeO2 ENPs (R(2)≥0.998) and Ce(3+) ions (R(2)≥0.812) from the water column, at least in case notable sedimentation occurred over time. Solution-pH appeared to be a prime parameter governing nanoparticle colloidal stability. Moreover, the suspended solids (TSS) content also seemed to be an important factor affecting the settling rate and residual fraction of CeO2 ENPs as well as Ce(3+) ions in natural surface waters. Correlation results also suggest potential association and co-precipitation of CeO2 ENPs with aluminium- and iron-containing natural colloidal material. The CeO2 ENPs remained stable in dispersion in surface water characterized by a low pH, ionic strength (IS), and TSS content, indicating the eventual stability and settling behaviour of the nanoparticles was likely determined by a combination of physicochemical parameters. Finally, ionic release from the nanoparticle surface was also examined and appeared to be negligible in all of the tested natural waters.

  7. Structural, morphological and optical properties of CeO2 thin films deposited by RF sputtering

    NASA Astrophysics Data System (ADS)

    Murugan, R.; Vijayaprasath, G.; Sakthivel, P.; Mahalingam, T.; Ravi, G.

    2016-05-01

    Cerium oxide (CeO2) thin films were deposited on glass substrates by sputtering at various substrate temperatures. CeO2 films were characterized by X-ray diffraction, FESEM, PL and Raman analyses. X-ray diffraction patterns of films reveal fcc cubic structure with preferential orientation along (2 2 0) crystallographic plane. SEM images show that the particles are uniformly distributed on the film surface. The films were found to be well adheared to the substrates and pin holes are not observed on the surface of the films. PL spectra exhibits a strong near band-gap-edge emission and a broad blue, green luminescence, which can be assigned to the presence of Ce and O vacancies, amorphous phases, deep level impurities and structural defects. The relative intensity between the different peaks of the bands related to defects or impurities was studied as a tool for quality control of the films. Moreover, vibrational measurements through Raman analysis were carried out and the results are discussed.

  8. Surface potentials of (111), (110) and (100) oriented CeO2-x thin films

    NASA Astrophysics Data System (ADS)

    Wardenga, Hans F.; Klein, Andreas

    2016-07-01

    Differently oriented CeO2 thin films were prepared by radio frequency magnetron sputter deposition from a nominally undoped CeO2 target. (111), (110) and (100) oriented films were achieved by deposition onto Al2O3(0001)/Pt(111), MgO(110)/Pt(110) and SrTiO3:Nb(100) substrates, respectively. Epitaxial growth is verified using X-ray diffraction analysis. The films were analyzed by in situ photoelectron spectroscopy to determine the ionization potential, work function, Fermi level position and Ce3+ concentration at the surface in dependence of crystal orientation, deposition conditions and post-deposition treatment in reducing and oxidizing atmosphere. We observed a very high variation of the work function and ionization potential of more than 2 eV for all surface orientations, while the Fermi level varies by only 0.3 eV within the energy gap. The work function generally decreases with increasing Ce3+ surface concentration but comparatively high Ce3+ concentrations remain even after strongly oxidizing treatments. This is related to the presence of subsurface oxygen vacancies.

  9. Theoretical Study of Trimethylacetic Acid Adsorption on CeO 2 (111) Surface

    DOE PAGESBeta

    Wang, Weina; Thevuthasan, S.; Wang, Wenliang; Yang, Ping

    2016-01-11

    We investigated trimethylacetic acid (TMAA) adsorption on stoichiometric and oxygen-deficient CeO2(111) surfaces using density functional theory that accounts for the on-site Coulomb interaction via a Hubbard term (DFT+U) and long-range dispersion correction. Both the molecular state and dissociative state (TMAA → TMA– + H+) were identified on stoichiometric and oxygen-deficient CeO2(111) surfaces. For the stoichiometric surface, two thermodynamically favorable configurations with adsorption energies of the order of -30 kcal/mol are identified; one is a molecule adsorption state, and the other one is a dissociative state. For the oxygen-deficient surface, dissociative states are more favorable than molecular states. Moreover, the mostmore » favorable configuration is the dissociative adsorption of TMAA with the adsorption energy of the order of -77 kcal/mol. The dissociated TMA moiety takes the position of oxygen vacancy, forming three Ce–O bonds. The signature vibrational frequencies for these thermodynamically stable structures are reported as well as their electronic structures. The effects of long-range dispersion interactions are found to be negligible for geometries but important for adsorption energies.« less

  10. Portable Enzyme-Paper Biosensors Based on Redox-Active CeO2 Nanoparticles.

    PubMed

    Karimi, A; Othman, A; Andreescu, S

    2016-01-01

    Portable, nanoparticle (NP)-enhanced enzyme sensors have emerged as powerful devices for qualitative and quantitative analysis of a variety of analytes for biomedicine, environmental applications, and pharmaceutical fields. This chapter describes a method for the fabrication of a portable, paper-based, inexpensive, robust enzyme biosensor for the detection of substrates of oxidase enzymes. The method utilizes redox-active NPs of cerium oxide (CeO2) as a sensing platform which produces color in response to H2O2 generated by the action of oxidase enzymes on their corresponding substrates. This avoids the use of peroxidases which are routinely used in conjunction with glucose oxidase. The CeO2 particles serve dual roles, as high surface area supports to anchor high loadings of the enzyme as well as a color generation reagent, and the particles are recycled multiple times for the reuse of the biosensor. These sensors are small, light, disposable, inexpensive, and they can be mass produced by standard, low-cost printing methods. All reagents needed for the analysis are embedded within the paper matrix, and sensors stored over extended periods of time without performance loss. This novel sensor is a general platform for the in-field detection of analytes that are substrates for oxidase enzymes in clinical, food, and environmental samples. PMID:27112400

  11. Optical and spectral studies on pure and europium doped olgite type Na(Sr,Ba)PO4 ceramics.

    PubMed

    Jawaher, K Rackesh; Jagannathan, R; Das, S Jerome; Krishnan, S

    2015-04-01

    Europium ion doped olgite type Na(Sr,Ba)PO4 ceramics, a new generation of light emitting bulb, was prepared by a high temperature solid-state reaction method. The synthesized materials were subjected to various characterizations such as X-ray powder diffraction, Scanning electron microscopy and FT-IR spectra measurements. The EPR spectrum of the sample exhibits a well-resolved hyperfine structure of 151Eu2+ and 153Eu2+ isotopes and the g value has been calculated. Fluorescence spectra revealed that europium ions were present in divalent as well as in the trivalent oxidation states. The critical distance for energy transfer between Eu2+ and Eu2+ ion is calculated as 20Å, which is in good agreement with that of experimental data. The FTIR analysis reveals all the vibrations of PO4(3-) ions.

  12. Measurement of quantum yield of up-conversion Luminescence in Er(3+)-doped nano-glass-ceramics.

    PubMed

    Rodríguez, V D; Tikhomirov, V K; Méndez-Ramos, J; del-Castillo, J; Görller-Walrand, C

    2009-03-01

    A measurement of quantum yield of up-conversion luminescence has been done for the Er(3+)-doped transparent oxyfluoride glass-ceramics 32(SiO,)9(AlO1.5)31.5(CdF2)18.5(PbF2)5.5(ZnF2): 3.5(ErF3) mol%, where most of Er3+ dopants partition in 8 nm diameter nano-crystals Er10Pb25F65. The yield was found by newly proposed method using the pump power dependence of the resonant luminescence. The result of the measurement points out that a theoretical maximum of 50% may be reached for the up-conversion luminescence yield in this material. This high yield is shown to be due to low phonon energy and short inter-dopant distances in the nano-crystals.

  13. Waveguides in Ni-doped glass and glass-ceramic written with a 1 kHz femtosecond laser

    NASA Astrophysics Data System (ADS)

    Hughes, M. A.; Homewood, K. P.; Curry, R. J.; Ohishi, Y.; Suzuki, T.

    2014-07-01

    We report waveguides in Ni-doped Li2O-Ga2O3-SiO2 (Ni:LGS) glass and glass-ceramic (GC) fabricated with a femtosecond (fs) laser with repetition rate of 1 kHz. When the glass is annealed to form a GC, the waveguides are erased. However, in the GC the waveguides are not erased by annealing. In Ni:LGS GC a 415 nm absorption band was created by fs laser waveguide writing due to the creation of Ni nanoparticles with an estimated diameter of a few nm. Raman and photoluminescence spectra of the bulk and waveguide structures were indistinguishable; however, fluorescence decay profiles indicated more long lifetime components in the waveguide compared to the bulk.

  14. Optical and spectral studies on pure and europium doped olgite type Na(Sr,Ba)PO4 ceramics

    NASA Astrophysics Data System (ADS)

    Jawaher, K. Rackesh; Jagannathan, R.; Das, S. Jerome; Krishnan, S.

    2015-04-01

    Europium ion doped olgite type Na(Sr,Ba)PO4 ceramics, a new generation of light emitting bulb, was prepared by a high temperature solid-state reaction method. The synthesized materials were subjected to various characterizations such as X-ray powder diffraction, Scanning electron microscopy and FT-IR spectra measurements. The EPR spectrum of the sample exhibits a well-resolved hyperfine structure of 151Eu2+ and 153Eu2+ isotopes and the g value has been calculated. Fluorescence spectra revealed that europium ions were present in divalent as well as in the trivalent oxidation states. The critical distance for energy transfer between Eu2+ and Eu2+ ion is calculated as 20 Å, which is in good agreement with that of experimental data. The FTIR analysis reveals all the vibrations of PO43- ions.

  15. Luminescence properties of dual valence Eu doped nano-crystalline BaF2 embedded glass-ceramics and observation of Eu2+ → Eu3+ energy transfer.

    PubMed

    Biswas, Kaushik; Sontakke, Atul D; Sen, R; Annapurna, K

    2012-03-01

    Europium doped glass-ceramics containing BaF(2) nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and transmission electron microscopy have confirmed the presence of cubic BaF(2) nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline phase having low phonon energy of 346 cm(-1) has been demonstrated from the emission spectra of Eu(3+) ions showing the transitions from upper excitation states (5)D(J) (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu(3+)) ions to divalent (Eu(2+)) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further, the phenomenon of energy transfer from Eu(2+) to Eu(3+) ion by radiative trapping or re-absorption is evidenced which increases with the degree of ceramization. For the first time, the reduction of Eu(3+) to Eu(2+) under normal air atmospheric condition has been observed in a BaF(2) containing oxyfluoride glass-ceramics system.

  16. Effect of processing routes on microstructure, electrical and dielectric behavior of Mg-doped CaCu3Ti4O12 electro-ceramic

    NASA Astrophysics Data System (ADS)

    Singh, Laxman; Rai, U. S.; Mandal, K. D.; Rai, Alok Kumar

    2013-09-01

    In the present communication, data on magnesium-doped calcium copper titanate CaCu2.90Mg0.10Ti4O12 (CCMTO) electro-ceramic, synthesized by the semi-wet route (SWR), ball-milled route (BMR) and solid-state route (SSR), is characterized by TG-DTA, XRD, SEM, EDX and TEM techniques. XRD confirmed the formation of single phase in CCMTO ceramic. The CuO phase present at grain boundaries in SWR ceramic was shown by the SEM micrograph, which was verified by EDX. The TEM image of SWR ceramic shows nanocrystalline particles in the range 80±20 nm. The value of the dielectric constant of SWR ( ɛ r ˜20091) ceramic is higher than those of BMR and SSR ( ɛ r ˜1247) ceramics at 1 kHz at 450 K. A dielectric relaxation has been observed in the frequency range 100 Hz-100 kHz. The high-temperature dielectric dispersion shows one large low-frequency response and two Debye-type relaxations. The impedance and modulus studies show the highest grain-boundary resistance for BMR ceramic.

  17. Template-assisted formation of microsized nanocrystalline CeO2 tubes and their catalytic performance in the carboxylation of methanol

    PubMed Central

    Naumann, Meike; Schäfer, Christian; Brandner, Armin; Hofmann, Heiko J; Claus, Peter

    2011-01-01

    Summary Polymethylmethacrylate (PMMA)/ceria composite fibres were synthesized by using a sequential combination of polymer electrospinning, spray-coating with a sol, and a final calcination step to yield microstructured ceria tubes, which are composed of nanocrystalline ceria particles. The PMMA template is removed from the organic/inorganic hybrid material by radio frequency (rf) plasma etching followed by calcination of the ceramic green-body fibres. Microsized ceria (CeO2) tubes, with a diameter of ca. 0.75 µm, composed of nanocrystalline agglomerated ceria particles were thus obtained. The 1-D ceramic ceria material was characterized by X-ray diffraction, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV–vis and photoluminescence spectroscopy (PL), as well as thermogravimetric analysis (TGA). Its catalytic performance was studied in the direct carboxylation of methanol with carbon dioxide leading to dimethyl carbonate [(CH3O)2CO, DMC], which is widely employed as a phosgene and dimethyl sulfate substitute, and as well as a fuel additive. PMID:22259761

  18. Preparation and laser performance of Nd-doped yttrium lanthanum oxide transparent ceramic

    NASA Astrophysics Data System (ADS)

    Yang, Qiuhong; Lu, Shenzhou; Zhang, Bin; Zhang, Haojia; Zhou, Jun; Yuan, Zhijun; Qi, Yunfeng; Lou, Qihong

    2011-03-01

    1.5 at.% Nd:Y 1.8La 0.2O 3 transparent ceramic was fabricated by a solid-state reaction method and sintered at 1650-1700 °C for 40-50 h under H 2 atmosphere. The spectroscopic properties were investigated at room temperature. The transparent ceramic has excellent spectroscopic properties, with the absorption cross section of 1.50 × 10 -20 cm 2 and broad full width at half maximum (FWHM) of about 8 nm at LD wavelength 806 nm, the emission cross section of 2.03 × 10 -20 cm 2 at 1079 nm, and the decay lifetime of 200 μs. Laser performance was carried out using an uncoated Nd:Y 1.8La 0.2O 3 ceramic plate under laser diode end-pumping without any water cooling device. The room temperature thermal conductivity of this ceramic is 6.20 W/mK. For Nd:Y 1.8La 0.2O 3 ceramic laser, a maximum output power of 62 mW was obtained at 1079 nm under a 808 nm diode pump.

  19. Dual-functional CeO2:Eu3+ nanocrystals for performance-enhanced dye-sensitized solar cells.

    PubMed

    Roh, Jongmin; Hwang, Sun Hye; Jang, Jyongsik

    2014-11-26

    Single-crystalline, octahedral CeO2:Eu3+ nanocrystals, successfully prepared using a simple hydrothermal method, were investigated to determine their photovoltaic properties in an effort to enhance the light-harvesting efficiency of dye-sensitized solar cells (DSSCs). The size of the CeO2:Eu3+ nanocrystals (300-400 nm), as well as their mirrorlike facets, significantly improved the diffuse reflectance of visible light. Excitation of the CeO2:Eu3+ nanocrystal with 330 nm ultraviolet light was re-emitted via downconversion photoluminescence (PL) from 570 to 672 nm, corresponding to the 5D0→7FJ transition in the Eu3+ ions. Downconversion PL was dominant at 590 nm and had a maximum intensity for 1 mol % Eu3+. The CeO2:Eu3+ nanocrystal-based DSSCs exhibited a power conversion efficiency of 8.36%, an increase of 14%, compared with conventional TiO2 nanoparticle-based DSSCs, because of the strong light-scattering and downconversion PL of the CeO2:Eu3+ nanocrystals.

  20. Infiltration of Metal Substrates with Nanostructured CeO2 by a Room-Temperature Wet Process.

    PubMed

    Presto, Sabrina; Viviani, Massimo

    2015-05-01

    A room-temperature infiltration procedure for the deposition of CeO2 nanopowders on Ni-based foams employing stable CeO2 suspensions in water has been developed. It consists of a two-steps dipping process, the first in nanopowder suspension at pH 6.5 followed by further dipping into a NH3OH solution at pH 12. The pH shift represents a key factor to improve the homogeneity and dispersion of infiltrated powder by avoiding coalescence during the drying step. Water-based suspensions have been prepared starting from a commercial nanostructured CeO2. Powder was characterized by X-ray diffraction, particle size and specific surface area measurements, transmission electron microscopy. Stability of suspensions was studied by zeta potential measurements at low concentration, while sedimentation tests were carried out on highly concentrated suspensions as a function of pH, CeO2 amount and surfactant presence. Effect of CeO2 concentration, surfactant addition, pH value, substrate composition and microstructure were taken in account. Under best conditions, very homogeneous infiltrations could be obtained without any preferential orientation or agglomerates. Thermal stability of the composites infiltrated materials was also tested. The technique seems to be very promising in advanced nanostructured decorations and coating preparation.

  1. Investigation of trimethylacetic acid adsorption on stoichiometric and oxygen-deficient CeO2(111) surfaces.

    PubMed

    Sanghavi, Shail; Wang, Weina; Nandasiri, Manjula I; Karakoti, Ajay S; Wang, Wenliang; Yang, Ping; Thevuthasan, S

    2016-06-21

    We studied the interactions between the carboxylate anchoring group from trimethylacetic acid (TMAA) and CeO2(111) surfaces as a function of oxygen stoichiometry using in situ X-ray photoelectron spectroscopy (XPS). The stoichiometric CeO2(111) surface was obtained by annealing the thin film under 2.0 × 10(-5) Torr of oxygen at ∼550 °C for 30 min. In order to reduce the CeO2(111) surface, the thin film was annealed under ∼5.0 × 10(-10) Torr vacuum conditions at 550 °C, 650 °C, 750 °C and 850 °C for 30 min to progressively increase the oxygen defect concentration on the surface. The saturated TMAA coverage on the CeO2(111) surface determined from XPS elemental composition is found to increase with increasing oxygen defect concentration. This is attributed to the increase of under-coordinated cerium sites on the surface with the increase in the oxygen defect concentrations. XPS results were in agreement with periodic density functional theory (DFT) calculations and indicate a stronger binding between the carboxylate group from TMAA and the oxygen deficient CeO2-δ(111) surface through dissociative adsorption.

  2. Effects of CeO2 Support Facets on VOx/CeO2 Catalysts in Oxidative Dehydrogenation of Methanol

    SciTech Connect

    Li, Yan; Wei, Zhehao; Gao, Feng; Kovarik, Libor; Peden, Charles HF; Wang, Yong

    2014-05-13

    CeO2 supports with dominating facets, i.e., low index (100), (110) and (111) facets, are prepared. The facet effects on the structure and catalytic performance of supported vanadium oxide catalysts are investigated using oxidative dehydrogenation of methanol as a model reaction. In the presence of mixed facets, Infrared and Raman characterizations demonstrate that surface vanadia species preferentially deposit on CeO2 (100) facets, presumably because of its higher surface energy. At the same surface vanadium densities, VOx species on (100) facets show better dispersion, followed by (110) and (111) facets. The VOx species on CeO2 nanorods with (110) and (100) facets display higher activity and lower apparent activation energies compared to that on CeO2 nanopolyhedras with dominating (111) facets and CeO2 nanocubes with dominating (100) facets. The higher activity for VOx/CeO2(110) might be related to the more abundant oxygen vacancies present on the (110) facets, evidenced from Raman spectroscopic measurements.

  3. Investigation of trimethylacetic acid adsorption on stoichiometric and oxygen-deficient CeO2 (111) surfaces

    DOE PAGESBeta

    Sanghavi, Shail; Wang, Weina; Nandasiri, Manjula I.; Karakoti, Ajay S.; Wang, Wenliang; Yang, Ping; Thevuthasan, S.

    2016-05-12

    We studied the interactions between the carboxylate anchoring group from trimethylacetic acid (TMAA) and CeO2(111) surfaces as a function of oxygen stoichiometry using in situ X-ray photoelectron spectroscopy (XPS). The stoichiometric CeO2(111) surface was obtained by annealing the thin film under 2.0 × 10–5 Torr of oxygen at ~550 °C for 30 min. In order to reduce the CeO2(111) surface, the thin film was annealed under ~5.0 × 10–10 Torr vacuum conditions at 550 °C, 650 °C, 750 °C and 850 °C for 30 min to progressively increase the oxygen defect concentration on the surface. The saturated TMAA coverage onmore » the CeO2(111) surface determined from XPS elemental composition is found to increase with increasing oxygen defect concentration. This is attributed to the increase of under-coordinated cerium sites on the surface with the increase in the oxygen defect concentrations. Furthermore, XPS results were in agreement with periodic density functional theory (DFT) calculations and indicate a stronger binding between the carboxylate group from TMAA and the oxygen deficient CeO2–δ(111) surface through dissociative adsorption.« less

  4. Influence of two types of organic matter on interaction of CeO2 nanoparticles with plants in hydroponic culture.

    PubMed

    Schwabe, Franziska; Schulin, Rainer; Limbach, Ludwig K; Stark, Wendelin; Bürge, Diane; Nowack, Bernd

    2013-04-01

    An important aspect in risk assessment of nanoparticles (NPs) is to understand their environmental interactions. We used hydroponic plant cultures to study nanoparticle-plant-root interaction and translocation and exposed wheat and pumpkin to suspensions of uncoated CeO2-NP for 8d (primary particle size 17-100 nm, 100 mg L(-1)) in the absence and presence of fulvic acid (FA) and gum arabic (GA) as representatives of different types of natural organic matter. The behavior of CeO2-NPs in the hydroponic solution was monitored regarding agglomeration, sedimentation, particle size distribution, surface charge, amounts of root association, and translocation into shoots. NP-dispersions were stable over 8d in the presence of FA or GA, but with growing plants, changes in pH, particle agglomeration rate, and hydrodynamic diameter were observed. None of the plants exhibited reduced growth or any toxic response during the experiment. We found that CeO2-NPs translocated into pumpkin shoots, whereas this did not occur in wheat plants. The presence of FA and GA affected the amount of CeO2 associated with roots (pure>FA>GA) but did not affect the translocation factor. Additionally, we could confirm via TEM and SEM that CeO2-NPs adhered strongly to root surfaces of both plant species.

  5. Transformation of pristine and citrate-functionalized CeO2 nanoparticles in a laboratory-scale activated sludge reactor.

    PubMed

    Barton, Lauren E; Auffan, Melanie; Bertrand, Marie; Barakat, Mohamed; Santaella, Catherine; Masion, Armand; Borschneck, Daniel; Olivi, Luca; Roche, Nicolas; Wiesner, Mark R; Bottero, Jean-Yves

    2014-07-01

    Engineered nanomaterials (ENMs) are used to enhance the properties of many manufactured products and technologies. Increased use of ENMs will inevitably lead to their release into the environment. An important route of exposure is through the waste stream, where ENMs will enter wastewater treatment plants (WWTPs), undergo transformations, and be discharged with treated effluent or biosolids. To better understand the fate of a common ENM in WWTPs, experiments with laboratory-scale activated sludge reactors and pristine and citrate-functionalized CeO2 nanoparticles (NPs) were conducted. Greater than 90% of the CeO2 introduced was observed to associate with biosolids. This association was accompanied by reduction of the Ce(IV) NPs to Ce(III). After 5 weeks in the reactor, 44 ± 4% reduction was observed for the pristine NPs and 31 ± 3% for the citrate-functionalized NPs, illustrating surface functionality dependence. Thermodynamic arguments suggest that the likely Ce(III) phase generated would be Ce2S3. This study indicates that the majority of CeO2 NPs (>90% by mass) entering WWTPs will be associated with the solid phase, and a significant portion will be present as Ce(III). At maximum, 10% of the CeO2 will remain in the effluent and be discharged as a Ce(IV) phase, governed by cerianite (CeO2).

  6. The Interaction of Carbon Monoxide with Rhodium on Potassium-Modified CeO2(111)

    DOE PAGESBeta

    Mullins, David R.

    2016-02-03

    The adsorption and reactions of CO adsorbed on Rh particles deposited on K-covered CeO2(111) were studied by temperature programmed desorption and photoelectron spectroscopy. K deposited on CeO2(111) forms a KOX over-layer by extracting O from the ceria and partially reducing some of the Ce4+ to Ce3+. CO does not adsorb on the KOX / CeO2-X(111) surface in the absence of Rh particles. CO adsorbed on Rh / K / CeO2(111) adsorbs molecularly on the Rh at 200 K. As the surface is heated the CO spills-over and reacts with the KOX to form carbonate. The carbonate decomposes at elevated temperaturemore » to produce CO and CO2. The carbonate stabilizes the KOX so that K desorbs at a higher temperature than it would in the absence of CO. When the Rh and K deposition are reversed so that K is deposited on both the Rh and the CeO2(111), CO adsorbs as CO2- at 200 K. The CO2- decomposes below 350 K to produce gas phase CO and adsorbed CO32- and CO. The CO is stabilized by the K on the Rh and desorbs above 540 K. The carbonate decomposes into gas phase CO and CO2.« less

  7. An in vivo and in vitro toxicological characterization of realistic nanoscale CeO2 inhalation exposures

    PubMed Central

    Demokritou, Philip; Gass, Samuel; Pyrgiotakis, Georgios; Cohen, Joel M.; Goldsmith, William; McKinney, Walt; Frazer, David; Ma, Jane; Schwegler-Berry, Diane; Brain, Joseph; Castranova, Vincent

    2015-01-01

    Nanoscale CeO2 is increasingly used for industrial and commercial applications, including catalysis, UV-shielding, and as an additive in various nanocomposites. Because of its increasing potential for consumer and occupational exposures, a comprehensive toxicological characterization of this nanomaterial is needed. Preliminary results from intratracheal instillation studies in rats point to cytoxicity and inflammation, though these studies may not accurately use realistic nanoscale exposure profiles. In contrast, published in vitro cellular studies have reported limited toxicological outcomes for the case of nano-ceria. Here, we present an integrative study evaluating the toxicity of nanoscale CeO2 both in vitro, using the A549 lung epithelial cell line, and in vivo using an intact rat model. Realistic nano-ceria exposure atmospheres were generated using the Harvard Versatile Engineered Nanomaterial Generation System (VENGES), and rats were exposed via inhalation. Finally, the use of a nanothin amorphous SiO2 encapsulation coating as a means of mitigating CeO2 toxicity was assessed. Results from the inhalation experiments show lung injury and inflammation with increased PMN and LDH levels in the bronchoalveolar lavage fluid of the CeO2 exposed rats. Moreover, exposure to SiO2-coated CeO2 did not induce any pulmonary toxicity to the animals, representing clear evidence for the safe by design SiO2-encapsualtion concept. PMID:23061914

  8. Different synthesis protocols for Co3O4 -CeO2 catalysts--part 1: influence on the morphology on the nanoscale.

    PubMed

    Yang, Jingxia; Lukashuk, Liliana; Akbarzadeh, Johanna; Stöger-Pollach, Michael; Peterlik, Herwig; Föttinger, Karin; Rupprechter, Günther; Schubert, Ulrich

    2015-01-01

    Co3 O4 -modified CeO2 (Co/Ce 1:4) was prepared by a combination of sol-gel processing and solvothermal treatment. The distribution of Co was controlled by means of the synthesis protocol to yield three different morphologies, namely, Co3 O4 nanoparticles located on the surface of CeO2 particles, coexistent Co3 O4 and CeO2 nanoparticles, or Co oxide structures homogeneously distributed within CeO2 . The effect of the different morphologies on the properties of Co3 O4 -CeO2 was investigated with regard to the crystallite phase(s), particle size, surface area, and catalytic activity for CO oxidation. The material with Co3 O4 nanoparticles finely dispersed on the surface of CeO2 particles had the highest catalytic activity.

  9. Performance of Europium-Doped Strontium Iodide, Transparent Ceramics and Bismuth-loaded Polymer Scintillators

    SciTech Connect

    Cherepy, N J; Payne, S A; Sturm, B W; O'Neal, S P; Seeley, Z M; Drury, O B; Haselhorst, L K; Rupert, B L; Sanner, R D; Thelin, P A; Fisher, S E; Hawrami, R; Shah, K S; Burger, A; Ramey, J O; Boatner, L A

    2011-08-30

    Recently discovered scintillators for gamma ray spectroscopy, single crystal SrI{sub 2}(Eu), GYGAG(Ce) transparent ceramic and Bismuth-loaded plastics, offer resolution and fabrication advantages compared to commercial scintillators, such as NaI(Tl) and standard PVT plastic. Energy resolution at 662 keV of 2.7% is obtained with SrI{sub 2}(Eu), while 4.5% is obtained with GYGAG(Ce). A new transparent ceramic scintillator for radiographic imaging systems, GLO(Eu) offers high light yield of 70,000 Photons/MeV, high stopping, and low radiation damage. Implementation of single crystal SrI{sub 2}(Eu), Gd-based transparent ceramics, and Bi-loaded plastic scintillators can advance the state-of-the art in ionizing radiation detection systems.

  10. Microstructural and physical properties of magnesium oxide-doped silicon nitride ceramics

    NASA Astrophysics Data System (ADS)

    Sirota, V.; Lukianova, O.; Krasilnikov, V.; Selemenev, V.; Dokalov, V.

    Silicon nitride based ceramics with aluminum, yttrium and magnesium oxides were produced by cold isostatic pressing and free sintering. The phase composition of the starting MgO powder obtained by the novel technology has been studied. The effect of magnesium oxide content on the structure of the produced materials has been investigated. It was found, that obtained materials with 1 and 2 wt.% of magnesium oxide and without it have a typical β-silicon nitride structure with elongated grains. Ceramics with 5 wt.% magnesia has a duplex α/β-structure with elongated and equiaxed grains. Ceramics with 2 wt.% magnesium oxide has a maximum density of 2.91 g/cm3. The increases in magnesium oxide content upto 5% led to decrease in the shrinkage (from 16% to 12%) and density (from 2.88 to 2.37 g/cm3).

  11. Energy transfer kinetics in oxy-fluoride glass and glass-ceramics doped with rare-earth ions

    SciTech Connect

    Sontakke, Atul D.; Annapurna, K.

    2012-07-01

    An investigation of donor-acceptor energy transfer kinetics in dual rare earths doped precursor oxy-fluoride glass and its glass-ceramics containing NaYF{sub 4} nano-crystals is reported here, using three different donor-acceptor ion combinations such as Nd-Yb, Yb-Dy, and Nd-Dy. The precipitation of NaYF{sub 4} nano-crystals in host glass matrix under controlled post heat treatment of precursor oxy-fluoride glasses has been confirmed from XRD, FESEM, and transmission electron microscope (TEM) analysis. Further, the incorporation of dopant ions inside fluoride nano-crystals has been established through optical absorption and TEM-EDX analysis. The noticed decreasing trend in donor to acceptor energy transfer efficiency from precursor glass to glass-ceramics in all three combinations have been explained based on the structural rearrangements that occurred during the heat treatment process. The reduced coupling phonon energy for the dopant ions due to fluoride environment and its influence on the overall phonon assisted contribution in energy transfer process has been illustrated. Additionally, realization of a correlated distribution of dopant ions causing clustering inside nano-crystals has also been reported.

  12. Mössbauer spectroscopy of europium-doped fluorochlorozirconate glasses and glass ceramics: optimization of storage phosphors in computed radiography

    PubMed Central

    Pfau, C; Paßlick, C; Gray, S; Johnson, JA; Johnson, CE; Schweizer, S

    2013-01-01

    Eu2+-doped fluorochlorozirconate (FCZ) glasses and glass ceramics, which are being developed for medical and photovoltaic applications, have been analysed by Mössbauer spectroscopy. The oxidation state and chemical environment of the europium ions, which are important for the performance of these materials, were investigated. Routes for maximizing the divalent europium content were investigated. By using EuCl2 instead of EuF2 in the starting material a fraction of about 90% of the europium was maintained in the Eu2+ state as opposed to about 70% when using EuF2. The glass ceramics produced by subsequent thermal processing contain BaCl2 nanocrystals in which Eu2+ is incorporated, as shown by the narrower linewidth in the Mössbauer spectrum. Debye temperatures of 147 K and 186 K for Eu2+ and Eu3+, respectively, were determined from temperature dependent Mössbauer measurements. The f-factors were used to obtain the Eu2+/Eu3+ ratio from the area ratio of the corresponding absorption lines. PMID:23603535

  13. Synthesis of Cr-doped CaTiSiO{sub 5} ceramic pigments by spray drying

    SciTech Connect

    Lyubenova, T. Stoyanova Matteucci, F.; Costa, A.L.; Dondi, M.; Ocana, M.

    2009-04-02

    Cr-doped CaTiSiO{sub 5} was synthesized by spray drying and conventional ceramic method in order to assess its potential as ceramic pigment. The evolution of the phase composition with thermal treatment was investigated by X-ray powder diffraction (XRPD) and thermal analyses (DTA-TGA-EGA). Powder morphology and particle size distribution were analyzed by scanning electron microscopy (SEM) and laser diffraction, respectively. The color efficiency of pigments was evaluated by optical spectroscopy (UV-vis-NIR) and colorimetric analysis (CIE Lab). Results proved that spray drying is an efficient procedure to prepare highly reactive pigment precursors. The spray-dried powders consist of hollow spherical particles with aggregate size in the 1-10 {mu}m range, developing a brown coloration. Optical spectra reveal the occurrence of Cr(III) and Cr(IV), both responsible for the brown color of this pigment. The former occupies the octahedral site of titanite, in substitution of Ti(IV), while the latter is located at the tetrahedral site, where replaces Si(IV)

  14. αTCP ceramic doped with dicalcium silicate for bone regeneration applications prepared by powder metallurgy method: in vitro and in vivo studies.

    PubMed

    Velasquez, Pablo; Luklinska, Zofia B; Meseguer-Olmo, Luis; Mate-Sanchez de Val, Jose E; Delgado-Ruiz, Rafael A; Calvo-Guirado, Jose L; Ramirez-Fernandez, Ma P; de Aza, Piedad N

    2013-07-01

    This study reports on the in vitro and in vivo behavior of α-tricalcium phosphate (αTCP) and also αTCP doped with either 1.5 or 3.0 wt % of dicalcium silicate (C2 S). The ceramics were successfully prepared by powder metallurgy method combined with homogenization and heat treatment procedures. All materials were composed of a single-phase, αTCP in the case of a pure material, or solid solution of C2 S in αTCP for the doped αTCP, which were stable at room temperature. The ceramics were tested for bioactivity in simulated body fluid, cell culture medium containing adult mesenchymal stem cells of human origin, and in animals. Analytical scanning electron microscopy combined with chemical elemental analysis was used and Fourier transform infrared and conventional histology methods. The in vivo behavior of the ceramics matched the in vitro results, independently of the C2 S content in αTCP. Carbonated hydroxyapatite (CHA) layer was formed on the surface and within the inner parts of the specimens in all cases. A fully mineralized new bone growing in direct contact with the implants was found under the in vivo conditions. The bioactivity and biocompatibility of the implants increased with the C2 S content in αTCP. The C2 S doped ceramics also favoured a phase transformation of αTCP into CHA, important for full implant integration during the natural bone healing processes. αTCP ceramic doped with 3.0 wt % C2 S showed the best bioactive in vitro and in vivo properties of all the compositions and hence could be of interest in specific applications for bone restorative purposes.

  15. A comparative study of CeO2-Al2O3 support prepared with different methods and its application on MoO3/CeO2-Al2O3 catalyst for sulfur-resistant methanation

    NASA Astrophysics Data System (ADS)

    Jiang, Minhong; Wang, Baowei; Yao, Yuqin; Li, Zhenhua; Ma, Xinbin; Qin, Shaodong; Sun, Qi

    2013-11-01

    The CeO2-Al2O3 supports prepared with impregnation (IM), deposition precipitation (DP), and solution combustion (SC) methods for MoO3/CeO2-Al2O3 catalyst were investigated in the sulfur-resistant methanation. The supports and catalysts were characterized by N2-physisorption, transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy (RS), and temperature-programmed reduction (TPR). The N2-physisorption results indicated that the DP method was favorable for obtaining better textural properties. The TEM and RS results suggested that there is a CeO2 layer on the surface of the support prepared with DP method. This CeO2 layer not only prevented the interaction between MoO3 and γ-Al2O3 to form Al2(MoO4)3 species, but also improved the dispersion of MoO3 in the catalyst. Accordingly, the catalysts whose supports were prepared with DP method exhibited the best catalytic activity. The catalysts whose supports were prepared with SC method had the worst catalytic activity. This was caused by the formation of Al2(MoO4)3 and crystalline MoO3. Additionally, the CeO2 layer resulted in the instability of catalysts in reaction process. The increasing of calcination temperature of supports reduced the catalytic activity of all catalysts. The decrease extent of the catalysts whose supports were prepared with DP method was the lowest as the CeO2 layer prevented the interaction between MoO3 and γ-Al2O3.

  16. Effects of gallia addition on sintering behavior and electrical conductivity of yttria-doped ceria

    NASA Astrophysics Data System (ADS)

    Seo, Seung-Woo; Park, Ji-Hoon; Park, Min-Woo; Koo, Ji-Hoon; Lee, Ki-Tae; Lee, Joo-Sin

    2014-07-01

    The densification behavior and electrical conductivity of Ce0.8Y0.2O1.9 ceramics with gallia concentrations ranging from 0 to 5 mol. % were investigated. The sintered density was found to increase with increasing Ga2O3 content up to 1 mol. % and then to decrease upon further Ga2O3 addition. Dense Ce0.8Y0.2O1.9 ceramics with 94% of the theoretical density could be obtained by sintering the milled mixture with 1 mol. % Ga2O3 addition at 1400°C for 5 h. The conductivity of the 1 mol. % Ga2O3-added specimen showed a maximum value of 1.37 × 10-2 Ω-1· cm-1 at 700°C. Pure Ce0.8Y0.2O1.9 ceramics needed to be sintered at 1550°C in order to obtain an equivalent theoretical density and conductivity. The introduction of Ga2O3 doping had a good effect on the sintering properties and electrical conductivities of Y2O3-doped CeO2.

  17. Microstructure and dielectric properties of BaTiO{sub 3} ceramic doped with yttrium, magnesium, gallium and silicon for AC capacitor application

    SciTech Connect

    Wang, Min-Jia; Yang, Hui; Zhang, Qi-Long; Lin, Zhi-Sheng; Zhang, Zi-Shan; Yu, Dan; Hu, Liang

    2014-12-15

    Graphical abstract: Core–shell structure can be obtained in BaTiO{sub 3} ceramics co-doped with Y–Mg-Ga-Si. Y-Mg-Ga-Si co-dopant can obviously reduce dielectric loss, improve AC breakdown voltage and flatten temperature dependence of capacitance curve. - Highlights: • Y-Mg-Ga-Si co-doped BaTiO{sub 3} ceramics with core-shell structure were prepared. • Y{sup 3+}, Mg{sup 2+}, and Ga{sup 3+} dissolved in the lattice BaTiO{sub 3} replacing Ba{sup 2+} site or Ti{sup 4+} site. • Y{sup 3+} and Ga{sup 3+} tended to remain close to the grain boundaries as a shell maker. • Y-Mg-Ga-Si co-doped BaTiO{sub 3} ceramics show high AC breakdown voltage and low tanδ. - Abstract: The microstructures and dielectric properties of Y-Mg-Ga-Si co-doped barium titanate ceramics were investigated. Y{sup 3+} dissolved in the lattice of BaTiO{sub 3} replacing both Ba{sup 2+} site and Ti{sup 4+} site, and Mg{sup 2+} replaced Ti{sup 4+} site. The replacements of Y{sup 3+} and Mg{sup 2+} inhibit the grain growth, cause tetragonal-to-pseudocubic phase transition, reduce the dielectric loss, and flatten the temperature dependence of capacitance curve. The incorporation of Ga{sup 3+} can improve sintering and increase permittivity. Y{sup 3+} and Ga{sup 3+} tended to remain close to the grain boundaries, and play an important role as a shell maker in the formation of the core–shell structure in the co-doped BaTiO{sub 3} ceramics. Excellent dielectric properties: ϵ{sub r} = ∼2487, tanδ = ∼0.7% (at 1 kHz), ΔC/C{sub 25} < ∼6.56% (from −55 °C to 125 °C) and alternating current breakdown voltage E < ∼4.02 kV/mm can be achieved in the BaTiO{sub 3}–0.02Y{sub 2}O{sub 3}–0.03MgO–0.01Ga{sub 2}O{sub 3}–0.005SiO{sub 2} ceramics sintered at 1380 °C. This material has a potential application in alternating current multilayer ceramic capacitor.

  18. Observation of an anomalous correlation between permittivity and tunability of a doped (Ba,Sr)TiO3 ferroelectric ceramic developed for microwave applications

    NASA Astrophysics Data System (ADS)

    Kozyrev, Andrey B.; Kanareykin, Alexei D.; Nenasheva, Elizaveta A.; Osadchy, Vitaly N.; Kosmin, Dmitry M.

    2009-07-01

    Anomalous dependencies of the dynamic (pulse) and static tunability [k(U )=C(0)/C(U)] as a function of permittivity (ɛ) were observed in ferroelectric varactors based on doped paraelectric state (Ba,Sr)TiO3 ceramics. The reduction of the relatively high permittivity value from ɛ ≅810 down to ɛ ≅260 by introducing various proportions of a Mg2TiO4 additive resulted in a 20% increase in tunability. Furthermore, ceramics with this additive have demonstrated dynamic tunability noticeably higher than the static tunability, also unexpected for this type of material.

  19. Facile and Mild Strategy to Construct Mesoporous CeO2-CuO Nanorods with Enhanced Catalytic Activity toward CO Oxidation.

    PubMed

    Chen, Guozhu; Xu, Qihui; Yang, Ying; Li, Cuncheng; Huang, Taizhong; Sun, Guoxin; Zhang, Shuxiang; Ma, Dongling; Li, Xu

    2015-10-28

    CeO2-CuO nanorods with mesoporous structure were synthesized by a facile and mild strategy, which involves an interfacial reaction between Ce2(SO4)3 precursor and NaOH ethanol solution at room temperature to obtain mesoporous CeO2 nanorods, followed by a solvothermal treatment of as-prepared CeO2 and Cu(CH3COO)2. Upon solvothermal treatment, CuO species is highly dispersed onto the CeO2 nanorod surface to form CeO2-CuO composites, which still maintain the mesoporous feature. A preliminary CO catalytic oxidation study demonstrated that the CeO2-CuO samples exhibited strikingly high catalytic activity, and a high CO conversion rate was observed without obvious loss in activity even after thermal treatment at a high temperature of 500 °C. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H2-TPR) analysis revealed that there is a strong interaction between CeO2 and CuO. Moreover, it was found that the introduction of CuO species into CeO2 generates oxygen vacancies, which is highly likely to be responsible for high catalytic activity toward CO oxidation of the mesoporous CeO2-CuO nanorods.

  20. Facile preparation of well-dispersed CeO2-ZnO composite hollow microspheres with enhanced catalytic activity for CO oxidation.

    PubMed

    Xie, Qingshui; Zhao, Yue; Guo, Huizhang; Lu, Aolin; Zhang, Xiangxin; Wang, Laisen; Chen, Ming-Shu; Peng, Dong-Liang

    2014-01-01

    In this article, well-dispersed CeO2-ZnO composite hollow microspheres have been fabricated through a simple chemical reaction followed by annealing treatment. Amorphous zinc-cerium citrate hollow microspheres were first synthesized by dispersing zinc citrate hollow microspheres into cerium nitrate solution and then aging at room temperature for 1 h. By calcining the as-produced zinc-cerium citrate hollow microspheres at 500 °C for 2 h, CeO2-ZnO composite hollow microspheres with homogeneous composition distribution could be harvested for the first time. The resulting CeO2-ZnO composite hollow microspheres exhibit enhanced activity for CO oxidation compared with CeO2 and ZnO, which is due to well-dispersed small CeO2 particles on the surface of ZnO hollow microspheres and strong interaction between CeO2 and ZnO. Moreover, when Au nanoparticles are deposited on the surface of the CeO2-ZnO composite hollow microspheres, the full CO conversion temperature of the as-produced 1.0 wt % Au-CeO2-ZnO composites reduces from 300 to 60 °C in comparison with CeO2-ZnO composites. The significantly improved catalytic activity may be ascribed to the strong synergistic interplay between Au nanoparticles and CeO2-ZnO composites.

  1. Broadband near-infrared emission from Tm{sup 3+}/Er{sup 3+} co-doped nanostructured glass ceramics

    SciTech Connect

    Chen Daqin; Wang Yuansheng; Bao Feng; Yu Yunlong

    2007-06-01

    Transparent SiO{sub 2}-Al{sub 2}O{sub 3}-NaF-YF{sub 3} glass ceramics co-doped with Er{sup 3+} and Tm{sup 3+} were prepared by melt quenching and subsequent heating. X-ray diffraction and transmission electron microscopy experiments revealed that {beta}-YF{sub 3} nanocrystals incorporated with Er{sup 3+} and Tm{sup 3+} were precipitated homogeneously among the oxide glass matrix. An integrated broad near-infrared emission band in the wavelength region of 1300-1700 nm, consisting of Tm{sup 3+} emissions around 1472 nm ({sup 3}H{sub 4}{yields}{sup 3}F{sub 4}) and 1626 nm ({sup 3}F{sub 4}{yields}{sup 3}H{sub 6}), and Er{sup 3+} emission around 1543 nm ({sup 4}I{sub 13/2}{yields}{sup 4}I{sub 15/2}), was obtained under 792 nm laser excitation. The full width at half maximum of this integrated band increased with the increasing of [Tm]/[Er] ratio, and it reached as large as 175 nm for the 0.1 mol% Er{sup 3+} and 0.8 mol% Tm{sup 3+} co-doped sample. The energy transfers between Er{sup 3+} and Tm{sup 3+} were proposed to play an important role in tailoring the emission bandwidth of the sample.

  2. Soft and hybrid-doped Pb(Zr,Ti)O{sub 3} ceramics under stress, electric field, and temperature loading

    SciTech Connect

    Suchanicz, J.; Kim-Ngan, N.-T.; Konieczny, K.; Jankowska-Sumara, I.; Balogh, A. G.

    2011-05-15

    We investigated the influence of uniaxial pressure (0-1000 bars) applied parallelly or perpendicularly to the ac or dc electric field (in a one-dimensional or two-dimensional manner) on dielectric and ferroelectric properties of selected soft and hybrid-doped PZT ceramics (1 mol. % Gd, 1 mol. % La and 1 mol. % (La+Fe)-doped Pb(Zr{sub 0.54}Ti{sub 0.46}) O{sub 3}). Applying uniaxial pressure leads to a reduction of the peak intensity of the electric permittivity ({epsilon}), of the frequency dispersion, and of the dielectric hysteresis. The peak intensity of {epsilon} becomes diffused and shifts to a higher temperatures with increasing pressure. Simultaneous application of uniaxial pressure and dc electric field (perpendicular to each other) in the poling process implies in improvement of the ferroelectric properties, indicating a new possibility for poling materials with a high coercive field and/or high electric conductivity. It was also found that simultaneous application of uniaxial pressure and dc electric field (perpendicular to each other) allowed observation of the space charge in the depolarization process. The electrostrictive coefficient Q{sub 11} and differential permittivity were evaluated from obtained data. Our results show that applying uniaxial pressure induces similar effects as increasing the Ti-ion concentration in the PZT system. We interpreted our results based on the Cochran soft-mode and domain switching processes under the action of pressure.

  3. ARTICLES: Synthesis of Biomorphic ZrO2-CeO2 Nanostructures by Silkworm Silk Template

    NASA Astrophysics Data System (ADS)

    Zhang, Zong-jian; Li, Jia; Sun, Fu-sheng; Dickon, H. L. Ng; Luen Kwong, Fung

    2010-06-01

    A simple and green technique has been developed to prepare hierarchical biomorphic ZrO2-CeO2, using silkworm silk as the template. Different from traditional immersion technics, the whole synthesis process depends more on the restriction or direction functions of the silkworm silk template. The analytic results showed that ZrO2-CeO2 exhibited a well-crystallized hierarchically interwoven hollow fiber structure with 16-28 μm in diameter. The grain size of the sample calcined at 800 °C was about 14 nm. Consequently, the interwoven meshwork at three dimensions is formed due to the direction of biotemplate. The action mechanism is summarily discussed here. It may bring the biomorphic ZrO2-CeO2 nanomaterials with hierarchical interwoven structures to more applications, such as catalysts.

  4. Stability and migration of charged oxygen interstitials in ThO2 and CeO2

    SciTech Connect

    Xiao, Haiyan; Zhang, Yanwen; Weber, William J

    2013-01-01

    Density functional theory calculations have been carried out to study the stability and migration of charged oxygen interstitial in ThO2 and CeO2. The calculations demonstrate that the oxygen interstitial is likely to lose electrons under p-type conditions and gain electrons under n-type conditions. Neutral (Osplit0) and singly positive (Osplit+) O-O<110> split interstitials, and doubly negative octahedral (Oocta.2-) oxygen interstitial are found to be the lowest-energy configurations within a certain Fermi energy range. In both oxides, the Osplit+ is the most mobile, and the migration energies of the split oxygen interstitials in ThO2 are lower than in CeO2, indicating high oxygen interstitial mobility in ThO2 than in CeO2.

  5. Mild activation of CeO2-supported gold nanoclusters and insight into the catalytic behavior in CO oxidation

    NASA Astrophysics Data System (ADS)

    Li, Weili; Ge, Qingjie; Ma, Xiangang; Chen, Yuxiang; Zhu, Manzhou; Xu, Hengyong; Jin, Rongchao

    2016-01-01

    We report a new activation method and insight into the catalytic behavior of a CeO2-supported, atomically precise Au144(SR)60 nanocluster catalyst (where thiolate -SR = -SCH2CH2Ph) for CO oxidation. An important finding is that the activation of the catalyst is closely related to the production of active oxygen species on CeO2, rather than ligand removal of the Au144(SR)60 clusters. A mild O2 pretreatment (at 80 °C) can activate the catalyst, and the addition of reductive gases (CO or H2) can enhance the activation effects of O2 pretreatment via a redox cycle in which CO could reduce the surface of CeO2 to produce oxygen vacancies--which then adsorb and activate O2 to produce more active oxygen species. The CO/O2 pulse experiments confirm that CO is adsorbed on the cluster catalyst even with ligands on, and active oxygen species present on the surface of the pretreated catalyst reacts with CO pulses to generate CO2. The Au144(SR)60/CeO2 exhibits high CO oxidation activity at 80 °C without the removal of thiolate ligands. The surface lattice-oxygen of the support CeO2 possibly participates in the oxidation of CO over the Au144(SR)60/CeO2 catalyst.We report a new activation method and insight into the catalytic behavior of a CeO2-supported, atomically precise Au144(SR)60 nanocluster catalyst (where thiolate -SR = -SCH2CH2Ph) for CO oxidation. An important finding is that the activation of the catalyst is closely related to the production of active oxygen species on CeO2, rather than ligand removal of the Au144(SR)60 clusters. A mild O2 pretreatment (at 80 °C) can activate the catalyst, and the addition of reductive gases (CO or H2) can enhance the activation effects of O2 pretreatment via a redox cycle in which CO could reduce the surface of CeO2 to produce oxygen vacancies--which then adsorb and activate O2 to produce more active oxygen species. The CO/O2 pulse experiments confirm that CO is adsorbed on the cluster catalyst even with ligands on, and active oxygen species present on the surface of the pretreated catalyst reacts with CO pulses to generate CO2. The Au144(SR)60/CeO2 exhibits high CO oxidation activity at 80 °C without the removal of thiolate ligands. The surface lattice-oxygen of the support CeO2 possibly participates in the oxidation of CO over the Au144(SR)60/CeO2 catalyst. Electronic supplementary information (ESI) available. See DOI: 10.1039/C5NR07498C

  6. Effect of Yttrium Doping in Barium Zirconium Titanate Ceramics: A Structural, Impedance, and Modulus Spectroscopy Study

    NASA Astrophysics Data System (ADS)

    Badapanda, Tanmaya; Cavalcante, Laécio Santos; da Luz, Geraldo Eduardo; Batista, Nouga Cardoso; Anwar, Shahid; Longo, Elson

    2013-09-01

    In the current article, we studied the effect of yttrium [Y3+] ions' substitution on the structure and electric behavior of barium zirconate titanate (BZT) ceramics with a general formula [Ba1- x Y2 x/3](Zr0.25Ti0.75)O3 (BYZT) with [ x = 0, 0.025, and 0.05] which were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that these ceramics have a single phase with a perovskite-type cubic structure. Rietveld refinement data confirmed [BaO12], [ZrO6], [TiO6], and [YO6] clusters in the cubic lattice. The Y3+ ions' effects on the electric conductivity behavior of BZT ceramics as a function of temperature and frequency are described, which are based on impedance spectroscopy analyses. The complex impedance plots display a double semicircle which highlights the influences of grain and grain boundary on the ceramics. Impedance analyses showed that the resistance decreased with the increasing temperature and resulted in a negative temperature coefficient of the resistance property in all compositions. Modulus plots represent a non-Debye-type dielectric relaxation which is related to the grain and grain boundary as well as temperature-dependent electric relaxation phenomenon and an enhancement in the mobility barrier by Y3+ ions. Moreover, the electric conductivity increases with the replacement of Ba2+ by Y3+ ions may be due to the rise in oxygen vacancies.

  7. Fabrication and spectral properties of Nd 3+-doped yttrium lanthanum oxide transparent ceramics

    NASA Astrophysics Data System (ADS)

    Hu, Xiaoman; Yang, Qiuhong; Dou, Chuanguo; Xu, Jun; Zhou, Hongxu

    2008-06-01

    Transparent 1 at% Nd3+:Y1.9La0.1O3 ceramics were fabricated with nanopowders prepared by carbonate coprecipitation method. The powder compacts were sintered in H2 atmosphere at 1550 °C for 30 h. The Nd3+:Y1.9La0.1O3 ceramics display uniform grains of about 50 μm and high transparency. The highest transmittance of the ceramics reaches 67%. The strongest absorption peak is in the wavelength of 820 nm with absorption cross section of 2.48 × 10-20 cm2. The absorption is still high at LD wavelength 806 nm with absorption cross section of 1.78 × 10-20 cm2 and broad full width at half maximum (FWHM) of about 6.3 nm. The strongest emission peak was centered at 1078 nm with large stimulated emission cross section of 9.63 × 10-20 cm2 and broad FWHM of about 7.8 nm. The broad absorption and emission bandwidth of Nd3+:Y1.9La0.1O3 transparent ceramics are favorable to achieve the miniaturized LD pumping apparatus and ultrashort modelocked pulse laser output, respectively.

  8. Controllable synthesis of CeO2/g-C3N4 composites and their applications in the environment.

    PubMed

    She, Xiaojie; Xu, Hui; Wang, Hefei; Xia, Jiexiang; Song, Yanhua; Yan, Jia; Xu, Yuanguo; Zhang, Qi; Du, Daolin; Li, Huaming

    2015-04-21

    This research has developed a photocatalytic reactor that includes circulating water, light, and a temperature control system. CeO2/g-C3N4 composites with high photocatalytic activity and stability were synthesized by a simple and facile hydrothermal method. The obtained photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that in the CeO2/g-C3N4 composites, the CeO2 nanoparticles were homogeneously cubic in shape (from 3 to 10 nm) and were evenly dispersed on the surface of the g-C3N4. At constant temperature (30 °C), 5% CeO2/g-C3N4 photocatalyst showed the best photocatalytic activity for degrading organic dye methylene blue (MB) under visible light irradiation. The photocatalytic reaction for degrading MB followed first-order kinetics and 5% CeO2/g-C3N4 exhibited a higher apparent rate of 1.2686 min(-1), 7.8 times higher than that of the pure g-C3N4 (0.1621 min(-1)). In addition, it was found that 5% CeO2/g-C3N4 had a new property that it could be used as a sensor for the determination of trace amounts of Cu(2+). Such unique design and one-step synthesis, with an exposed high-activity surface, are important for both technical applications and theoretical investigations.

  9. Interfacial interactions of semiconductor with graphene and reduced graphene oxide: CeO2 as a case study.

    PubMed

    Xu, Liang; Huang, Wei-Qing; Wang, Ling-Ling; Huang, Gui-Fang

    2014-11-26

    The pursuit of superb building blocks of light harvesting systems has stimulated increasing efforts to develop graphene (GR)-based semiconductor composites for solar cells and photocatalysts. One critical issue for GR-based composites is understanding the interaction between their components, a problem that remains unresolved after intense experimental investigation. Here, we use cerium dioxide (CeO2) as a model semiconductor to systematically explore the interaction of semiconductor with GR and reduced graphene oxide (RGO) with large-scale ab initio calculations. The amount of charge transferred at the interfaces increases with the concentration of O atoms, demonstrating that the interaction between CeO2 and RGO is much stronger than that between CeO2 and GR due to the decrease of the average equilibrium distance between the interfaces. The stronger interaction between semiconductor and RGO is expected to be general, as evidenced by the results of two paradigms of TiO2 and Ag3PO4 coupled with RGO. The interfacial interaction can tune the band structure: the CeO2(111)/GR interface is a type-I heterojunction, while a type-II staggered band alignment exists between the CeO2(111) surface and RGO. The smaller band gap, type-II heterojunction, and negatively charged O atoms on the RGO as active sites are responsible for the enhanced photoactivity of CeO2/RGO composite. These findings can rationalize the available experimental reports and enrich our understanding of the interaction of GR-based composites for developing high-performance photocatalysts and solar cells.

  10. Crystallization of cerium containing iron borophosphate glasses/glass-ceramics and their spectral properties

    NASA Astrophysics Data System (ADS)

    Wang, Fu; Liao, Qilong; Zhu, Hanzhen; Dai, Yunya; Wang, Hong

    2016-04-01

    The crystallization behaviors of CeO2 containing 36Fe2O3-10B2O3-54P2O5 glasses/glass-ceramics (IBP glasses/glass-ceramics) and the effect of CeO2 addition on the structure of the IBP glasses/glass-ceramics annealed at 850 °C for 10 h were investigated by XRD, SEM and FTIR. The results show that Fe4(PO4)2O and Fe2(PO4)O phases are detected in the IBP glasses/glass-ceramics annealed at 650 °C for 10 h, and traces of FePO4 crystal is also detected when the CePO4 crystallite pre-exists in the unannealed IBP glass-ceramics. When the glasses/glass-ceramics are heat-treated at 850 °C for 10 h, Fe4(PO4)2O, Fe2(PO4)O and a small amount of FePO4 phase are detected. Meanwhile, CePO4 phase also appears in the crystallized IBP glasses/glass-ceramics containing more than 6 mol% (including 6 mol%) CeO2. Moreover, the main structural units of the crystallized glasses/glass-ceramics are [PO4] and [BO4] tetrahedron. [CeO4] tetrahedron also exists in the structure of the crystallized IBP glasses/glass-ceramics containing CeO2. CeO2 addition and the pre-existing CePO4 crystallite improve the resistance of the IBP glasses/glass-ceramics to crystallization, which makes the infrared bands associated with the vibration of [PO4] group increase in intensity and shift to high wave number.

  11. Compact diode stack end pumped Nd:YAG amplifier using core doped ceramics.

    PubMed

    Denis, Thomas; Hahn, Sven; Mebben, Sandra; Wilhelm, Ralf; Kolleck, Christian; Neumann, Jörg; Kracht, Dietmar

    2010-02-10

    We report on a compact Nd:YAG amplifier emitting a maximum pulse energy of 14 mJ. By amplifying a passively Q-switched oscillator (M(2)<1.2) a good beam quality of M(2) approximately 1.7 was achieved. The amplifier is diode pumped by an 8 bar diode stack of 800 W power and a nonimaging optic. This optic homogenizes the pump light and transfers it into a 5 mm diameter core doped rod with a centrally neodymium doped region of 3 mm and a samarium doped YAG cladding. We show that this cladding reduces parasitic effects in the laser rod compared to an undoped YAG cladding. Finally, we compare the compact amplifier with an amplifier, which is mode selectively pumped by a fiber coupled pump diode.

  12. Bulk and Interface Thermodynamics of Calcia-, and Yttria-doped Zirconia Ceramics: Nanograined Phase Stability

    NASA Astrophysics Data System (ADS)

    Drazin, John Walter

    Calcia-, and yttria- doped zirconia powders and samples are essential systems in academia and industry due to their observed bulk polymorphism. Pure zirconia manifests as Baddeleyite, a monoclinic structured mineral with 7-fold coordination. This bulk form of zirconia has little application due to its asymmetry. Therefore dopants are added to the grain in-order to induce phase transitions to either a tetragonal or cubic polymorph with the incorporation of oxygen vacancies due to the dopant charge mis-match with the zirconia matrix. The cubic polymorph has cubic symmetry such that these samples see applications in solid oxide fuel cells (SOFCs) due to the high oxygen vacancy concentrations and high ionic mobility at elevated temperatures. The tetragonal polymorph has slight asymmetry in the c-axis compared to the a-axis such that the tetragonal samples have increased fracture toughness due to an impact induced phase transformation to a cubic structure. These ceramic systems have been extensively studied in academia and used in various industries, but with the advent of nanotechnology one can wonder whether smaller grain samples will see improved characteristics similar to their bulk grain counterparts. However, there is a lack of data and knowledge of these systems in the nano grained region which provides us with an opportunity to advance the theory in these systems. The polymorphism seen in the bulk grains samples is also seen in the nano-grained samples, but at slightly distinct dopant concentrations. The current theory hypothesizes that a surface excess, gamma (J/m 2), can be added to the Gibbs Free energy equation to account for the additional free energy of the nano-grain atoms. However, these surface energies have been difficult to measure and therefore thermodynamic data on these nano-grained samples have been sparse. Therefore, in this work, I will use a well established water adsorption microcalorimetry apparatus to measure the water coverage isotherms

  13. Atomic structures and oxygen dynamics of CeO2 grain boundaries

    NASA Astrophysics Data System (ADS)

    Feng, Bin; Sugiyama, Issei; Hojo, Hajime; Ohta, Hiromichi; Shibata, Naoya; Ikuhara, Yuichi

    2016-02-01

    Material performance is significantly governed by grain boundaries (GBs), a typical crystal defects inside, which often exhibit unique properties due to the structural and chemical inhomogeneity. Here, it is reported direct atomic scale evidence that oxygen vacancies formed in the GBs can modify the local surface oxygen dynamics in CeO2, a key material for fuel cells. The atomic structures and oxygen vacancy concentrations in individual GBs are obtained by electron microscopy and theoretical calculations at atomic scale. Meanwhile, local GB oxygen reduction reactivity is measured by electrochemical strain microscopy. By combining these techniques, it is demonstrated that the GB electrochemical activities are affected by the oxygen vacancy concentrations, which is, on the other hand, determined by the local structural distortions at the GB core region. These results provide critical understanding of GB properties down to atomic scale, and new perspectives on the development strategies of high performance electrochemical devices for solid oxide fuel cells.

  14. Enhanced spectral emissivity of CeO2 coating with cauliflower-like microstructure

    NASA Astrophysics Data System (ADS)

    Huang, Jianping; Li, Yibin; He, Xiaodong; Song, Guangping; Fan, Chenglei; Sun, Yue; Fei, Weidong; Du, Shanyi

    2012-10-01

    Cerium dioxide is a transparent oxide with high refractive index (from 1.6 to 2.5 at 633 nm) in the visible and near-IR spectral regions. However, little attention has been paid to its optical property in mid-IR (2.5-25 μm). Here we report that the cauliflower-like microstructured CeO2 coating deposited by electron beam physical vapor deposition technique shows high emissivity up to 0.9 at 873 K in the mid-IR spectral region. The high emissivity is attributed to the coupling between free propagating waves and space-variant polarizations caused by the cauliflower-like microstructure. This high emissivity coating shows a potential application in high temperature components.

  15. Electrode engineering for improving resistive switching performance in single crystalline CeO2 thin films

    NASA Astrophysics Data System (ADS)

    Liao, Zhaoliang; Gao, Peng; Meng, Yang; Fu, Wangyang; Bai, Xuedong; Zhao, Hongwu; Chen, Dongmin

    2012-06-01

    We have studied the electrode effect on the resistive switching behavior in the single crystalline films of CeO2 grown on Nb-SrTiO3. The fabricated devices with the top electrode made of non-reactive metals (Ag, Au, Pt) show bipolar resistive switching but are volatile. In contrast, the devices with top electrodes made of reactive metals (Al, Ta, Ti) present different bipolar resistive switching direction and are non-volatile, with Ta one having the best in OFF/ON switching ratio. The devices with these kinds of electrodes also exhibit remarkably different rectification behavior because of the difference of electrode/CeO2 interface formation. These results demonstrate that it is possible to improve the performance of resistive switching by electrode engineering.

  16. Atomic structures and oxygen dynamics of CeO2 grain boundaries

    PubMed Central

    Feng, Bin; Sugiyama, Issei; Hojo, Hajime; Ohta, Hiromichi; Shibata, Naoya; Ikuhara, Yuichi

    2016-01-01

    Material performance is significantly governed by grain boundaries (GBs), a typical crystal defects inside, which often exhibit unique properties due to the structural and chemical inhomogeneity. Here, it is reported direct atomic scale evidence that oxygen vacancies formed in the GBs can modify the local surface oxygen dynamics in CeO2, a key material for fuel cells. The atomic structures and oxygen vacancy concentrations in individual GBs are obtained by electron microscopy and theoretical calculations at atomic scale. Meanwhile, local GB oxygen reduction reactivity is measured by electrochemical strain microscopy. By combining these techniques, it is demonstrated that the GB electrochemical activities are affected by the oxygen vacancy concentrations, which is, on the other hand, determined by the local structural distortions at the GB core region. These results provide critical understanding of GB properties down to atomic scale, and new perspectives on the development strategies of high performance electrochemical devices for solid oxide fuel cells. PMID:26838958

  17. High electrostrictive strain induced by defect dipoles in acceptor-doped (K0.5Na0.5)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Dai, Ye-Jing; Zhao, Yong-Jie; Zhao, Zhe; Zhao, Zhi-Hao; Zhou, Qi-Wu; Zhang, Xiao-Wen

    2016-07-01

    Acceptor doping is an efficient method to improve ferroelectric material performance through the formation of defect dipoles. Here, a high electrostrictive strain of 0.16-0.19%, and large d33\\ast of  >300 pm V-1 are obtained in CuO-doped (K0.5Na0.5)NbO3 ceramics. We analyzed the orientation relationship and the interaction between defect dipole polarization (P d) along <0 0 1> orientation and spontaneous polarization (P s) parallel to <1 1 0> in orthorhombic (K0.5Na0.5)NbO3. Thus, a ‘coupling effect’ mechanism was suggested to explain how the P d and P s can work together to contribute to the electrostrictive strains in this lead-free piezoelectric ceramic.

  18. Dielectric, Ferroelectric, and Piezoelectric Properties of Mn-Doped K0.5Na0.5NbO3 Lead-Free Ceramics

    NASA Astrophysics Data System (ADS)

    Lopez-Juarez, Rigoberto; Gomez-Vidales, Virginia; Cruz, M. P.; Villafuerte-Castrejon, M. E.

    2015-08-01

    In this work, study of manganese-doped potassium-sodium niobate ceramics was performed. It was found that, with increasing Mn2+ content from 1 mol.% to 1.5 mol.%, the Q m changed from 60 to near 500 with no appreciable detriment in piezoelectric properties. These properties first increased with 0.5 mol.%, and remained almost constant with 1 mol.% of manganese. Maximum values for d 33, d 31, and k p were 120 pC N-1, 33 pC N-1, and 36%, respectively. Thus, manganese-doped K0.5Na0.5NbO3 ceramics represent an option for high-power applications.

  19. Characterization and comparison of 1% at Yb-doped Lu2O3 and Sc2O3 ceramics as laser gain media

    NASA Astrophysics Data System (ADS)

    Pirri, A.; Toci, G.; Vannini, M.

    2012-12-01

    We present the first laser oscillation achieved on Yb-doped Sc2O3 and Lu2O3 ceramics with a level of doping as low as 1 at %, under quasi-continuous wave pumping at 968 nm. Ceramic samples reached comparable performances in terms of tunability ranges, which exceeds 41 nm, and laser output powers. In particular, with the former sample emitting at 1040.5 nm we measured a maximum output power of 2.2 W with a corresponding slope efficiency of η = 59%. The latter medium delivered 1.8 W with a slope of η = 45% at 1032.5 nm while at 1078 nm we measured 1.5 W with η = 34%. Finally, we report the measured level of the Amplified Spontaneous Emission (ASE) for both samples, which was found to be less than 0.1 mW at the maximum pump power.

  20. Random lasing in Eu³⁺ doped borate glass-ceramic embedded with Ag nanoparticles under direct three-photon excitation.

    PubMed

    Xu, Xuhui; Zhang, Wenfei; Jin, Limin; Qiu, Jianbei; Yu, Siu Fung

    2015-10-21

    We report the observation of random lasing from Eu(3+) doped borate glass ceramic films embedded with Ag nanoparticles through three-photon absorption at room temperature. Under 1179 nm ultrashort femtosecond pulse excitation, discrete sharp peaks with linewidth ∼0.4 nm emerge randomly from a broad emission band with peak wavelength at ∼612 nm. In addition, the number of sharp peaks increases with the increase of excitation power. We also show that the emission spectrum varies with different observation angles and the corresponding lasing threshold is dependent on the excitation area. Hence, we verify unambiguously that the Eu(3+) doped borate glass ceramic film supports random lasing action via three-photon absorption excitation. In addition, Ag nanoparticles, which act as light scatterers, allow the formation of random microcavities inside the bulk film.

  1. Energetics of mixing in ThO 2-CeO 2 fluorite solid solutions

    NASA Astrophysics Data System (ADS)

    Shvareva, Tatiana Y.; Alexandrov, Vitaly; Asta, Mark; Navrotsky, Alexandra

    2011-12-01

    Mixing enthalpies (Δ Hmix) of ThO 2-CeO 2 solid solutions with respect to cubic fluorite ThO 2 and CeO 2 have been measured by high temperature oxide melt solution calorimetry. The system shows a slightly positive mixing enthalpy, with a maximum value of Δ Hmix = 3.7 ± 2.5 kJ/mol at 50% Ce/(Ce + Th). Based on the regular-solution model, with an interaction parameter of 15.1 ± 2.2 kJ/mol fit to the measured data, the phase diagram is predicted to feature a miscibility gap with a calculated critical temperature of 908 ± 132 K. The results are complemented by density-functional-theory and Monte-Carlo calculations, which provide positive mixing enthalpies and a miscibility-gap phase diagram, in qualitative agreement with calorimetric results. The calculations suggest small effects of short-range order (clustering) on the mixing enthalpy above the miscibility gap. The calculated values of Δ Hmix are within the error bars of the measured values, but consistently smaller in magnitude. An analysis of the calculated results indicates that the dominant contribution to the mixing enthalpy arises from the elastic energy associated with cation size mismatch, allowing predictions of the behavior in ThO 2-UO 2 and ThO 2-PuO 2 systems. The analysis also suggests that the slightly smaller values of the computed Δ Hmix relative to experiment can be attributed to an underestimation of the magnitude of the elastic moduli in the calculations.

  2. Preparation and Characterization of Niobium Doped Lead-Telluride Glass Ceramics

    SciTech Connect

    Sathish, M.; Eraiah, B.; Anavekar, R. V.

    2011-07-15

    Niobium-lead-telluride glass ceramics of composition xNb{sub 2}O{sub 5}-(20-x) pbO-80TeO{sub 2}(where x = 0.1 mol% to 0.5 mol%) were prepared by using conventional melt quenching method. The prepared glass samples were initially amorphous in nature after annealed at 400 deg. c all samples were crystallized. This was confined by X-ray diffraction and scanning electron microscopy. The particle size of these glass ceramics have been calculated by using Debye-Scherer formula and the particle size is in the order of 15 nm to 60 nm. The scanning electron microscopy (SEM) photograph shows the presence of needle-like crystals in these samples.

  3. Lead-free BFN ceramics doped by chromium, lithium or manganese

    NASA Astrophysics Data System (ADS)

    Bochenek, Dariusz; Niemiec, Przemysław; Adamczyk, Małgorzata

    2015-10-01

    The material of the study was lead-free BaFe0.5Nb0.5O3 ceramics subject to modification. The base composition BaFe0.5Nb0.5O3 as well as the chromium, lithium and manganese modified ones were obtained using conventional mixed oxides and carbonates method. Synthesis was performed by the powder calcination method at high temperature 1250 °C for 4 h, while the densification was carried out by free sintering method under conditions 1350 °C/4 h. The paper presents a complex study of admixtures influence on the crystal structure, microstructure and dielectric properties of the BFN type samples. The mentioned dopants chromium, lithium or manganese in the BFN-type ceramics among other caused the reduction of the electric permittivity maximum as well as significant decrease in value of dielectric loss.

  4. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics

    PubMed Central

    Li, Jinglei; Li, Fei; Li, Chao; Yang, Guang; Xu, Zhuo; Zhang, Shujun

    2015-01-01

    The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I–V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I–V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I–V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I–V behavior of (Nb + In) co-doped TiO2 ceramics. PMID:25656713

  5. Colossal dielectric permittivity in (Al + Nb) co-doped rutile SnO2 ceramics with low loss at room temperature

    NASA Astrophysics Data System (ADS)

    Song, Yongli; Wang, Xianjie; Zhang, Xingquan; Qi, Xudong; Liu, Zhiguo; Zhang, Lingli; Zhang, Yu; Wang, Yang; Sui, Yu; Song, Bo

    2016-10-01

    The exploration of colossal dielectric permittivity (CP) materials with low dielectric loss in a wide range of frequencies/temperatures continues to attract considerable interest. In this paper, we report CP in (Al + Nb) co-doped rutile SnO2 ceramics with a low dielectric loss at room temperature. Al0.02Nb0.05Sn0.93O2 and Al0.03Nb0.05Sn0.92O2 ceramics exhibit high relative dielectric permittivities (above 103) and low dielectric losses (0.015 < tan δ < 0.1) in a wide range of frequencies and at temperatures from 140 to 400 K. Al doping can effectively modulate the dielectric behavior by increasing the grain and grain boundary resistances. The large differences in the resistance and conductive activation energy of the grains and grain boundaries suggest that the CP in co-doped SnO2 ceramics can be attributed to the internal barrier layer capacitor effect.

  6. Bulk and Interface Thermodynamics of Calcia-, and Yttria-doped Zirconia Ceramics: Nanograined Phase Stability

    NASA Astrophysics Data System (ADS)

    Drazin, John Walter

    Calcia-, and yttria- doped zirconia powders and samples are essential systems in academia and industry due to their observed bulk polymorphism. Pure zirconia manifests as Baddeleyite, a monoclinic structured mineral with 7-fold coordination. This bulk form of zirconia has little application due to its asymmetry. Therefore dopants are added to the grain in-order to induce phase transitions to either a tetragonal or cubic polymorph with the incorporation of oxygen vacancies due to the dopant charge mis-match with the zirconia matrix. The cubic polymorph has cubic symmetry such that these samples see applications in solid oxide fuel cells (SOFCs) due to the high oxygen vacancy concentrations and high ionic mobility at elevated temperatures. The tetragonal polymorph has slight asymmetry in the c-axis compared to the a-axis such that the tetragonal samples have increased fracture toughness due to an impact induced phase transformation to a cubic structure. These ceramic systems have been extensively studied in academia and used in various industries, but with the advent of nanotechnology one can wonder whether smaller grain samples will see improved characteristics similar to their bulk grain counterparts. However, there is a lack of data and knowledge of these systems in the nano grained region which provides us with an opportunity to advance the theory in these systems. The polymorphism seen in the bulk grains samples is also seen in the nano-grained samples, but at slightly distinct dopant concentrations. The current theory hypothesizes that a surface excess, gamma (J/m 2), can be added to the Gibbs Free energy equation to account for the additional free energy of the nano-grain atoms. However, these surface energies have been difficult to measure and therefore thermodynamic data on these nano-grained samples have been sparse. Therefore, in this work, I will use a well established water adsorption microcalorimetry apparatus to measure the water coverage isotherms

  7. High Thermal Stability of La2O3- and CeO2-Stabilized Tetragonal ZrO2.

    PubMed

    Wang, Shichao; Xie, Hong; Lin, Yuyuan; Poeppelmeier, Kenneth R; Li, Tao; Winans, Randall E; Cui, Yanran; Ribeiro, Fabio H; Canlas, Christian P; Elam, Jeffrey W; Zhang, Hongbo; Marshall, Christopher L

    2016-03-01

    Catalyst support materials of tetragonal ZrO2, stabilized by either La2O3 (La2O3-ZrO2) or CeO2 (CeO2-ZrO2), were synthesized under hydrothermal conditions at 200 °C with NH4OH or tetramethylammonium hydroxide as the mineralizer. From in situ synchrotron powder X-ray diffraction and small-angle X-ray scattering measurements, the calcined La2O3-ZrO2 and CeO2-ZrO2 supports were nonporous nanocrystallites that exhibited rectangular shapes with a thermal stability of up to 1000 °C in air. These supports had an average size of ∼ 10 nm and a surface area of 59-97 m(2)/g. The catalysts Pt/La2O3-ZrO2 and Pt/CeO2-ZrO2 were prepared by using atomic layer deposition with varying Pt loadings from 6.3 to 12.4 wt %. Monodispersed Pt nanoparticles of ∼ 3 nm were obtained for these catalysts. The incorporation of La2O3 and CeO2 into the t-ZrO2 structure did not affect the nature of the active sites for the Pt/ZrO2 catalysts for the water-gas shift reaction.

  8. Facile electrochemical synthesis of CeO2@Ag@CdS nanotube arrays with enhanced photoelectrochemical water splitting performance.

    PubMed

    Zhao, Mi; Li, Haohua; Shen, Xiaoping; Ji, Zhenyuan; Xu, Keqiang

    2015-12-14

    In this work, for the first time, three-component CeO2@Ag@CdS heterostructured nanotube arrays with remarkable photoelectrochemical (PEC) performance have been synthesized by an electrodeposition method. In this configuration, the modification with Ag nanoparticles can significantly strengthen light absorption and provide an interior direct pathway to facilitate the separation and transport of photogenerated carriers. Therefore, the CeO2@Ag@CdS heterostructured nanotubes generate a remarkable photocurrent density of 2.14 mA cm(-2) at a potential of -0.2 V (vs. Ag/AgCl), which is 9.8 and 2.4 times higher than that of the two-component CeO2@Ag system (0.218 mA cm(-2)) and the CeO2@CdS system (0.879 mA cm(-2)), respectively. It also gives efficiency as high as 69% around 360 nm in the incident photon to electron conversion efficiency (IPCE) spectrum. Moreover, the stability of the photoelectrode was tested over 16 min. Furthermore, these results provide a valuable insight for the further development of such materials for PEC water splitting.

  9. The interaction of carbon monoxide with rhodium on potassium-modified CeO2(111)

    NASA Astrophysics Data System (ADS)

    Mullins, David R.

    2016-10-01

    The adsorption and reactions of CO adsorbed on Rh particles deposited on K-covered CeO2(111) were studied by temperature programmed desorption and photoelectron spectroscopy. K deposited on CeO2(111) forms a KOX over-layer by extracting O from the ceria and partially reducing some of the Ce4 + to Ce3 +. CO does not adsorb on the KOX/ CeO2 - X(111) surface in the absence of Rh particles. CO adsorbed on Rh/K/CeO2(111) adsorbs molecularly on the Rh at 200 K. As the surface is heated the CO spills-over and reacts with the KOX to form carbonate. The carbonate decomposes at elevated temperature to produce CO and CO2. The carbonate stabilizes the KOX so that K desorbs at a higher temperature than it would in the absence of CO. When the Rh and K deposition are reversed so that K is deposited on both the Rh and the CeO2(111), CO adsorbs as CO2- at 200 K. The CO2- decomposes below 350 K to produce gas phase CO and adsorbed CO32 - and CO. The CO is stabilized by the K on the Rh and desorbs above 540 K. The carbonate decomposes into gas phase CO and CO2.

  10. High thermal stability of La2O3 and CeO2-stabilized tetragonal ZrO2

    DOE PAGESBeta

    Wang, Shichao; Xie, Hong; Lin, Yuyuan; Poeppelmeier, Kenneth R.; Li, Tao; Winans, Randall E.; Cui, Yanran; Ribeiro, Fabio H.; Canlas, Christian P.; Elam, Jeffrey W.; et al

    2016-02-15

    Catalyst support materials of tetragonal ZrO2, stabilized by either La2O3 (La2O3-ZrO2) or CeO2 (CeO2-ZrO2), were synthesized under hydrothermal conditions at 200 °C with NH4OH or tetramethylammonium hydroxide as the mineralizer. From In Situ synchrotron powder X-ray diffraction and small-angle X-ray scattering measurements, the calcined La2O3-ZrO2 and CeO2-ZrO2 supports were nonporous nanocrystallites that exhibited rectangular shapes with thermal stability up to 1000 °C in air. These supports had an average size of ~10 nm and a surface area of 59-97 m2/g. The catalysts Pt/La2O3-ZrO2 and Pt/CeO2-ZrO2 were prepared by using atomic layer deposition with varying Pt loadings from 6.3-12.4 wt %.more » Mono-dispersed Pt nanoparticles of ~3 nm were obtained for these catalysts. As a result, the incorporation of La2O3 and CeO2 into the t-ZrO2 structure did not affect the nature of the active sites for the Pt/ZrO2 catalysts for the water-gas-shift (WGS) reaction.« less

  11. An electrochemical DNA biosensor for evaluating the effect of mix anion in cellular fluid on the antioxidant activity of CeO2 nanoparticles.

    PubMed

    Zhai, Yanwu; Zhang, Yan; Qin, Fei; Yao, Xin

    2015-08-15

    CeO2 nanoparticles are of particular interest as a novel antioxidant for scavenging free radicals. However, some studies showed that they could cause cell damage or death by generating reactive oxygen species (ROS). Up to now, it is not well understood about these paradoxical phenomena. Therefore, many attentions have been paid to the factors that could affect the antioxidant activity of CeO2 nanoparticles. CeO2 nanoparticles would inevitably encounter body fluid environment for its potential medical application. In this work the antioxidant activity behavior of CeO2 nanoparticles is studied in simulated cellular fluid, which contains main body anions (HPO4(2-), HCO3(-), Cl(-) and SO4(2-)), by a method of electrochemical DNA biosensor. We found that in the solution of Cl(-) and SO4(2-), CeO2 nanoparticles can protect DNA from damage by hydroxyl radicals, while in the presence of HPO4(2-) and HCO3(-), CeO2 nanoparticles lose the antioxidant activity. This can be explained by the cerium phosphate and cerium carbonate formed on the surface of the nanoparticles, which interfere with the redox cycling between Ce(3+) and Ce(4+). These results not only add basic knowledge to the antioxidant activity of CeO2 nanoparticles under different situations, but also pave the way for practical applications of nanoceria. Moreover, it also shows electrochemical DNA biosensor is an effective method to explore the antioxidant activity of CeO2 nanoparticles.

  12. Silver nanoparticles supported on CeO2-SBA-15 by microwave irradiation possess metal-support interactions and enhanced catalytic activity.

    PubMed

    Qian, Xufang; Kuwahara, Yasutaka; Mori, Kohsuke; Yamashita, Hiromi

    2014-11-24

    Metal-support interactions (MSIs) and particle size play important roles in catalytic reactions. For the first time, silver nanoparticles supported on CeO2-SBA-15 supports are reported that possess tunable particle size and MSIs, as prepared by microwave (MW) irradiation, owing to strong charge polarization of CeO2 clusters (i.e., MW absorption). Characterizations, including TEM, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure, were carried out to disclose the influence of CeO2 contents on the Ag particle size, MSI effect between Ag nanoparticles and CeO2-SBA-15 supports, and the strong MW absorption of CeO2 clusters that contribute to the MSIs during Ag deposition. The Ag particle sizes were controllably tuned from 1.9 to 3.9 nm by changing the loading amounts of CeO2 from 0.5 to 2.0 wt%. The Ag nanoparticle size was predominantly responsible for the high turnover frequency (TOF) of 0.41 min(-1) in ammonia borane dehydrogenation, whereas both particle size and MSIs contributed to the high TOF of 555 min(-1) in 4-nitrophenol reduction for Ag/0.5CeO2-SBA-15, which were twice as large as those of Ag/SBA-15 without CeO2 and Ag/CeO2-SBA-15 prepared by conventional oil-bath heating.

  13. Direct synthesis of dimethyl carbonate from methanol and carbon dioxide over CeO2(X)-ZnO(1-X) nano-catalysts.

    PubMed

    Kang, Ki Hyuk; Joe, Wangrae; Lee, Chang Hoon; Kim, Mieock; Kim, Dong Baek; Jang, Boknam; Song, In Kyu

    2013-12-01

    CeO2(X)-ZnO(1-X) (X = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) nano-catalysts were prepared by a co-precipitation method with a variation of CeO2 content (X, mol%), and they were applied to the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Successful formation of CeO2(X)-ZnO(1-X) nano-catalysts was well confirmed by XRD analysis. The amount of DMC produced over CeO2(X)-ZnO(1-X) catalysts exhibited a volcano-shaped curve with respect to CeO2 content. Acidity and basicity of CeO2(X)-ZnO(1-X) nano-catalysts were measured by NH3-TPD and CO2-TPD experiments, respectively, to elucidate the effect of acidity and basicity on the catalytic performance in the reaction. It was revealed that the catalytic performance of CeO2(X)-ZnO(1-X) nano-catalysts was closely related to the acidity and basicity of the catalysts. Amount of dimethyl carbonate increased with increasing both acidity and basicity of the catalysts. Among the catalysts tested, CeO2(0.7)-ZnO(0.3) with the largest acidity and basicity showed the best catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. PMID:24266202

  14. Silver nanoparticles supported on CeO2-SBA-15 by microwave irradiation possess metal-support interactions and enhanced catalytic activity.

    PubMed

    Qian, Xufang; Kuwahara, Yasutaka; Mori, Kohsuke; Yamashita, Hiromi

    2014-11-24

    Metal-support interactions (MSIs) and particle size play important roles in catalytic reactions. For the first time, silver nanoparticles supported on CeO2-SBA-15 supports are reported that possess tunable particle size and MSIs, as prepared by microwave (MW) irradiation, owing to strong charge polarization of CeO2 clusters (i.e., MW absorption). Characterizations, including TEM, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure, were carried out to disclose the influence of CeO2 contents on the Ag particle size, MSI effect between Ag nanoparticles and CeO2-SBA-15 supports, and the strong MW absorption of CeO2 clusters that contribute to the MSIs during Ag deposition. The Ag particle sizes were controllably tuned from 1.9 to 3.9 nm by changing the loading amounts of CeO2 from 0.5 to 2.0 wt%. The Ag nanoparticle size was predominantly responsible for the high turnover frequency (TOF) of 0.41 min(-1) in ammonia borane dehydrogenation, whereas both particle size and MSIs contributed to the high TOF of 555 min(-1) in 4-nitrophenol reduction for Ag/0.5CeO2-SBA-15, which were twice as large as those of Ag/SBA-15 without CeO2 and Ag/CeO2-SBA-15 prepared by conventional oil-bath heating. PMID:25336086

  15. Direct synthesis of dimethyl carbonate from methanol and carbon dioxide over CeO2(X)-ZnO(1-X) nano-catalysts.

    PubMed

    Kang, Ki Hyuk; Joe, Wangrae; Lee, Chang Hoon; Kim, Mieock; Kim, Dong Baek; Jang, Boknam; Song, In Kyu

    2013-12-01

    CeO2(X)-ZnO(1-X) (X = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) nano-catalysts were prepared by a co-precipitation method with a variation of CeO2 content (X, mol%), and they were applied to the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Successful formation of CeO2(X)-ZnO(1-X) nano-catalysts was well confirmed by XRD analysis. The amount of DMC produced over CeO2(X)-ZnO(1-X) catalysts exhibited a volcano-shaped curve with respect to CeO2 content. Acidity and basicity of CeO2(X)-ZnO(1-X) nano-catalysts were measured by NH3-TPD and CO2-TPD experiments, respectively, to elucidate the effect of acidity and basicity on the catalytic performance in the reaction. It was revealed that the catalytic performance of CeO2(X)-ZnO(1-X) nano-catalysts was closely related to the acidity and basicity of the catalysts. Amount of dimethyl carbonate increased with increasing both acidity and basicity of the catalysts. Among the catalysts tested, CeO2(0.7)-ZnO(0.3) with the largest acidity and basicity showed the best catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide.

  16. Biochemical effects of six TiO2 and four CeO2 nanomaterials in HepG2 cells

    EPA Science Inventory

    Biochemical effects of six TiO2 and four CeO2 nanomaterials in HepG2 cellsBecause of their growing number of uses, nanoparticles composed of CeO2 (cosmetics, polishing materials and automotive fuel additives) and TiO2 (pigments, sunscreens and photocatalysts) are of particular to...

  17. The Effect of CeO2 Addition on the Microstructure and Properties of Ni-Based Flame-Spray Coatings

    NASA Astrophysics Data System (ADS)

    Zhang, Zhenyu; Liang, Bunv; Guo, Hongjian

    2014-04-01

    Ni-based alloy with different amount of CeO2 powders were flame sprayed and melted onto 1045 carbon steel substrate. Microstructure and properties of the coatings were studied by XRD, field emission gun scanning electron microscope (FEGSEM) and SEM analyses. The wear behavior of the coatings was investigated under dry sliding wear conditions, and was compared with that of the coatings without CeO2, The results show that the microstructure of the coating with CeO2 differs widely from the coating without CeO2, the novel microstructure is beneficial for wear resistance. Abrasive wear tests without lubricant and analysis of the worn surfaces revealed that the Ni-based alloy coatings with the addition of 0.8% CeO2 exhibit higher wear resistance.

  18. Nanostructured oxide-based powders: investigation of the growth mode of the CeO2 clusters on the YSZ surface.

    PubMed

    Natile, Marta M; Glisenti, Antonella

    2006-02-16

    CeO(2)/YSZ nanocomposite powders, characterized by increasing Ce/Zr atomic ratio, were obtained by depositing, by wet impregnation, different amounts of CeO(2) on the yttria-stabilized zirconia (YSZ) surface. These powders were characterized by means of X-ray photoelectron spectroscopy, transmission electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Experimental results allow us to obtain interesting information concerning the growth mode, the morphology, and the dimensions of the CeO(2) clusters on the YSZ supporting surface. A 3-D growing mechanism was observed for the CeO(2) nanoparticles. With increasing Ce/Zr atomic ratio the CeO(2) clusters become more and more spherical. Moreover, XPS data also show the presence of Ce(III) and Ce(IV) ions at the interface supported/supporting oxides.

  19. Surface-structure sensitivity of CeO2 nanocrystals in photocatalysis and enhancing the reactivity with nanogold

    DOE PAGESBeta

    Lei, Wanying; Zhang, Tingting; Gu, Lin; Liu, Ping; Rodriguez, José A.; Liu, Gang; Liu, Minghua

    2015-06-19

    Structure–function correlations are a central theme in heterogeneous (photo)catalysis. In this research, using aberration-corrected scanning transmission electron microscopy (STEM), the atomic surface structures of well-defined one-dimensional (1D) CeO2 nanorods (NRs) and 3D nanocubes (NCs) are directly visualized at subangstrom resolution. CeO2 NCs predominantly expose the {100} facet, with {110} and {111} as minor cutoff facets at the respective edges and corners. Notably, the outermost surface layer of the {100} facet is nearly O-terminated. Neither surface relaxations nor reconstructions on {100} are observed, indicating unusual polarity compensation, which is primarily mediated by near-surface oxygen vacancies. The surface of CeO2 NRs ismore » highly stepped, with the enclosed {110} facet exposing Ce cations and O anions on terraces. On the basis of STEM profile-view imaging and electronic structure analysis, the photoreactivity of CeO2 nanocrystals toward aqueous methyl orange degradation under UV is revealed to be surface-structure-sensitive, following the order: {110} >> {100}. The underlying surface-structure sensitivity can be attributed to the variation in low-coordinate surface cerium cations between {110} and {100} facets. To further enhance light absorption, Au nanoparticles (NPs) are deposited on CeO2 NRs to form Au/CeO2 plasmonic nanocomposites, which dramatically promotes the photoreactivity that is Au particle size- and excitation light wavelength-dependent. The mechanisms responsible for the enhancement of photocatalytic activity are discussed, highlighting the crucial role of photoexcited charge carrier transfer.« less

  20. Lattice dynamics and dielectric response of Mg-doped SrTiO3 ceramics in a wide frequency range

    NASA Astrophysics Data System (ADS)

    Tkach, A.; Vilarinho, P. M.; Kholkin, A. L.; Pashkin, A.; Samoukhina, P.; Pokorny, J.; Veljko, S.; Petzelt, J.

    2005-02-01

    Atomic substitutions in the SrTiO3 (ST) perovskite lattice are foreseen to modify the lattice vibration modes, which are apparently sensitive to the site at which the substitution occurs. In order to understand the effect of Mg substitution in the ST lattice, the dielectric properties of Sr1-xMgxTiO3 and SrTi1-yMgyO3-δ ceramics were investigated in radio frequency (rf), microwave, terahertz (THz), and infrared (IR) ranges. Micro-Raman spectroscopy and rf tunability measurements were also conducted on these samples. The micro-Raman spectra and the high-frequency dielectric properties of Sr1-xMgxTiO3, including rf tunability, do not differ considerably from the properties of undoped SrTiO3, confirming only slight (if any) incorporation of Mg into the Sr site of ST perovskite lattice. At the same time, Ti-site Mg doping results in significant stiffening of the soft lattice mode observed in IR reflectivity spectra. Dielectric permittivity and dielectric losses decrease in both rf and THz ranges accompanied by the decrease of the tunability, in accordance with the stiffened ferroelectric soft mode. The appearance in the Raman spectra of the forbidden polar modes TO4 at 545cm-1 and TO2 at 174cm-1 at room temperature and their strengthening on cooling, demonstrate the local loss of the inversion center and the breaking of the cubic symmetry by the substitution of Ti4+ by Mg2+ ions. These results confirm more favorable occupation of Mg at the Ti site of the ST lattice and show the possibility of using Ti-site Mg-doped ST as an active material for low-loss microwave waveguides and resonators.

  1. Enhance D. C. resistivity of Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} ceramic by acceptor (Mn) doping

    SciTech Connect

    Sharma, Hakikat Arya, G. S.; Pramar, Kusum; Negi, N. S.

    2015-05-15

    In the present work, we prepared Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} and Mn (2 and 3 at % on Ti site) doped Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} ceramic by sol- gel method. The samples were characterized by X-ray diffraction (XRD). The XRD patterns reveled that Mn ions did not change the perovskite structure of BST (70/30). The dielectric measurements proved that dielectric constant decreased with Mn doping. The dc resistivity was studied by using I-V measurements. The dc resistivity of the BST increased with Mn doping, which suppressed the leakage current.

  2. Room temperature magnetic and dielectric properties of cobalt doped CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

    SciTech Connect

    Mu, Chunhong; Song, Yuanqiang Wang, Xiaoning; Wang, Haibin

    2015-05-07

    CaCu{sub 3}Ti{sub 4−x}Co{sub x}O{sub 12} (x = 0, 0.2, 0.4) ceramics were prepared by a conventional solid state reaction, and the effects of cobalt doping on the room temperature magnetic and dielectric properties were investigated. Both X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the presence of Cu and Co rich phase at grain boundaries of Co-doped ceramics. Scanning electron microscopy micrographs of Co-doped samples showed a striking change from regular polyhedral particle type in pure CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) to sheet-like grains with certain growth orientation. Undoped CaCu{sub 3}Ti{sub 4}O{sub 12} is well known for its colossal dielectric constant in a broad temperature and frequency range. The dielectric constant value was slightly changed by 5 at. % and 10 at. % Co doping, whereas the second relaxation process was clearly separated in low frequency region at room temperature. A multirelaxation mechanism was proposed to be the origin of the colossal dielectric constant. In addition, the permeability spectra measurements indicated Co-doped CCTO with good magnetic properties, showing the initial permeability (μ′) as high as 5.5 and low magnetic loss (μ″ < 0.2) below 3 MHz. And the interesting ferromagnetic superexchange coupling in Co-doped CaCu{sub 3}Ti{sub 4}O{sub 12} was discussed.

  3. Enhanced ferromagnetic properties in Ho and Ni co-doped BiFeO{sub 3} ceramics

    SciTech Connect

    Park, J. S.; Yoo, Y. J.; Hwang, J. S.; Lee, Y. P.; Kang, J.-H.; Lee, B. W.

    2014-01-07

    The magnetic properties of polycrystalline Bi{sub 1-x}Ho{sub x}Fe{sub 1-y}Ni{sub y}O{sub 3} (x = 0, 0.1; y = 0, 0.03), which were prepared by the solid-state method, have been investigated. The powder X-ray diffraction reveals that all the samples are polycrystalline and show rhombohedral perovskite structure. The micro-Raman scattering studies confirm that Bi{sub 0.9}Ho{sub 0.1}Fe{sub 0.97}Ni{sub 0.03}O{sub 3} has a compressive lattice distortion induced by the simultaneous substitution of Ho and Ni ions at A and B-sites, respectively. From the magnetization dependences at room temperature, Bi{sub 0.9}Ho{sub 0.1}Fe{sub 0.97}Ni{sub 0.03}O{sub 3} has enhanced magnetization (0.2280 emu/g) and low coercive field (280 Oe). It was revealed that the Ni dopant plays an important role for the improved ferromagnetic properties and the Ho dopant favors the magnetic exchange interactions in the co-doped ceramic.

  4. Rare earth-doped lead borate glasses and transparent glass-ceramics: structure-property relationship.

    PubMed

    Pisarski, W A; Pisarska, J; Mączka, M; Lisiecki, R; Grobelny, Ł; Goryczka, T; Dominiak-Dzik, G; Ryba-Romanowski, W

    2011-08-15

    Correlation between structure and optical properties of rare earth ions in lead borate glasses and glass-ceramics was evidenced by X-ray-diffraction, Raman, FT-IR and luminescence spectroscopy. The rare earths were limited to Eu(3+) and Er(3+) ions. The observed BO(3)↔BO(4) conversion strongly depends on the relative PbO/B(2)O(3) ratios in glass composition, giving important contribution to the luminescence intensities associated to (5)D(0)-(7)F(2) and (5)D(0)-(7)F(1) transitions of Eu(3+). The near-infrared luminescence and up-conversion spectra for Er(3+) ions in lead borate glasses before and after heat treatment were measured. The more intense and narrowing luminescence lines suggest partial incorporation of Er(3+) ions into the orthorhombic PbF(2) crystalline phase, which was identified using X-ray diffraction analysis. PMID:21093353

  5. Trace element doping in calcium phosphate ceramics to Understand osteogenesis and angiogenesis

    PubMed Central

    Bose, Susmita; Fielding, Gary; Tarafder, Solaiman; Bandyopadhyay, Amit

    2013-01-01

    The general trends in synthetic bone grafting materials are shifting towards approaches that can illicit osteoinductive properties. Pharmacologics and biologics have been used in combination with calcium phosphate (CaP) ceramics, however, recently have become the target of scrutiny over the safety. The importance of trace elements in natural bone health is well documented. Ions, e.g. lithium, zinc, magnesium, manganese, silicon, strontium etc. have shown to increase osteogenesis and neovascularization. Incorporation of dopants into CaPs can provide a platform for safe and efficient delivery in clinical applications where increased bone healing is favorable. This review highlights use of trace elements in CaP biomaterials, and offers an insight into the mechanisms of how metal ions can enhance both osteogenesis and angiogenesis. PMID:24012308

  6. Fabrication and XAFS analysis of Yb3+ doped yttrium lanthanum oxide transparent ceramics

    NASA Astrophysics Data System (ADS)

    Jiang, Cen; Yang, Qiuhong; Lu, Qing; Zhang, Haojia

    2013-12-01

    (YbxY0.90-xLa0.10)2O3 (x = 0.01-0.10) transparent ceramics were fabricated and their structural properties were investigated. The XRD showed our samples exhibited single cubic Y2O3 phase. The lattice parameters were refined with the Rietveld method. The compact structure and an average grain size of 40-50 μm were revealed by the microstructure. The local fine structure around Yb ions was investigated by using the XAFS (X-ray absorption fine structure) technique. The results showed that: the local structure around Yb ions in the samples with different concentration of Yb ions was basically similar, and Yb ions replaced Y position to form the solid solution. The Yb ions were trivalent. With the concentration of Yb2O3 increased, the coordination number (N) and first shell Yb-O bond length (R) decreased, and the degree of disorder (σ) increased.

  7. Identification and inspection of the vacancy site in Li doped BPO 4 ceramic electrolyte by NMR

    NASA Astrophysics Data System (ADS)

    Dodd, A. J.; van Eck, E. R. H.

    2002-10-01

    A study of the properties of the high temperature ceramic electrolyte Li xB 1- x/3 PO 4 (lithium boron phosphate) is reported. XRD and NMR are used to investigate changes of the material as a function of heat treatment. It was found that after synthesis at 450 °C the material contains a phase of Li 4P 2O 7 in addition to the BPO 4 phase. This second phase is removed by heat treatment at temperatures higher than 600 °C. Boron vacancies are present, REDOR and CPMAS techniques are used to investigate this defect site and show that for the heat treated material Li ions are present at the vacancy site.

  8. Nucleation and crystallization of Ca doped basaltic glass for the production of a glass-ceramic material

    NASA Astrophysics Data System (ADS)

    Tarrago, Mariona; Royo, Irene; Garcia-Valles, Maite; Martínez, Salvador

    2016-04-01

    Sewage sludge from wastewater treatment plants is a waste with a composition roughly similar to that of a basalt. It may contain potentially toxic elements that can be inertized by vitrification. Using a glass-ceramic process, these elements will be emplaced in newly formed mineral phases. Glass-ceramic production requires an accurate knowledge of the temperatures of nucleation (TN) and crystal growth of the corresponding minerals. This work arises from the study of the addition of ions to a basaltic matrix in order to establish a model of vitrification of sewage sludge. In this case a glass-ceramic is obtained from a glass made with a basalt that has been doped with 16% CaO. Two glasses which underwent different cooling processes have been produced and compared. The first was annealed at 650oC (AG) and the second was quenched (QG). The chemical composition of the glasses is SiO2 36.11 wt%, Al2O312.19 wt%, CaO 24.44 wt%, FeO 10.06 wt%, MgO 9.19 wt%, Na2O 2.28 wt%, TiO2 2.02 wt%, K2O 1.12 wt%, P2O5 0.46 wt%. Glass transition temperature obtained by dilatometry varies from 640 oC (AG) to 700 oC (QG). The temperatures of nucleation and crystal growth of the glass have been determined by Differential Thermal Analysis (DTA). The phases formed after these treatments were identified by X-Ray Diffraction. The temperatures of exothermic and endothermic peaks measured in the quenched glass are, in average, 10 oC higher than those found for the annealed glass. The exothermic peaks provide crystallization temperatures for different phases: a first event at 857 oC corresponds to the growth of magnetite, pyroxene and nepheline, whereas a second event at 1030 oC is due to the crystallization of melilite from the reaction between previous minerals and a remaining amorphous phase. The complete melting of this system occurs at 1201 oC. This glass has been nucleated inside the DTA furnace (500-850° C/3 hours) and then heated up to 1300 oC using the fraction between 400-500μm. TN

  9. Novel CeO2-CuO-decorated enzymatic lactate biosensors operating in low oxygen environments.

    PubMed

    Uzunoglu, Aytekin; Stanciu, Lia A

    2016-02-25

    The detection of the lactate level in blood plays a key role in diagnosis of some pathological conditions including cardiogenic or endotoxic shocks, respiratory failure, liver disease, systemic disorders, renal failure, and tissue hypoxia. Here, we described for the first time the use of a novel mixed metal oxide solution system to address the oxygen dependence challenge of first generation amperometric lactate biosensors. The biosensors were constructed using ceria-copper oxide (CeO2-CuO) mixed metal oxide nanoparticles for lactate oxidase immobilization and as electrode material. The oxygen storage capacity (OSC, 492 μmol-O2/g) of these metal oxides has the potential to reduce the oxygen dependency, and thus eliminate false results originated from the fluctuations in the oxygen concentration. In an effort to compare the performance of our novel sensor design, ceria nanoparticle decorated lactate sensors were also constructed. The enzymatic activity of the sensors were tested in oxygen-rich and oxygen-lean solutions. Our results showed that the OSC of the electrode material has a big influence on the activity of the biosensors in oxygen-lean environments. While the CeO2 containing biosensor showed an almost 21% decrease in the sensitivity in a O2-depleted solution, the CeO2-CuO containing electrode, with a higher OSC value, experienced no drop in sensitivity when moving from oxygen-rich to oxygen-lean conditions. The CeO2-CuO decorated sensor showed a high sensitivity (89.3 ± 4 μA mM(-1) cm(-2)), a wide linear range up to 0.6 mM, and a low limit of detection of 3.3 μM. The analytical response of the CeO2-CuO decorated sensors was studied by detecting lactate in human serum with good selectivity and reliability. The results revealed that CeO2-CuO containing sensors are promising candidates for continuous lactate detection.

  10. Enhanced transport of CeO2 nanoparticles in porous media by macropores.

    PubMed

    Fang, Jing; Wang, Min-hao; Lin, Dao-hui; Shen, Bing

    2016-02-01

    This is the first study to investigate the effect of macropores on the transport of CeO2 nanoparticles (nCeO2) in quartz sand and soil. The artificial macropore types are the vertical continuous macropore (O-O), and the vertical discontinuous macropore (O-C). The results indicated that the mobility of nCeO2 was significantly enhanced by the macropore in both quartz sand and soil, and the enhancement was greater in the continuous macropore than in the discontinuous macropore. Compared with the homogeneous column, both the O-O and O-C macropores in quartz sand favored an earlier breakthrough and a larger initial effluent recovery rate of nCeO2. However, there was little influence on the plateau concentration and the total effluent recovery rate. In soil, both types of macropores significantly shortened nCeO2 breakthrough time, and favored a higher plateau concentration, and a larger initial and total effluent recovery rate. The O-O macropore which accounted for only 1% of the total pore volume had doubly increased the total mobility of nCeO2 in soil; even the mobility was increased by 30% with the O-C macropore. It was found that the effect of preferential flow on nCeO2 transport was greater in soil than it was in quartz sand. PMID:26584072

  11. High pressure and temperature equation of state and spectroscopic study of CeO2

    NASA Astrophysics Data System (ADS)

    Jacobsen, M. K.; Velisavljevic, N.; Dattelbaum, D. M.; Chellappa, R. S.; Park, C.

    2016-04-01

    One of the most widely used x-ray standards and a highly applied component of catalysis systems, CeO2 has been studied for the purpose of better understanding its equation of state and electronic properties. Diamond anvil cells have been used to extend the equation of state for this material to 130 GPa and explore the electronic behavior with applied load. From the x-ray diffraction studies, it has been determined that the high pressure phase transition extends from approximately 35-75 GPa at ambient temperature. Elevation of temperature is found to decrease the initiation pressure for this transition, with multiple distinct temperature regions which indicate structural related anomalies. In addition, hydrostatic and non-hydrostatic effects are compared and exhibit a drastic difference in bulk moduli. The electronic results indicate a change in the scattering environment of the cerium atom, associated with the high pressure phase transition. Overall, these results present the first megabar pressure study and the first high pressure and temperature study of ceria. Additionally, this shows the first combined study of the K and L III edges of this material to 33 GPa.

  12. Diffusion Barriers Block Defect Occupation on Reduced CeO2(111 )

    NASA Astrophysics Data System (ADS)

    Lustemberg, P. G.; Pan, Y.; Shaw, B.-J.; Grinter, D.; Pang, Chi; Thornton, G.; Pérez, Rubén; Ganduglia-Pirovano, M. V.; Nilius, N.

    2016-06-01

    Surface defects are believed to govern the adsorption behavior of reducible oxides. We challenge this perception on the basis of a combined scanning-tunneling-microscopy and density-functional-theory study, addressing the Au adsorption on reduced CeO2 -x(111 ) . Despite a clear thermodynamic preference for oxygen vacancies, individual Au atoms were found to bind mostly to regular surface sites. Even at an elevated temperature, aggregation at step edges and not decoration of defects turned out to be the main consequence of adatom diffusion. Our findings are explained with the polaronic nature of the Au-ceria system, which imprints a strong diabatic character onto the diffusive motion of adatoms. Diabatic barriers are generally higher than those in the adiabatic regime, especially if the hopping step couples to an electron transfer into the ad-gold. As the population of O vacancies always requires a charge exchange, defect decoration by Au atoms becomes kinetically hindered. Our study demonstrates that polaronic effects determine not only electron transport in reducible oxides but also the adsorption characteristics and therewith the surface chemistry.

  13. High pressure and temperature equation of state and spectroscopic study of CeO2.

    PubMed

    Jacobsen, M K; Velisavljevic, N; Dattelbaum, D M; Chellappa, R S; Park, C

    2016-04-20

    One of the most widely used x-ray standards and a highly applied component of catalysis systems, CeO2 has been studied for the purpose of better understanding its equation of state and electronic properties. Diamond anvil cells have been used to extend the equation of state for this material to 130 GPa and explore the electronic behavior with applied load. From the x-ray diffraction studies, it has been determined that the high pressure phase transition extends from approximately 35-75 GPa at ambient temperature. Elevation of temperature is found to decrease the initiation pressure for this transition, with multiple distinct temperature regions which indicate structural related anomalies. In addition, hydrostatic and non-hydrostatic effects are compared and exhibit a drastic difference in bulk moduli. The electronic results indicate a change in the scattering environment of the cerium atom, associated with the high pressure phase transition. Overall, these results present the first megabar pressure study and the first high pressure and temperature study of ceria. Additionally, this shows the first combined study of the K and L III edges of this material to 33 GPa. PMID:26987548

  14. Structure and surface chemistry in crystalline mesoporous (CeO(2-δ))-YSZ.

    PubMed

    Somacescu, Simona; Parvulescu, Viorica; Osiceanu, Petre; Calderon-Moreno, Jose Maria; Su, Bao-Lian

    2011-11-01

    Mesoporous metal oxides (CeO(2-δ))-YSZ have been synthesized by a versatile direct synthesis method using ionic cetyltrimethylammonium bromide (CTAB) and different nonionic (block copolymers) as surfactants and urea as hydrolyzing agent. The synthesis was realized at pH=9 using tetraethylammonium hydroxide (TEAOH) as pH mediator. Calcination at 550 °C led to the formation of crystalline metal oxides with uniform mesoporosity. The obtained materials have been characterized by thermogravimetric analysis (TG-DTG), wide and small-angle X-ray diffraction (XRD), Raman spectroscopy, Brunauer, Emmett and Teller (BET) surface area analysis, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). All the obtained materials exhibits mesoporous structure, crystalline structure indexed in a cubic symmetry, showing a high surface area, a uniform and narrow pore size distribution, spherical morphology typical for the mesoporous materials. The crystalline and mesoporous structures, surface chemistry and stoichiometry for the samples synthesized using ionic and nonionic surfactants have been discussed.

  15. Diffusion Barriers Block Defect Occupation on Reduced CeO_{2}(111).

    PubMed

    Lustemberg, P G; Pan, Y; Shaw, B-J; Grinter, D; Pang, Chi; Thornton, G; Pérez, Rubén; Ganduglia-Pirovano, M V; Nilius, N

    2016-06-10

    Surface defects are believed to govern the adsorption behavior of reducible oxides. We challenge this perception on the basis of a combined scanning-tunneling-microscopy and density-functional-theory study, addressing the Au adsorption on reduced CeO_{2-x}(111). Despite a clear thermodynamic preference for oxygen vacancies, individual Au atoms were found to bind mostly to regular surface sites. Even at an elevated temperature, aggregation at step edges and not decoration of defects turned out to be the main consequence of adatom diffusion. Our findings are explained with the polaronic nature of the Au-ceria system, which imprints a strong diabatic character onto the diffusive motion of adatoms. Diabatic barriers are generally higher than those in the adiabatic regime, especially if the hopping step couples to an electron transfer into the ad-gold. As the population of O vacancies always requires a charge exchange, defect decoration by Au atoms becomes kinetically hindered. Our study demonstrates that polaronic effects determine not only electron transport in reducible oxides but also the adsorption characteristics and therewith the surface chemistry.

  16. Thermally Stable Hierarchical Nanostructures of Ultrathin MoS2 Nanosheet-Coated CeO2 Hollow Spheres as Catalyst for Ammonia Decomposition.

    PubMed

    Gong, Xueyun; Gu, Ying-Qiu; Li, Na; Zhao, Hongyang; Jia, Chun-Jiang; Du, Yaping

    2016-04-18

    MoS2 ultrathin nanosheet-coated CeO2 hollow sphere (CeO2@MoS2) hybrid nanostructures with a 3D hierarchical configuration were successfully constructed from a facile two-step wet chemistry strategy: first, CeO2 formed on a silica core which served as a template and was subsequently removed by NaOH solution to attain hollow spheres, and then few-layered ultrathin MoS2 nanosheets were deposited on the CeO2 hollow spheres through a hydrothermal process. As a proof of concept application, the as-prepared CeO2@MoS2 hybrid nanostructures were used as catalytic material, which exhibited enhanced catalytic activity in ammonia decomposition for H2 production at high temperature. It was demonstrated that, even with a structural transformation from MoS2 to MoNx under harsh conditions of ammonia decomposition at high temperature (700 °C), the 3D hierarchical nanostructures of the CeO2@MoNx were well kept, indicating the important role of the CeO2 support.

  17. Effect of surface coating and organic matter on the uptake of CeO2 NPs by corn plants grown in soil: Insight into the uptake mechanism

    PubMed Central

    Zhao, Lijuan; Peralta-Videa, Jose R.; Varela-Ramirez, Armando; Castillo-Michel, Hiram; Li, Chunqiang; Zhang, Jianying; Aguilera, Renato J.; Keller, Arturo A.; Gardea-Torresdey, Jorge L.

    2015-01-01

    Little is known about the fate, transport, and bioavailability of CeO2 nanoparticles (NPs) in soil. Moreover, there are no reports on the effect of surface coating upon NPs uptake by plants. In this study, Zea mays plants were grown for one month in unenriched and organic soils treated with coated and uncoated CeO2 NPs. In addition, plants were exposed to fluorescein isothiocyanate (FITC)-stained CeO2 NPs and analyzed in a confocal microscope. In organic soil, roots from uncoated and coated NPs at 100, 200, 400, and 800 mg kg−1 had 40, 80, 130, and 260% and 10, 70, 90, and 40% more Ce, respectively, compared to roots from unenriched soil. Conversely, shoots of plants from unenriched soil had significantly more Ce compared with shoots from organic soil. Confocal fluorescence images showed FITC-stained CeO2 NP aggregates in cell walls of epidermis and cortex, suggesting apoplastic pathway. The μXRF results revealed the presence of CeO2 NP aggregates within vascular tissues. To the authors knowledge this is the first report on the effects of surface coating and organic matter on Ce uptake from CeO2 NPs and upon the mechanisms of CeO2 NPs uptake by higher plants PMID:22633924

  18. Citric acid modifies surface properties of commercial CeO2 nanoparticles reducing their toxicity and cerium uptake in radish (Raphanus sativus) seedlings.

    PubMed

    Trujillo-Reyes, J; Vilchis-Nestor, A R; Majumdar, S; Peralta-Videa, J R; Gardea-Torresdey, J L

    2013-12-15

    Little is known about the mobility, reactivity, and toxicity to plants of coated engineered nanoparticles (ENPs). Surface modification may change the interaction of ENPs with living organisms. This report describes surface changes in commercial CeO2 NPs coated with citric acid (CA) at molar ratios of 1:2, 1:3, 1:7, and 1:10 CeO2:CA, and their effects on radish (Raphanus sativus) seed germination, cerium and nutrients uptake. All CeO2 NPs and their absorption by radish plants were characterized by TEM, DLS, and ICP-OES. Radish seeds were germinated in pristine and CA coated CeO2 NPs suspensions at 50mg/L, 100mg/L, and 200mg/L. Deionized water and CA at 100mg/L were used as controls. Results showed ζ potential values of 21.6 mV and -56 mV for the pristine and CA coated CeO2 NPs, respectively. TEM images showed denser layers surrounding the CeO2 NPs at higher CA concentrations, as well as better distribution and smaller particle sizes. None of the treatments affected seed germination. However, at 200mg/L the CA coated NPs at 1:7 ratio produced significantly (p ≤ 0.05) more root biomass, increased water content and reduced by 94% the Ce uptake, compared to bare NPs. This suggests that CA coating decrease CeO2 NPs toxicity to plants.

  19. Nickel-doped ceria nanoparticles for promoting catalytic activity of Pt/C for ethanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Tan, Qiang; Du, Chunyu; Sun, Yongrong; Du, Lei; Yin, Geping; Gao, Yunzhi

    2014-10-01

    This paper reports the facile synthesis of monodispersed nickel-doped ceria nanoparticles by a thermal decomposition method, which is used to promote catalytic properties of Pt/C. The Pt/Ni-doped CeO2/C catalyst obtained exhibits remarkably high activity and stability towards the ethanol electrooxidation in acidic media. This is attributed to higher oxygen releasing capacity and stronger interaction of Ni-doped CeO2 with Pt than pure CeO2 nanoparticles that contribute positively to the removal of poisoning intermediates. We believe that the design concept and synthetic strategy of metal doped oxides used for fuel cell catalysts can be potentially extended to other catalytic fields.

  20. Significant enhancement in thermoelectric properties of polycrystalline Pr-doped SrTiO{sub 3−δ} ceramics originating from nonuniform distribution of Pr dopants

    SciTech Connect

    Dehkordi, Arash Mehdizadeh; Bhattacharya, Sriparna; He, Jian; Alshareef, Husam N.; Tritt, Terry M.

    2014-05-12

    Recently, we have reported a significant enhancement (>70% at 500 °C) in the thermoelectric power factor (PF) of bulk polycrystalline Pr-doped SrTiO{sub 3} ceramics employing a novel synthesis strategy which led to the highest ever reported values of PF among doped polycrystalline SrTiO{sub 3}. It was found that the formation of Pr-rich grain boundary regions gives rise to an enhancement in carrier mobility. In this Letter, we investigate the electronic and thermal transport in Sr{sub 1−x}Pr{sub x}TiO{sub 3} ceramics in order to determine the optimum doping concentration and to evaluate the overall thermoelectric performance. Simultaneous enhancement in the thermoelectric power factor and reduction in thermal conductivity in these samples resulted in more than 30% improvement in the dimensionless thermoelectric figure of merit (ZT) for the whole temperature range over all previously reported maximum values. Maximum ZT value of 0.35 was obtained at 500 °C.

  1. EPR and optical study of Yb3+-doped β-PbF2 single crystals and nanocrystals of glass-ceramics

    NASA Astrophysics Data System (ADS)

    Dantelle, G.; Mortier, M.; Goldner, Ph; Vivien, D.

    2006-08-01

    β-PbF2 single crystals doped with YbF3 (0.2% and 2%) were studied by x-ray diffraction (XRD), electron paramagnetic resonance (EPR) and optical spectroscopy. EPR revealed the presence of only one kind of paramagnetic ion Yb3+, in a cubic symmetry site. The optical absorption, emission and excitation spectra enabled us to identify the transitions attributed to Yb3+ in the cubic site and to determine its energy level diagram. Site-selective laser spectroscopy also evidenced the presence of another type of Yb3+ ions, undetectable by classical EPR. This second type, which dominates in the 2%-doped crystal and exhibits cooperative luminescence, was attributed to Yb3+ ions forming clusters. Transparent oxyfluoride glass-ceramics, containing β-Pb1-yYbyF2+y nanocrystallites, were also synthesized and studied by XRD, EPR and optical spectroscopy. Two types of Yb3+ ions were found, as in β-PbF2 single crystals. The optical properties of the oxyfluoride glass-ceramics turn out to be similar to those of ytterbium activated β-PbF2 single crystals. Moreover, the Yb environments found in PbF2 single crystals seem to already occur in the parent glass. Therefore, these materials are expected to be good laser media, like the rare-earth doped fluorite crystals, either in bulk or fibre form.

  2. A perfectly stoichiometric and flat CeO2(111) surface on a bulk-like ceria film

    PubMed Central

    Barth, C.; Laffon, C.; Olbrich, R.; Ranguis, A.; Parent, Ph.; Reichling, M.

    2016-01-01

    In surface science and model catalysis, cerium oxide (ceria) is mostly grown as an ultra-thin film on a metal substrate in the ultra-high vacuum to understand fundamental mechanisms involved in diverse surface chemistry processes. However, such ultra-thin films do not have the contribution of a bulk ceria underneath, which is currently discussed to have a high impact on in particular surface redox processes. Here, we present a fully oxidized ceria thick film (180 nm) with a perfectly stoichiometric CeO2(111) surface exhibiting exceptionally large, atomically flat terraces. The film is well-suited for ceria model studies as well as a perfect substitute for CeO2 bulk material. PMID:26879800

  3. CeO2-modified Au@SBA-15 nanocatalysts for liquid-phase selective oxidation of benzyl alcohol

    NASA Astrophysics Data System (ADS)

    Wang, Tuo; Yuan, Xiang; Li, Shuirong; Zeng, Liang; Gong, Jinlong

    2015-04-01

    Tuning the interfacial perimeter and structure is crucial to understanding the origin of catalytic performance. This paper describes the design, characterization, and application of CeO2 modified Au@SBA-15 (Au-CeO2@SBA-15) catalysts in selective oxidation of benzyl alcohol. The reaction results showed that Au-CeO2@SBA-15 catalysts exhibited higher catalytic activity compared with Au@SBA-15 and Au/CeO2 catalysts under identical conditions along with the high selectivity towards benzaldehyde (>99%). The turnover frequency of benzyl alcohol over the Au-100CeO2@SBA-15 catalyst is about nine-fold and four-fold higher than those of Au@SBA-15 and Au/CeO2 catalysts, respectively. The supported catalysts were characterized by N2 adsorption-desorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, scanning transmission electron microscopy-energy dispersive spectrometry, and X-ray photoelectron spectroscopy. It was found that the Au and small CeO2 nanoparticles (~5 nm) were homogeneously mixed in the channels of SBA-15, which led to an increase in the interfacial area between Au and CeO2 and consequently a better catalytic performance of Au-CeO2@SBA-15 catalysts for the selective oxidation of benzyl alcohol to benzaldehyde compared with that of Au/CeO2. The prevention of agglomeration and leaching of Au nanoparticles by restricting them inside the mesopores of SBA-15 was conducive to the stable existence of large quantities of Au-CeO2 interface, which leads to high stability of the Au-CeO2@SBA-15 catalyst.Tuning the interfacial perimeter and structure is crucial to understanding the origin of catalytic performance. This paper describes the design, characterization, and application of CeO2 modified Au@SBA-15 (Au-CeO2@SBA-15) catalysts in selective oxidation of benzyl alcohol. The reaction results showed that Au-CeO2@SBA-15 catalysts exhibited higher catalytic activity compared with Au@SBA-15 and Au/CeO2 catalysts under identical conditions along with the high selectivity towards benzaldehyde (>99%). The turnover frequency of benzyl alcohol over the Au-100CeO2@SBA-15 catalyst is about nine-fold and four-fold higher than those of Au@SBA-15 and Au/CeO2 catalysts, respectively. The supported catalysts were characterized by N2 adsorption-desorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, scanning transmission electron microscopy-energy dispersive spectrometry, and X-ray photoelectron spectroscopy. It was found that the Au and small CeO2 nanoparticles (~5 nm) were homogeneously mixed in the channels of SBA-15, which led to an increase in the interfacial area between Au and CeO2 and consequently a better catalytic performance of Au-CeO2@SBA-15 catalysts for the selective oxidation of benzyl alcohol to benzaldehyde compared with that of Au/CeO2. The prevention of agglomeration and leaching of Au nanoparticles by restricting them inside the mesopores of SBA-15 was conducive to the stable existence of large quantities of Au-CeO2 interface, which leads to high stability of the Au-CeO2@SBA-15 catalyst. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00246j

  4. Effect of oxidizer to fuel molar ratio on particle size and DC conductivity of CeO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Harish, B. M.; Rajeeva, M. P.; Naveen, C. S.; Chaturmukha, V. S.; Avinash, B. S.; Jayanna, H. S.; Lamani, Ashok R.

    2016-05-01

    Cerium oxide nanoparticles were synthesized by solution combustion method with varying the oxidizer (cerium nitrate hexa hydrate) to fuel (Glycine) molar ratio. The prepared samples were characterized by UV-visible spectrometer, X-ray diffractometer (XRD), Scanning electron microscope (SEM) and Energy dispersive X-Ray analysis (EDAX). XRD pattern reveals the formation of cubic fluorite structure of CeO2. It was observed that finest crystallites were found at extreme fuel-deficient condition and it is good enough to produce favorable powder characteristics. The average crystallite size was found to be 14.46 nm to 21.57 nm. The temperature dependent dc conductivity was carried out using Keithley source meter between the temperature range from 300K to 573K. From this study it was found that the conductivity increases with increase of temperature due to semiconducting behavior of CeO2 and it decreases with particle size due to increase in the energy band gap.

  5. Grain boundary defect compensation in Ti-doped BaFe0.5Nb0.5O3 ceramics

    NASA Astrophysics Data System (ADS)

    Sun, Xiaojun; Deng, Jianming; Liu, Saisai; Yan, Tianxiang; Peng, Biaolin; Jia, Wenhao; Mei, Zaoming; Su, Hongbo; Fang, Liang; Liu, Laijun

    2016-09-01

    Giant dielectric ceramics Ba(Nb0.5Fe0.5- x Ti x )O3 (BNFT) have been fabricated by a conventional solid-state reaction. According to X-ray diffraction analysis, the crystal structure of these ceramics can be described by the cubic centrosymmetric with Pm- 3m space group. The real part ( ɛ') of dielectric permittivity and dielectric loss (tan δ) of the BNFT ceramics was measured in a frequency range from 40 Hz to 100 MHz at room temperature. The ( ɛ') of all these samples displays a high value (~6500) and a small frequency-dependence from 1 kHz to 1 MHz. We have established a link between conductivity activation energy and defect compensation at grain boundaries. The Ti4+-doped Ba(Nb0.5Fe0.5)O3 as a donor makes a great influence on the grain boundary behavior, which restricts the migration of oxygen vacancy and depresses dielectric loss factor for Ba(Nb0.5Fe0.5)O3 ceramics.

  6. CeO2-modified Au@SBA-15 nanocatalysts for liquid-phase selective oxidation of benzyl alcohol.

    PubMed

    Wang, Tuo; Yuan, Xiang; Li, Shuirong; Zeng, Liang; Gong, Jinlong

    2015-05-01

    Tuning the interfacial perimeter and structure is crucial to understanding the origin of catalytic performance. This paper describes the design, characterization, and application of CeO2 modified Au@SBA-15 (Au-CeO2@SBA-15) catalysts in selective oxidation of benzyl alcohol. The reaction results showed that Au-CeO2@SBA-15 catalysts exhibited higher catalytic activity compared with Au@SBA-15 and Au/CeO2 catalysts under identical conditions along with the high selectivity towards benzaldehyde (>99%). The turnover frequency of benzyl alcohol over the Au-100CeO2@SBA-15 catalyst is about nine-fold and four-fold higher than those of Au@SBA-15 and Au/CeO2 catalysts, respectively. The supported catalysts were characterized by N2 adsorption-desorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, scanning transmission electron microscopy-energy dispersive spectrometry, and X-ray photoelectron spectroscopy. It was found that the Au and small CeO2 nanoparticles (∼5 nm) were homogeneously mixed in the channels of SBA-15, which led to an increase in the interfacial area between Au and CeO2 and consequently a better catalytic performance of Au-CeO2@SBA-15 catalysts for the selective oxidation of benzyl alcohol to benzaldehyde compared with that of Au/CeO2. The prevention of agglomeration and leaching of Au nanoparticles by restricting them inside the mesopores of SBA-15 was conducive to the stable existence of large quantities of Au-CeO2 interface, which leads to high stability of the Au-CeO2@SBA-15 catalyst.

  7. Designed Synthesis of CeO2 Nanorods and Nanowires for Studying Toxicological Effects of High Aspect Ratio Nanomaterials

    PubMed Central

    Ji, Zhaoxia; Wang, Xiang; Zhang, Haiyuan; Lin, Sijie; Meng, Huan; Sun, Bingbing; George, Saji; Xia, Tian; Nel, André E.; Zink, Jeffrey I.

    2012-01-01

    While it has been shown that high aspect ratio nanomaterials like carbon nanotubes and TiO2 nanowires can induce toxicity by acting as fiber-like substances that damage the lysosome, it is not clear what the critical lengths and aspect ratios are that induce this type of toxicity. To answer this question, we synthesized a series of cerium oxide (CeO2) nanorods and nanowires with precisely controlled lengths and aspect ratios. Both phosphate and chloride ions were shown to play critical roles in obtaining these high aspect ratio nanostructures. High resolution TEM analysis shows that single crystalline CeO2 nanorods/nanowires were formed along the [211] direction by an “oriented attachment” mechanism, followed by Ostwald ripening. The successful creation of a comprehensive CeO2 nanorod/nanowire combinatorial library allows, for the first time, the systematic study of the effect of aspect ratio on lysosomal damage, cytoxicity and IL-1β production by the human myeloid cell line (THP-1). This in vitro toxicity study demonstrated that at lengths ≥200 nm and aspect ratios ≥ 22, CeO2 nanorods induced progressive cytotoxicity and pro-inflammatory effects. The relatively low “critical” length and aspect ratio were associated with small nanorod/nanowire diameters (6–10 nm), which facilitates the formation of stacking bundles due to strong van der Waals and dipole-dipole attractions. Our results suggest that both length and diameter components of aspect ratio should be considered when addressing the cytotoxic effects of long aspect ratio materials. PMID:22564147

  8. CeO2-modified Au@SBA-15 nanocatalysts for liquid-phase selective oxidation of benzyl alcohol.

    PubMed

    Wang, Tuo; Yuan, Xiang; Li, Shuirong; Zeng, Liang; Gong, Jinlong

    2015-05-01

    Tuning the interfacial perimeter and structure is crucial to understanding the origin of catalytic performance. This paper describes the design, characterization, and application of CeO2 modified Au@SBA-15 (Au-CeO2@SBA-15) catalysts in selective oxidation of benzyl alcohol. The reaction results showed that Au-CeO2@SBA-15 catalysts exhibited higher catalytic activity compared with Au@SBA-15 and Au/CeO2 catalysts under identical conditions along with the high selectivity towards benzaldehyde (>99%). The turnover frequency of benzyl alcohol over the Au-100CeO2@SBA-15 catalyst is about nine-fold and four-fold higher than those of Au@SBA-15 and Au/CeO2 catalysts, respectively. The supported catalysts were characterized by N2 adsorption-desorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, scanning transmission electron microscopy-energy dispersive spectrometry, and X-ray photoelectron spectroscopy. It was found that the Au and small CeO2 nanoparticles (∼5 nm) were homogeneously mixed in the channels of SBA-15, which led to an increase in the interfacial area between Au and CeO2 and consequently a better catalytic performance of Au-CeO2@SBA-15 catalysts for the selective oxidation of benzyl alcohol to benzaldehyde compared with that of Au/CeO2. The prevention of agglomeration and leaching of Au nanoparticles by restricting them inside the mesopores of SBA-15 was conducive to the stable existence of large quantities of Au-CeO2 interface, which leads to high stability of the Au-CeO2@SBA-15 catalyst. PMID:25670350

  9. Good Quality Factor in GdMnO3-Doped (K0.5Na0.5)NbO3 Piezoelectric Ceramics

    NASA Astrophysics Data System (ADS)

    Bucur, Raul Alin; Badea, Iuliana; Bucur, Alexandra Ioana; Novaconi, Stefan

    2016-06-01

    (1 - x)(K0.5Na0.5)NbO3 - xGdMnO3 (KNN- xGM) ferroelectric ceramics (0 ≤ x ≤ 5 mol.%) were obtained through a solid state technique. For all the studied compositions, orthorhombic perovskite crystalline structures were obtained at room temperature. GdMnO3 suppresses the grain growth and gives rather homogenous microstructures as the concentration increases. The doped ceramics exhibita good dielectric response, a "hard" ferroelectric behavior and good piezoelectric properties. An improved mechanical quality factor of 1180 and a high Curie temperature T C = 400°C, coupled with k p = 0.426, makes the composition x = 1 mol.% GdMnO3 suitable for lead-free piezoelectric materials for high-power and high-temperature applications.

  10. Deactivation analyses of CeO2/CuO catalysts in the preferential oxidation of carbon monoxide

    NASA Astrophysics Data System (ADS)

    Zeng, Shanghong; Liu, Kewei; Zhang, Lu; Qin, Bin; Chen, Tianjia; Yin, Yueling; Su, Haiquan

    2014-09-01

    The hydrothermal in combination with impregnation methods are used to prepare the CeO2/CuO-X catalysts with spherical structure. The catalysts are characterized via SEM, XRD, H2-TPR, HRTEM, XPS and N2 adsorption-desorption techniques. The study shows that the microspheres of CuO consist of the sheet-like CuO and the way of arrangement results in the formation of shell structure. There is a core in the middle of shell structure, which is composed of the nano-sized CuO particles. CeO2 particles are supported on the surface of the CuO microspheres or embedded in the pores of sheet-like CuO. It is found that there is another reason for the decrease of CO conversion above 155 °C except H2 competitive oxidation. It is from the change of the CeO2/CuO catalyst during CO-PROX reaction including the reduction of CuO and the separation of metallic copper from the surface of catalyst.

  11. Synthesis and characterization of molybdenum catalysts supported on γ-Al2O3-CeO2 composite oxides

    NASA Astrophysics Data System (ADS)

    Farooq, Muhammad; Ramli, Anita; Subbarao, Duvvuri

    2012-09-01

    The physical and chemical properties of a catalyst play a vital role in various industrial applications. Molybdenum catalysts supported on γ-Al2O3 and γ-Al2O3-CeO2 mixed oxides with varying loading of CeO2 (5, 10, 15, 20 wt% with respect to γ-Al2O3) were prepared by wet impregnation method. The physiochemical properties of these synthesized Mo catalysts were studied with various characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), field emission scanning electron microscopy-energy dispersive analysis (FESEM-EDX) and X-ray fluorescence spectrometer (XRF). The results showed that the addition of CeO2 into the support affected the binding energies of the elements and reducibility of the metal oxides formed after calcination of catalyst samples due to the change in metal-support interaction. Further, the characterization techniques showed that the active metal was well dispersed on the surface of support material.

  12. A Molecular Approach Towards Understanding the Biogenic Formation of CeO2 and its Interactions with Biomolecules

    NASA Astrophysics Data System (ADS)

    Cervini-Silva, J.; Fakra, S.; Gilbert, B.; Banfield, J.

    2005-12-01

    Cerium is the most abundant lanthanide and generally the only one to undergo redox reactions at the Earth's surface. The oxidation state influences the environmental chemistry and toxicology of Ce because it alters the mechanisms of interaction between Ce and biomolecules. For instance, as opposed to Ce(III) or other lanthanide ions, Ce(IV) has shown a remarkable efficiency to hydrolyze DNA. The selectivity of Ce as Ce(IV) relates to the specific coordination of water molecules and their orientation. Ce(IV) may also bind selectivity to biomolecules such as RNA-type substrates, or monocleotides such as AMP, to instigate conformational changes or cleavage of complexes, which affect metabolic pathways pivotal to growth and survival. On the other hand, biogenic ligands can promote the oxidation of Ce(III) to small sized-CeO2 and are subsequently degraded by this product to CO2 and humic material. Here, we study molecular interactions between CeO2 and biomolecules (e.g., catechol) using carbon and cerium, XRD, and IR spectroscopy. Results show a progressive increase in catechol transformation (as % carbon) with decreasing CeO2 particle diameter (13 < d < 84), which substantiates an intimate relation between CeO2 unit cell expansion and reactivity towards organics susceptible to undergo redox transformations. As shown by C and Ce spectroscopy, organic polymers that form because of catechol oxidation are distributed next to the mineral surface and its occurrence is coupled to Ce reduction-oxidation.

  13. Hexahedron Prism-Anchored Octahedronal CeO2: Crystal Facet-Based Homojunction Promoting Efficient Solar Fuel Synthesis.

    PubMed

    Li, Ping; Zhou, Yong; Zhao, Zongyan; Xu, Qinfeng; Wang, Xiaoyong; Xiao, Min; Zou, Zhigang

    2015-08-01

    An unprecedented, crystal facet-based CeO2 homojunction consisting of hexahedron prism-anchored octahedron with exposed prism surface of {100} facets and octahedron surface of {111} facets was fabricated through solution-based crystallographic-oriented epitaxial growth. The photocatalysis experiment reveals that growth of the prism arm on octahedron allows to activate inert CeO2 octahedron for an increase in phototocatalytic reduction of CO2 into methane. The pronounced photocatalytic performance is attributed to a synergistic effect of the following three factors: (1) band alignment of the {100} and {111} drives electrons and holes to octahedron and prism surfaces, respectively, aiming to reach the most stable energy configuration and leading to a spatial charge separation for long duration; (2) crystallographic-oriented epitaxial growth of the CeO2 hexahedron prism arm on the octahedron verified by the interfacial lattice fringe provides convenient and fast channels for the photogenerated carrier transportation between two units of homojuntion; (3) different effective mass of electrons and holes on {100} and {111} faces leads to high charge carrier mobility, more facilitating the charge separation. The proposed facet-based homojunction in this work may provide a new concept for the efficient separation and fast transfer of photoinduced charge carriers and enhancement of the photocatalytic performance.

  14. Effect of CeO2 coupling on the structural, optical and photocatalytic properties of ZnO nanoparticle

    NASA Astrophysics Data System (ADS)

    Sherly, E. D.; Vijaya, J. Judith; Kennedy, L. John

    2015-11-01

    This research work presents the microwave assisted combustion synthesis, characterization and photocatalytic applications of ZnO-CeO2 coupled nano metal oxide. ZnO, CeO2 and the coupled oxides ZnCe, Zn2Ce and ZnCe2 with ZnO and CeO2 in the molar ratio 1:1, 2:1 and 1:2 respectively were fabricated by microwave assisted metal nitrate-urea solution combustion synthesis, without using any organic solvent or surfactant. As-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy(PL). The experiments of photocatalytic activity indicate that Zn2Ce nanoparticles exhibit excellent photocatalytic performance in the degradation of 2,4-dichlorophenol (2,4-DCP). 95% of 2,4-DCP molecules were decomposed by Zn2Ce in 240 min. The better photocatalytic degradation ability of Zn2Ce compared to ZnCe, ZnCe2 or single component ZnO and CeO2 nanoparticles is attributed to the improved separation of photogenerated electron-hole pairs.

  15. Surface degradation of CeO2 stabilized acrylic polyurethane coated thermally treated jack pine during accelerated weathering

    NASA Astrophysics Data System (ADS)

    Saha, Sudeshna; Kocaefe, Duygu; Boluk, Yaman; Pichette, Andre

    2013-07-01

    The thermally treated wood is a new value-added product and is very important for the diversification of forestry products. It drew the attention of consumers due to its attractive dark brown color. However, it loses its color when exposed to outside environment. Therefore, development of a protective coating for this value added product is necessary. In the present study, the efficiency of CeO2 nano particles alone or in combination with lignin stabilizer and/or bark extracts in acrylic polyurethane polymer was investigated by performing an accelerated weathering test. The color measurement results after accelerated weathering demonstrated that the coating containing CeO2 nano particles was the most effective whereas visual assessment suggested the coating containing CeO2 nano particles and lignin stabilizer as the most effective coating. The surface polarity changed for all the coatings during weathering and increase in contact angle after weathering suggested cross linking and reorientation of the polymer chain during weathering. The surface chemistry altered during weathering was evaluated by ATR-FTIR analysis. It suggested formation of different carbonyl byproducts during weathering. The chain scission reactions of the urethane linkages were not found to be significant during weathering.

  16. Tunability of laser based on Yb-doped hot-pressed CaF2 ceramics

    NASA Astrophysics Data System (ADS)

    Sulc, Jan; Doroshenko, Maxim E.; Jelínková, Helena; Basiev, Tasoltan T.; Konyushkin, Vasilii A.; Osiko, Vyacheslav V.

    2012-06-01

    The aim of presented study was an investigation of tunability of diode pumped laser based on hot-pressed Yb:CaF2 ceramics. The tested Yb:CaF2 sample was in the form of 3.5mm thick plane-parallel face-polished plate (without AR coatings). The Yb3+ concentration was 5.5 %. A fiber (core diameter 200 μm, NA= 0.22) coupled laser diode (LIMO, HLU25F200-980) with emission at wavelength 976 nm, was used for longitudinal Yb:CaF2 pumping. The laser diode was operating in the pulsed regime (4 ms pulse length, 20 Hz repetition rate). The duty-cycle 8% ensured a low thermal load even under the maximum diode pumping power amplitude 10W (crystal sample was only air-cooled). This radiation was focused into the crystal (pumping beam waist diameter ~ 170 μm). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.01 - 1.09 μm, HT @ 0.97 μm) and curved (r = 150mm) output coupler with a reflectivity of ~ 98% @ 1.01 - 1.09 μm. Tuning of the ytterbium laser was accomplished by using a birefringent filter (single 1.5mm thick quartz plate) placed inside the optical resonator at the Brewster angle between the output coupler and the laser active medium. The extremely broad and smooth tuning was obtained. The laser was continuously tunable over ~ 66nm (from 1015nm to 1081 nm) and the tuning band was mostly limited by free spectral range of used birefringent filter. The tunability FWHM was 40 nm corresponding bandwidth 10 THz results in Fourier limited gaussian pulse width ~ 40 fs (FWHM). The maximum output power amplitude 0.68W was obtained at wavelength 1054nm for absorbed pump power amplitude 6W. The laser slope efficiency was 15%.

  17. Lead-gallium glasses and glass-ceramics doped with SiO2 for near infrared transmittance

    NASA Astrophysics Data System (ADS)

    Marczewska, Agnieszka; Środa, Marcin; Nocuń, Marek; Sulikowski, Bogdan

    2015-07-01

    Lead-gallium glasses, due to the absence of typical glass-forming components, are characterized by an increased tendency to crystallization. Despite this, they are interesting materials due to a shift of IR absorption edge up to 6-7 μm. The paper considers how the SiO2 dopant affects thermal stability and the UV-VIS and IR transmittance of lead-gallium glasses. The base lead-gallium glass (0.75PbO·0.25Ga2O3) was modified by the addition of 5, 10 and 15 mol% SiO2, respectively. DTA/DSC data showed that the glasses are characterized by the multi-stage crystallization, which is changed with the amount of silica doped. The XRD analysis confirmed that: (i) different forms of lead oxide crystallize after heat treatment of the glass, and (ii) the Ga2PbO4 phase is formed at higher temperatures. The silica admixture allowed inserting a few percent of BaF2 into the lead-gallium glass structure. It was found that a transparent glass-ceramic based on the lead-gallium glass with a low phonon barium fluoride phase can be obtained during the thermal treatment. The study of UV-VIS-IR transmittance shows that 10-15 mol% SiO2 in the lead-gallium glasses diminishes the absorption band in the range of 2.6-4 μm due to the presence of hydroxyl groups and simultaneously reduces transmittance in the range of 5-6.5 μm from 10 to 20%. Introduction of SiO2 to the glass results in the increase of transmittance in the shorter wavelength region and the UV-edge shift is observed. It was also confirmed that the BaF2 nanocrystallites exert no effect on the transmittance of the spectrum analyzed.

  18. Functionalized PLGA-doped zirconium oxide ceramics for bone tissue regeneration.

    PubMed

    Lupu-Haber, Yael; Pinkas, Oded; Boehm, Stefanie; Scheper, Thomas; Kasper, Cornelia; Machluf, Marcelle

    2013-12-01

    Bone tissue engineering is an alternative approach to bone grafts. In our study we aim to develop a composite scaffold for bone regeneration made of doped zirconium oxide (ZrO2) conjugated with poly(lactic-co-glycolic acid) (PLGA) particles for the delivery of growth factors. In this composite, the PLGA microspheres are designed to release a crucial growth factor for bone formation, bone morphogenetic protein-2 (BMP2). We found that by changing the polymer's molecular weight and composition, we could control microsphere loading, release and size. The BMP2 released from PLGA microspheres retained its biological activity and increased osteoblastic marker expression in human mesenchymal stem cells (hMSCs). Uncapped PLGA microspheres were conjugated to ZrO2 scaffolds using carbodiimide chemistry, and the composite scaffold was shown to support hMSCs growth. We also demonstrated that human umbilical vein endothelial cells (HUVECs) can be co-cultured with hMSCs on the ZrO2 scaffold for future vascularization of the scaffold. The ZrO2 composite scaffold could serve as a bone substitute for bone grafting applications with the added ability of releasing different growth factors needed for bone regeneration.

  19. Formation mechanism and characteristics of lanthanum-doped BaTiO{sub 3} powders and ceramics prepared by the sol–gel process

    SciTech Connect

    Ianculescu, Adelina Carmen; Vasilescu, Catalina Andreea; Crisan, Maria; Raileanu, Malina; Vasile, Bogdan Stefan; Calugaru, Mihai; Crisan, Dorel; Dragan, Nicolae; Curecheriu, Lavinia; Mitoseriu, Liliana

    2015-08-15

    Pure and lanthanum-doped barium titanate nanopowders described by two different formulae, as Ba{sub 1−x}La{sub x}TiO{sub 3}, for lower La concentrations (0 ≤ x ≤ 0.005) and Ba{sub 1−x}La{sub x}Ti{sub 1−x/4}O{sub 3} for higher La concentration (x = 0.025) were prepared by an alkoxide sol–gel method. Single phase compositions were obtained after annealing at 900 °C for 2 h, in air. The increase of the lanthanum content causes structural and morphological changes in the oxide powders, including the evolution of the unit cell from tetragonal toward a cubic symmetry, the particle size decrease and a higher aggregation tendency. SEM investigations of the ceramics sintered at 1300 °C for 4 h indicate significant changes of the microstructural features (strong decrease of the average grain size and increase of the intergranular porosity) with the raise of La amount. Lanthanum addition to barium titanate prepared by sol–gel induces a more significant shift of the Curie temperature toward lower values, than that one reported in literature for ceramics of similar compositions, but processed by the conventional solid state method. The compositions with smaller La amount (x ≤ 0.005) show semiconducting properties at room temperature and high relative dielectric permittivity values, while the undoped ceramics and those doped with higher La content (x = 0.025) are good dielectrics. The ceramic with x = 0.025 exhibits acceptable low losses, a very diffuse ferroelectric–paraelectric transition and Curie temperature closed to the room temperature, being thus susceptible for high tunability applications. - Highlights: • Ba{sub 1−x}La{sub x}TiO{sub 3} (x ≤ 0.005) and Ba{sub 1−x}La{sub x}Ti{sub 1−x/4}O{sub 3} (x = 0.025) were prepared by sol–gel. • Ceramics with x < 0.5 exhibit semiconductor and high dielectric properties. • Ceramic with x = 0.025 exhibits acceptable low losses and diffuse phase transition.

  20. Rational design of octahedron and nanowire CeO2@MnO2 core-shell heterostructures with outstanding rate capability for asymmetric supercapacitors.

    PubMed

    Zhu, Shi Jin; Jia, Jia Qi; Wang, Tian; Zhao, Dong; Yang, Jian; Dong, Fan; Shang, Zheng Guo; Zhang, Yu Xin

    2015-10-14

    Two kinds of novel CeO2@MnO2 nanostructures have been synthesized via a self-assembly strategy. The as-prepared CeO2 nanowire@MnO2 nanostructures exhibited unprecedented pseudocapacitance performance (255 F g(-1)) with outstanding rate capability. A new mechanism based on the synergistic effect between CeO2 and MnO2 was proposed to interpret this phenomenon. When assembled as an asymmetric supercapacitor, an energy density of 27.5 W h kg(-1) with a maximum power density of 1.6 kW kg(-1) was achieved for CeO2 nanowire@MnO2 nanostructures.

  1. Utilizing peroxide as precursor for the synthesis of CeO2/ZnO composite oxide with enhanced photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Lv, Zijian; Zhong, Qin; Ou, Man

    2016-07-01

    A facile synthesis method of CeO2/ZnO composite oxides with higher oxygen vacancy concentration was developed by a two-step precipitation method, in which peroxide was used as precursor. The photocatalytic activity of the catalysts under UV irradiation was studied in degradation of methylene blue (MB). All CeO2/ZnO photocatalysts exhibited higher photocatalytic performance than pure ZnO, and 1%CeO2/ZnO showed highest photocatalytic activity among the prepared catalysts. It was confirmed that the synergistic effect of CeO2 and oxygen vacancy caused the improved photocatalytic activity. Furthermore, the mechanism was investigated by introducing different additives, and it was found that the hydroxyl radicals played a crucial role in degradation process.

  2. Piezoelectric properties and diffusion phase transition around PPT of La-doped (Na0.52K0.44Li0.04) Nb0.8Ta0.2O3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Yang, Wenlong; Wang, Li; Li, Haidong; Han, Junsheng; Xiu, Hanjiang; Zhou, Zhongxiang

    2016-10-01

    Lead-free ceramics (Na0.52K0.44Li0.04)1-3xLaxNb0.8Ta0.2O3 (KNLNT-Lax, x=0.00, 0.25, 0.5, 0.75, 1.00, 1.25 mol%) as non-polluting materials were prepared by solid state reaction method. The structure, piezoelectric proprieties and temperature stability of KNLNT ceramic with different La doping concentrations were investigated. The results show a transition from orthorhombic-tetragonal mix phase to tetragonal single phase with the variation of La3+ concentrations. The SEM micrographs of surface and fractured surface show a dense microstructure with few micropores. The La-doped KNLTN ceramic will be an alternative candidate contributes to excellent piezoelectric properties, which are found in the 0.75 mol% La-doped KNLNT ceramics, with d33=215pC/N, kp=42.8%and Qm=89. It has been remarkably improved that the temperature stability of KNLTN-Lax piezoelectric properties at room temperature, and the dielectric relaxation can be observed obviously. The mechanism of La doping was analyzed in terms of valence compensation and polymorphic phase transition (PPT) diffusion. The orthorhombic-tetragonal phase transition around room temperature and the relaxation transition were considered contributing to the excellent piezoelectric performance and improved temperature stability of La3+-doped KNLTN.

  3. Preparation and characterization of TiO2 and Si-doped octacalcium phosphate composite coatings on zirconia ceramics (Y-TZP) for dental implant applications

    NASA Astrophysics Data System (ADS)

    Bao, Lei; Liu, Jingxiao; Shi, Fei; Jiang, Yanyan; Liu, Guishan

    2014-01-01

    In order to prevent the low temperature degradation and improve the bioactivity of zirconia ceramic implants, TiO2 and Si-doped octacalcium phosphate composite coating was prepared on zirconia substrate. The preventive effect on low temperature degradation and surface morphology of the TiO2 layer were studied. Meanwhile, the structure and property changes of the bioactive coating after doping Si were discussed. The results indicate that the dense TiO2 layer, in spite of some microcracks, inhibited the direct contact of the water vapor with the sample's surface and thus prevented the low temperature degradation of zirconia substrates. The acceleration aging test shows that the ratio of the monoclinic phase transition decreased from 10% for the original zirconia substrate to 4% for the TiO2-coated substrate. As to the Si-doped octacalcium phosphate coating prepared by biomimetic method, the main phase composition of the coating was octacalcium phosphate. The morphology of the coating was lamellar-like, and the surface was uniform and continuous with no cracks being observed. It is suggested that Si was added into the coating both through substituting for PO43- and doping as NaSiO3.

  4. Stress response and tolerance of Zea mays to CeO2 nanoparticles: cross talk among H2O2, heat shock protein, and lipid peroxidation.

    PubMed

    Zhao, Lijuan; Peng, Bo; Hernandez-Viezcas, Jose A; Rico, Cyren; Sun, Youping; Peralta-Videa, Jose R; Tang, Xiaolei; Niu, Genhua; Jin, Lixin; Varela-Ramirez, Armando; Zhang, Jian-ying; Gardea-Torresdey, Jorge L

    2012-11-27

    The rapid development of nanotechnology will inevitably release nanoparticles (NPs) into the environment with unidentified consequences. In addition, the potential toxicity of CeO(2) NPs to plants and the possible transfer into the food chain are still unknown. Corn plants (Zea mays) were germinated and grown in soil treated with CeO(2) NPs at 400 or 800 mg/kg. Stress-related parameters, such as H(2)O(2), catalase (CAT), and ascorbate peroxidase (APX) activity, heat shock protein 70 (HSP70), lipid peroxidation, cell death, and leaf gas exchange were analyzed at 10, 15, and 20 days post-germination. Confocal laser scanning microscopy was used to image H(2)O(2) distribution in corn leaves. Results showed that the CeO(2) NP treatments increased accumulation of H(2)O(2), up to day 15, in phloem, xylem, bundle sheath cells and epidermal cells of shoots. The CAT and APX activities were also increased in the corn shoot, concomitant with the H(2)O(2) levels. Both 400 and 800 mg/kg CeO(2) NPs triggered the up-regulation of the HSP70 in roots, indicating a systemic stress response. None of the CeO(2) NPs increased the level of thiobarbituric acid reacting substances, indicating that no lipid peroxidation occurred. CeO(2) NPs, at both concentrations, did not induce ion leakage in either roots or shoots, suggesting that membrane integrity was not compromised. Leaf net photosynthetic rate, transpiration, and stomatal conductance were not affected by CeO(2) NPs. Our results suggest that the CAT, APX, and HSP70 might help the plants defend against CeO(2) NP-induced oxidative injury and survive NP exposure. PMID:23050848

  5. Er(3+)-doped transparent glass ceramics containing micron-sized SrF2 crystals for 2.7 μm emissions.

    PubMed

    Jiang, Yiguang; Fan, Jintai; Jiang, Benxue; Mao, Xiaojian; Tang, Junzhou; Xu, Yinsheng; Dai, Shixun; Zhang, Long

    2016-01-01

    Er(3+)-doped transparent glass ceramics containing micron-sized SrF2 crystals were obtained by direct liquid-phase sintering of a mixture of SrF2 powders and precursor glass powders at 820 °C for 15 min. The appearance and microstructural evolution of the SrF2 crystals in the resulting glass ceramics were investigated using X-ray diffraction, field-emission scanning electron microscopy and transmission microscopy. The SrF2 crystals are ~15 μm in size and are uniformly distributed throughout the fluorophosphate glass matrix. The glass ceramics achieve an average transmittance of 75% in the visible region and more than 85% in the near-IR region. The high transmittance of the glass ceramics results from matching the refractive index of the SrF2 with that of the precursor glass. Energy dispersive spectroscopy, photoluminescence spectra, and photoluminescence lifetimes verified the incorporation of Er(3+) into the micron-sized SrF2 crystals. Intense 2.7 μm emissions due to the (4)I11/2 → (4)I13/2 transition were observed upon excitation at 980 nm using a laser diode. The maximum value of the emission cross section of Er(3+) around 2.7 μm is more than 1.2 × 10(-20) cm(2), which indicates the potential of using transparent glass ceramics containing micron-sized SrF2 crystals for efficient 2.7 μm lasers and amplifiers. PMID:27430595

  6. Er3+-doped transparent glass ceramics containing micron-sized SrF2 crystals for 2.7 μm emissions

    NASA Astrophysics Data System (ADS)

    Jiang, Yiguang; Fan, Jintai; Jiang, Benxue; Mao, Xiaojian; Tang, Junzhou; Xu, Yinsheng; Dai, Shixun; Zhang, Long

    2016-07-01

    Er3+-doped transparent glass ceramics containing micron-sized SrF2 crystals were obtained by direct liquid-phase sintering of a mixture of SrF2 powders and precursor glass powders at 820 °C for 15 min. The appearance and microstructural evolution of the SrF2 crystals in the resulting glass ceramics were investigated using X-ray diffraction, field-emission scanning electron microscopy and transmission microscopy. The SrF2 crystals are ~15 μm in size and are uniformly distributed throughout the fluorophosphate glass matrix. The glass ceramics achieve an average transmittance of 75% in the visible region and more than 85% in the near-IR region. The high transmittance of the glass ceramics results from matching the refractive index of the SrF2 with that of the precursor glass. Energy dispersive spectroscopy, photoluminescence spectra, and photoluminescence lifetimes verified the incorporation of Er3+ into the micron-sized SrF2 crystals. Intense 2.7 μm emissions due to the 4I11/2 → 4I13/2 transition were observed upon excitation at 980 nm using a laser diode. The maximum value of the emission cross section of Er3+ around 2.7 μm is more than 1.2 × 10‑20 cm2, which indicates the potential of using transparent glass ceramics containing micron-sized SrF2 crystals for efficient 2.7 μm lasers and amplifiers.

  7. Er3+-doped transparent glass ceramics containing micron-sized SrF2 crystals for 2.7 μm emissions

    PubMed Central

    Jiang, Yiguang; Fan, Jintai; Jiang, Benxue; Mao, Xiaojian; Tang, Junzhou; Xu, Yinsheng; Dai, Shixun; Zhang, Long

    2016-01-01

    Er3+-doped transparent glass ceramics containing micron-sized SrF2 crystals were obtained by direct liquid-phase sintering of a mixture of SrF2 powders and precursor glass powders at 820 °C for 15 min. The appearance and microstructural evolution of the SrF2 crystals in the resulting glass ceramics were investigated using X-ray diffraction, field-emission scanning electron microscopy and transmission microscopy. The SrF2 crystals are ~15 μm in size and are uniformly distributed throughout the fluorophosphate glass matrix. The glass ceramics achieve an average transmittance of 75% in the visible region and more than 85% in the near-IR region. The high transmittance of the glass ceramics results from matching the refractive index of the SrF2 with that of the precursor glass. Energy dispersive spectroscopy, photoluminescence spectra, and photoluminescence lifetimes verified the incorporation of Er3+ into the micron-sized SrF2 crystals. Intense 2.7 μm emissions due to the 4I11/2 → 4I13/2 transition were observed upon excitation at 980 nm using a laser diode. The maximum value of the emission cross section of Er3+ around 2.7 μm is more than 1.2 × 10−20 cm2, which indicates the potential of using transparent glass ceramics containing micron-sized SrF2 crystals for efficient 2.7 μm lasers and amplifiers. PMID:27430595

  8. Er(3+)-doped transparent glass ceramics containing micron-sized SrF2 crystals for 2.7 μm emissions.

    PubMed

    Jiang, Yiguang; Fan, Jintai; Jiang, Benxue; Mao, Xiaojian; Tang, Junzhou; Xu, Yinsheng; Dai, Shixun; Zhang, Long

    2016-07-19

    Er(3+)-doped transparent glass ceramics containing micron-sized SrF2 crystals were obtained by direct liquid-phase sintering of a mixture of SrF2 powders and precursor glass powders at 820 °C for 15 min. The appearance and microstructural evolution of the SrF2 crystals in the resulting glass ceramics were investigated using X-ray diffraction, field-emission scanning electron microscopy and transmission microscopy. The SrF2 crystals are ~15 μm in size and are uniformly distributed throughout the fluorophosphate glass matrix. The glass ceramics achieve an average transmittance of 75% in the visible region and more than 85% in the near-IR region. The high transmittance of the glass ceramics results from matching the refractive index of the SrF2 with that of the precursor glass. Energy dispersive spectroscopy, photoluminescence spectra, and photoluminescence lifetimes verified the incorporation of Er(3+) into the micron-sized SrF2 crystals. Intense 2.7 μm emissions due to the (4)I11/2 → (4)I13/2 transition were observed upon excitation at 980 nm using a laser diode. The maximum value of the emission cross section of Er(3+) around 2.7 μm is more than 1.2 × 10(-20) cm(2), which indicates the potential of using transparent glass ceramics containing micron-sized SrF2 crystals for efficient 2.7 μm lasers and amplifiers.

  9. Microstructure and electrical properties in W/Nb co-doped Aurivillius phase Bi{sub 4}Ti{sub 3}O{sub 12} piezoelectric ceramics

    SciTech Connect

    Peng, Zhihang; Chen, Qiang; Chen, Yu; Xiao, Dingquan; Zhu, Jianguo

    2014-11-15

    Highlights: • W/Nb codoped BIT ceramics were prepared by the mixed oxides route. • High nd{sup 0} electronic configuration of W/Nb reduces the lattice distortion and T{sub C}. • Oxygen vacancy is responsible for dielectric relaxation and DC conduction process. • W/Nb additives significantly enhanced the piezoelectric coefficient d{sub 33} value. • BWNb-10 ceramics possessed large remnant polarization and a wide sintering window. - Abstract: Aurivillius-type Bi{sub 4}Ti{sub 3-x}W{sub x/2}Nb{sub x/2}O{sub 12} ceramics were prepared by a conventional solid-state sintering method. The XRD patterns demonstrated that all compositions were a single three layered crystalline structure, involving a reduction of lattice distortion with an increase in W/Nb doping level. The electrical properties including dielectric, electrical conduction and piezoelectric properties were tailored by W/Nb additives. The Curie-temperature decreased, whereas the electrical resistivity drastically increased with introduction of W/Nb donor dopants. As a result, a high electric field can be applied during the poling process. The Bi{sub 4}Ti{sub 2.9}W{sub 0.05}Nb{sub 0.05}O{sub 12} ceramics exhibited optimum piezoelectric coefficient (d{sub 33} ∼22.8 pC/N), large remnant polarization (2P{sub r} ∼26.8 μC/cm{sup 2} @ 200 °C) together with a high Curie temperature (T{sub C} ∼635 °C). Furthermore, this composition possessed a wide sintering window with outstanding piezoelectric properties. These parameters indicate that Bi{sub 4}Ti{sub 2.9}W{sub 0.05}Nb{sub 0.05}O{sub 12}-based ceramic is a promising candidate for high temperature piezoelectric applications.

  10. MOD approach for the growth of epitaxial CeO2 buffer layers on biaxially textured Ni W substrates for YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Bhuiyan, M. S.; Paranthaman, M.; Sathyamurthy, S.; Aytug, T.; Kang, S.; Lee, D. F.; Goyal, A.; Payzant, E. A.; Salama, K.

    2003-11-01

    We have grown epitaxial CeO2 buffer layers on biaxially textured Ni-W substrates for YBCO coated conductors using a newly developed metal organic decomposition (MOD) approach. Precursor solution of 0.25 M concentration was spin coated on short samples of Ni-3 at%W (Ni-W) substrates and heat-treated at 1100 °C in a gas mixture of Ar-4%H2 for 15 min. Detailed x-ray studies indicate that CeO2 films have good out-of-plane and in-plane textures with full-width-half-maximum values of 5.8° and 7.5°, respectively. High temperature in situ XRD studies show that the nucleation of CeO2 films starts at 600 °C and the growth completes within 5 min when heated at 1100 °C. SEM and AFM investigations of CeO2 films reveal a fairly dense microstructure without cracks and porosity. Highly textured YSZ barrier layers and CeO2 cap layers were deposited on MOD CeO2-buffered Ni-W substrates using rf-magnetron sputtering. Pulsed laser deposition (PLD) was used to grow YBCO films on these substrates. A critical current, Jc, of about 1.5 MA cm-2 at 77 K and self-field was obtained on YBCO (PLD)/CeO2 (sputtered)/YSZ (sputtered)/CeO2 (spin-coated)/Ni-W.

  11. Electronic storage capacity of ceria: role of peroxide in Aux supported on CeO2(111) facet and CO adsorption.

    PubMed

    Liu, Yinli; Li, Huiying; Yu, Jun; Mao, Dongsen; Lu, Guanzhong

    2015-11-01

    Density functional theory (DFT+U) was used to study the adsorption of Aux (x = 1-4) clusters on the defective CeO2(111) facet and CO adsorption on the corresponding Aux/CeO2-x catalyst, in this work Aux clusters are adsorbed onto the CeO2-x + superoxide/peroxide surface. When Au1 is supported on the CeO2(111) facet with an O vacancy, the strong electronegative Au(δ-) formed is not favorable for CO adsorption. When peroxide is adsorbed on the CeO2(111) facet with the O vacancy, Aux was oxidized, resulting in stable Aux adsorption on the defective ceria surface with peroxide, which promotes CO adsorption on the Aux/CeO2-x catalyst. With more Au atoms in supported Aux clusters, CO adsorption on this surface becomes stronger. During both the Au being supported on CeO2-x and CO being adsorbed on Aux/CeO2-x, CeO2 acts as an electron buffer that can store/release the electrons. These results provide a scientific understanding for the development of high-performance rare earth catalytic materials.

  12. Synthesis of Fe3O4/SiO2/CeO2 core-shell magnetic and their application as photocatalyst.

    PubMed

    Channei, D; Inceesungvorn, B; Wetchakun, N; Phanichphant, S

    2014-10-01

    The Fe3O4/SiO2/CeO2 core-shell magnetic has been successfully synthesized by three steps of hydrothermal, sonochemical and homogeneous precipitation by coating CeO2 nanoparticles onto Fe3O4/SiO2 magnetic core. The prepared samples were characterized by X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM) connected with energy dispersive X-ray analysis system (EDS), high resolution transmission electron microscopy (HRTEM), Nitrogen adsorption-desorption analyses (BET), and vibrating sample magnetometer (VSM). The photocatalytic activities for Fe3O4/SiO2/CeO2 core-shell magnetic under UV and visible lights were measured by determining the degradation rate of formic and oxalic acid in spiral reactor for 120 min. The amounts of CO2 generated during the process were compared between the magnetic catalyst and bare CeO2. After the finished photocatalytic degradation, the magnetic catalyst was recovered by external magnetic field at the end of each experiment. The results showed that the photocatalytic activity of Fe3O4/SiO2/CeO2 core-shell magnetic had higher than that of bare CeO2 and was found to be constant for three cycles of the recycled use.

  13. Epitaxial growth of ZnO film on Si(1 1 1) with CeO2(1 1 1) as buffer layer

    NASA Astrophysics Data System (ADS)

    Wong, T. I.; Tan, H. R.; Sentosa, D.; Wong, L. M.; Wang, S. J.; Feng, Y. P.

    2012-10-01

    ZnO(0 0 2) epitaxial films have been successfully grown on Si(1 1 1) with CeO2 as a buffer layer by pulsed laser deposition. In spite of large lattice mismatch between ZnO and CeO2, good film quality was achieved, as proven by Fourier filtered high-resolution transmission electron microscopy (HRTEM) image, due to reduction in interface strain by domain matching epitaxy. The epitaxial relationship of ZnO and CeO2 on the Si substrate was determined to be (0 0 2)[2 1 0]ZnO‖(1 1 1)[1 1 2] _CeO_2\\Vert (1 1 1)[1 1 2]Si. The HRTEM images show low defect concentrations in both the deposited ZnO film and CeO2 layer. Ordered crack lines are observed on the surface of the ZnO film which are due to A-type and B-type stackings of CeO2 on Si(1 1 1). Sharp near-band edge emission at 3.253 eV was detected for the ZnO film through photoluminiscence measurement at room temperature.

  14. Structural, dielectric, ferroelectric, and electrocaloric properties of 2% Gd2O3 doping (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Turki, O.; Slimani, A.; Seveyrat, L.; Sebald, G.; Perrin, V.; Sassi, Z.; Khemakhem, H.; Lebrun, L.

    2016-08-01

    Structural, dielectric, and ferroelectric properties, and electrocaloric effects of pure and Gd doped ( Na0.5 Bi 0.5 ) 0.94 Ba 0.06 TiO 3 ceramics prepared by the conventional solid-solid method have been carried out. The X-ray diffraction analysis confirms a pure perovskite structure with the coexistence of tetragonal and rhombohedra structures in both powders. The thermal and frequency dependences of the dielectric constants of both ceramics revealed relaxor behavior. The two compounds exhibited two phase transitions: ferroelectric/antiferroelectric (FE/AFE) transition followed by an antiferroelectric/paraelectric (AFE/PE) transition at higher temperatures. Remarkably, we noticed that the small amount of Gd doping (2%) highly enhanced the dielectric properties of the parent compound by about 71%. The phase diagram was as well influenced by the Gd doping, where the FE/AFE transition temperature rose from 90 in the parent compound to 115 °C in the doped one whereas the AFE/PE transition temperature was decreased from 320 to 270 °C, respectively. The direct electrocaloric measurements performed on both compounds showed that the ferroelectric/antiferroelectric phase transition was accompanied by a significant electrocaloric effect. The Gd3+ doping improved the electrocaloric properties of the parent compound, where a remarkable temperature variation of 1.4 K was obtained in the doped ceramic. The results of the direct electrocaloric measurements will be compared and discussed with those derived from the indirect method.

  15. The effects of physicochemical properties of CeO2 nanoparticles on toxicity to soil denitrification processes

    NASA Astrophysics Data System (ADS)

    Dahle, Jessica Teague

    The studies presented in this thesis identify the impact of NP CeO 2 on soil denitrifying microbial communities and reveal that physical and chemical characteristics including particle size, speciation, concentration, pH, and presence of ligands are key to predicting environmental fate and reactivity of NP CeO2 in the soil. A review of the literature in Chapter 1 revealed a widespread lack of toxicological information for soil exposures to NP CeO2. Soil denitrifying bacteria are a keystone species because they serve an important role in the global nitrogen cycle controlling the atmospheric nitrogen input. Soil denitrifiers are important to this study because the reducing conditions during denitrification could induce phase transformation of Ce(IV) to Ce(III), potentially influencing the toxicity of Ce. Cerium is well known for being the only lanthanide that is thermodynamically stable in both the trivalent and tetravalent state in low temperature geochemical environments. Using well characterized NP Ce(IV)O 2 as well as bulk soluble Ce(III), batch denitrification experiments were conducted to evaluate the toxicity of Ce species to the denitrifying community in a Toccoa sandy loam soil. The statistical analysis on the antimicrobial effect on soil denitrifiers was conducted using both steady-state evaluation and zero-order kinetic models in order to compare the toxicity of the Ce(III) species to the NPs. These studies, presented in Chapter 3, show that soluble Ce(III) is far more toxic than Ce(IV)O2 NPs when an equal total concentration of Ce is used, though both species exhibit toxicity to the denitrifiers via statistically significant inhibition of soil denitrification processes. Particle-size dependent toxicity, species-dependent toxicity, and concentration-dependent toxicity were all observed in this study for both the steady-state and the kinetic evaluations. The possibility of toxicity enhancement and diminishment via dissolution and ligand complexation pathways was investigated thoroughly in Chapter 2. In addition to the equilibrium and kinetic-based toxicological assessments presented in Chapter 1, dissolution and sorption experiments were performed to gain an overall understanding of Ce biogeochemistry in the terrestrial environment post-release and reveal possible geochemical controls on toxicity. It was shown that dissolution of bioavailable Ce is pH-dependent; dissolution is only detectable at acidic pH values (< pH 5) and increases with increasing acidity. Dissolution of Ce from NP CeO2 was identified to be almost 100% Ce(III). It was also demonstrated that this dissolution is suppressed by the addition of phosphate ligand, which is largely bioavailable in soils, especially in agricultural lands. This suppression was explained by the strong sorption of phosphate ligand to NP CeO2. The elimination of bioavailable Ce(III) release from NP CeO2 by phosphate ligand is likely one of the most important controls on toxicity effects and should be a large consideration in determining the fate and transport of NP CeO2 in the aquatic and terrestrial environment. It was also demonstrated that both Ce(III) and NP CeO2 have extremely strong affinity for sorption to soil matter, which could serve as another controlling pathway. Experiments indicated that factors such as reductive transformation of NP CeO2 in soils and exchangeable Ce(III) impurity in the NPs could contribute to controls on toxicity as well. In conclusion, the studies presented in this thesis indicate that the toxicity effects of the studied Ce species to soil denitrifiers are strongly affected by physical and chemical characteristics such as speciation, pH, and bioavailable ligands. As the global market for nanomaterials rapidly expands, so does the need of the scientific community for an understanding of how these influences in environmental fate and reactivity may be key in assessing toxicological risks associated with environmental exposures to NP CeO2 as well as other engineered metal oxide nanoparticles. (Abstract shortened by UMI.)

  16. EPR and optical studies of erbium-doped beta-PbF2 single-crystals and nanocrystals in transparent glass-ceramics.

    PubMed

    Dantelle, Géraldine; Mortier, Michel; Vivien, Daniel

    2007-11-01

    beta-PbF(2) single-crystals and nanocrystals in transparent glass-ceramics doped with ErF(3) have been synthesized and studied with two complementary techniques: electron paramagnetic resonance (EPR) and optical spectroscopy (absorption, selective excitation, fluorescence). A comparative study shows that, in both single-crystals and glass-ceramics, Er(3+) ions occupy the same types of sites, leading to similar optical properties. An EPR investigation demonstrates that, in these materials, part of the Er(3+) ions occupy cubic symmetry sites. For these ions, we determine the crystal field splitting of the ground state (4)I(15/2) and the symmetry of its sublevels. We also provide evidence for the presence of another type of Er(3+) ions, not detectable by EPR but evidenced by optical spectroscopy. We clearly show that this Er(3+), which gives rise to up-conversion luminescence, corresponds to clusters associating Er(3+) and F(-) ions. In the single-crystals, the proportion of these two types of erbium ions is estimated. It strongly depends on the doping rate of the beta-PbF(2) crystals.

  17. Effect of cobalt doping on structural, optical and redox properties cerium oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Ansari, Anees A.; Labis, J.; Alam, M.; Ramay, Shahid M.; Ahmad, N.; Mahmood, Asif

    2016-03-01

    Cobalt-doped ceria nanoparticles were synthesized using the polyol method under co-precipitation hydrolysis. The structural, morphological, optical and redox properties were observed to investigate the influence of different concentration of cobalt ion doping on the prepared CeO2 nanomaterials in terms of X-ray diffraction, field-emission transmission electron microscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, UV/vis absorption spectroscopy and temperature program reduction techniques. The optical band gap energy was calculated from the optical absorption spectra for doped ceria nanoparticles, which have been found to be 2.68, 2.77, and 2.82 eV for the 2, 4, and 7 mol% Co ion-doped CeO2 nanoparticles, respectively. As observed, the band gap energies increases as the doping Co ion concentrations increased, which could be due to significant increased oxygen vacancies with Co doping. The synergistic interaction between Co and CeO2 was the main factor responsible for high catalytic activity of cobalt-doped CeO2 model catalysts.

  18. Piezoelectric and dielectric properties of Sn-doped (Na0.5K0.5)NbO3 ceramics processed under low oxygen partial pressure atmosphere

    NASA Astrophysics Data System (ADS)

    Kobayashi, Keisuke; Doshida, Yutaka; Mizuno, Youichi; Randall, Clive A.

    2014-01-01

    Sn-doped (Na0.5K0.5)NbO3 (Sn-NKN) ceramics fired under various oxygen partial pressure (pO2) conditions have been investigated and discussed in terms of bulk piezoelectric and dielectric properties. X-ray diffraction measurements and Rayleigh analysis indicate that the substitution site of the Sn cations depend on the pO2 atmosphere in the firing process. For pO2 higher than 1.0 × 10-10 atm, Sn cations mainly substitute as Sn4+ at the B-site of perovskite NKN, whereas Sn2+ A-site substitution is favored under a low-pO2 atmosphere. Low-pO2 fired Sn-NKN ceramics exhibit higher relative permittivity, Curie temperature, and piezoelectric coefficient (d33). Sn2+ at A-site acts as a donor and reduces the p-type carrier concentrations that result from an electronic compensation of metal vacancies created through the high volatility of Na and K suboxides. The higher piezoelectricity and resistivity in low-pO2 fired Sn-NKN ceramics make this material suitable for base-metal cofired devices such as Ni-inner-electrode multilayer capacitors and actuators.

  19. Microstructure, optical, and scintillation characteristics of Pr{sup 3+} doped Lu{sub 3}Al{sub 5}O{sub 12} optical ceramics

    SciTech Connect

    Shi Yun; Feng Xiqi; Shen Yiqiang; Pan Yubai; Liu Qian; Nikl, Martin; Mares, Jiri A.; Beitlerova, A.; Kucerkova, R.

    2011-01-01

    0.5, 1.0, and 5.0 at. %Pr{sup 3+} doped Lu{sub 3}Al{sub 5}O{sub 12} (Pr:LuAG) optical ceramics are fabricated and compared with Bi{sub 4}Ge{sub 3}O{sub 12} (BGO) and Pr:LuAG single crystals as for their optical, luminescence and scintillation properties. Radio-luminescence intensity of the fast UV emission based on 5d{sub 1}{yields}4f Pr{sup 3+} transition reaches up to 20 times of that of BGO single crystal reference scintillator. Photoelectron yield of the best performing 0.5 at. % Pr:LuAG ceramic sample is about 1002 phels/MeV, about 30% lower than that of BGO reference sample and about 65% lower than that of Pr:LuAG single crystal. The trapping phenomena at grain boundaries and/or structural defects are proposed as the main cause of degradation of the scintillation response of the Pr:LuAG optical ceramics.

  20. Survey and research on up-conversion emission character and energy transition of Yb3+/Er3+/Tm3+ co-doped phosphate glass and glass ceramic

    NASA Astrophysics Data System (ADS)

    Yu, Yin; Song, Feng; Ming, Chengguo; Liu, Jiadong; Li, Wei; Liu, Yanling; Zhao, Hongyan

    2012-11-01

    By conventional high-temperature melting method, Yb3+/Er3+/Tm3+ co-doped phosphate glass was synthesized. After annealing the precursor glass, the phosphate glass ceramic (GC) was obtained. By measuring the X-ray diffraction (XRD) spectrum, it is proved that the LiYbP4O12 and Li6P6O18 nano-crystals have existed in the phosphate GC. The up-conversion (UC) emission intensity of the GC is obvious stronger compared to that of the glass. The reason is that the shorter distance between rare earth ions in the glass ceramic increases the energy transitions from the sensitized ions (Yb3+) to the luminous ions (Er3+ and Tm3+). By studying the dependence of UC emissions on the pump power, the 523 and 546 nm green emissions of Er3+ ions in the glass are two-photon processes. But in the glass ceramic, they are two/three-photon processes. The phenomenon implies that a three-photon process has participated in the population of the two green emissions. Using Dexter theory, we discuss the energy transitions of Er3+ and Tm3+. The results indicate the energy transition of Tm3+ to Er3+ is very strong in the GC, which changes the population mechanism of UC emissions of Er3+.

  1. The Effect of CeO2 Antireflection Layer on the Optical Properties of Thermochromic VO2 Film for Smart Window System

    NASA Astrophysics Data System (ADS)

    Koo, Hyun; Shin, Dongmin; Bae, Sung-Hwan; Ko, Kyeong-Eun; Chang, Se-Hong; Park, Chan

    2013-11-01

    CeO2-VO2 bilayer structure was fabricated to investigate the effect of depositing CeO2 film on the optical properties of VO2 film for smart window application. CeO2 was employed as an antireflection (AR) layer material of VO2 film because of its advantages which include high transparency in the visible-near infrared range and high refractive index. All the films were deposited on soda-lime glass substrate by pulsed laser deposition method. Optical calculations were carried out using transfer-matrix method for the purpose of designing CeO2-VO2 bilayer structure with enhanced integrated luminous transmittance (T lum) and switching efficiency (ΔT sol). The optical constants of VO2 and CeO2 films needed for the optical calculation were measured by spectroscopic ellipsometer. The curve of T lum the shape of which depends on the thickness of CeO2 layer, was calculated in each VO2 sample, which showed two maxima. The samples were divided into two groups; one for the highest enhancement of T lum and the other for balanced enhancement between T lum and ΔT sol. The sample with the structure of ~60 nm CeO2 AR layer on 39-nm thick VO2 film showed large increase of T lum (~27%) with ΔT sol of ~5%, which is the largest increase in T lum reported so far. Two samples in the other group showed the balanced enhancement in T lum (~57, ~50%) and ΔT sol (~9, ~10.5%). The effect of CeO2 AR layer on the optical properties of VO2 film was confirmed with the optical calculation and the experimental results. CeO2-VO2 bilayer structure showed notable improvement of optical properties compared to the single VO2 film, indicating that CeO2 layer can be effectively used as the antireflection layer while working as a protective layer that can prevent the oxidation of VO2 layer as well.

  2. Rose Bengal sensitized bilayered photoanode of nano-crystalline TiO2-CeO2 for dye-sensitized solar cell application

    NASA Astrophysics Data System (ADS)

    Sayyed, Suhail A. A. R.; Beedri, Niyamat I.; Kadam, Vishal S.; Pathan, Habib M.

    2016-08-01

    The present work deals with the study of TiO2-CeO2 bilayered photoanode with low-cost Rose Bengal (RB) dye as sensitizer for dye-sensitized solar cell application. The recombination reactions are reduced in bilayered TiO2-CeO2 photoanode as compared to the single-layered CeO2 photoanode. Once the electrons get transferred from lowest unoccupied molecular orbital level of RB dye to the conduction band (CB) of TiO2, then the possibilities of recombination of electrons with oxidized dye molecules or oxidized redox couple are reduced. This is because the CB position of CeO2 is higher than that of TiO2, which blocks the path of electrons. The electrochemical impedance spectroscopy (EIS) analysis shows negative shift in frequency for bilayered TiO2-CeO2 photoanode as compared to CeO2 photoanode. Hence, in bilayered photoanode lifetime of electrons is more than in single-layered photoanode, confirming reduction in recombination reactions. The X-ray diffraction patterns confirm both anatase TiO2 and CeO2 with crystalline size using Scherrer formula as 24 and 10 nm, respectively. The scanning electron microscopy images of photoanode show the porous structure useful for dye adsorption. The presence of Ti and Ce is confirmed by electron diffraction studies. The band gap values for TiO2 and CeO2 were calculated as 3.20 and 3.11 eV, respectively, using diffused reflectance spectroscopy. The bilayered TiO2-CeO2 photoanode showed open-circuit voltage ( V OC) ~500 mV and short-circuit photocurrent density ( J SC) ~0.29 mA/cm2 with fill factor (FF) ~62.17 %. There is increase in V OC and J SC values by 66.67 and 38.10 %, respectively, compared to RB-sensitized CeO2 photoanode.

  3. Toxicity of CeO2 nanoparticles at different trophic levels--effects on diatoms, chironomids and amphibians.

    PubMed

    Bour, Agathe; Mouchet, Florence; Verneuil, Laurent; Evariste, Lauris; Silvestre, Jérôme; Pinelli, Eric; Gauthier, Laury

    2015-02-01

    The aim of the present work is to provide wider information on the toxicity of cerium dioxide nanoparticles (CeO2 NPs) in aquatic environments, by studying the toxicity of two types of CeO2 NPs for four species (diatoms Nitzschia palea, the sediment-dwelling invertebrate Chironomus riparius, and the amphibian larvae Xenopus laevis and Pleurodeles waltl.). The two types of CeO2 NPs have different intrinsic properties: some of them are small citrate-coated spheres (2-5 nm), and the others are larger uncoated plates (20-60 nm). Acute toxicity (mortality at 48 or 96 h, depending on the test-organism) was assessed for the four species, from 0.1 to 100 mg L(-1) of NPs. Sub-lethal effects were assessed on chironomids exposed between 0.01 and 1 mg L(-1) of NPs. Mortality, growth inhibition and genotoxic effects were evaluated on amphibian larvae from 0.1 to 10 mg L(-1). Results reveal that no acute toxicity occurs on any species after short exposures, even at the highest concentrations. Mortality (35%) is observed on Xenopus larvae after 12d of exposure at the highest concentration of one type of NPs. No significant effects were observed on chironomids during chronic exposure. Xenopus larvae growth was inhibited from 1 mg L(-1) of both NPs while growth inhibition is observed on Pleurodeles only at the highest concentration of one type of NPs. No genotoxicity was observed on Xenopus but Pleurodeles exhibited dose-dependent genotoxic effects when exposed to one type of NPs. Observed differences in toxicity are discussed focusing on the studied compartment, routes of exposure, species and NPs.

  4. CeO2-TiO2 sorbents for the removal of elemental mercury from syngas.

    PubMed

    Zhou, Jinsong; Hou, Wenhui; Qi, Pan; Gao, Xiang; Luo, Zhongyang; Cen, Kefa

    2013-09-01

    A series of CeO2-TiO2 (CeTi) sorbents with different CeO2/TiO2 mass ratios were prepared by an impregnation method and employed to remove elemental mercury (Hg(0)) in simulated syngas. The CeTi sorbents with a CeO2/TiO2 mass ratio of 0.2 exhibited superior Hg(0) removal efficiency from 80 to 150 °C, which could be ascribed to the greater amount of surface chemisorbed oxygen resulted from Ce(3+) on the sample surface. H2S was the most effective syngas component responsible for Hg(0) removal. The use of 400 ppm H2S resulted in 98% Hg(0) removal efficiency under the experimental conditions. H2 and CO had a negligible effect on the efficiency of Hg removal. In the presence of H2S, a prohibitive effect of HCl and NH3 on Hg(0) removal was observed because of the consumption of the surface oxygen. Water vapor also inhibited Hg(0) removal due to competitive adsorption with H2S. Hg(0) removal over CeTi sorbents was proposed to follow the Eley-Rideal mechanism, in which active surface sulfur reacts with gas-phase Hg(0). This large oxygen storage capacity of CeTi sorbents is quite favorable to H2S catalytic oxidation and Hg(0) emission control in an extremely reducing environment, such as when there is a deficiency of O2.

  5. Fabrication and dye removal performance of magnetic CuFe2O4@CeO2 nanofibers

    NASA Astrophysics Data System (ADS)

    Zou, Lianli; Wang, Qiuju; Shen, Xiangqian; Wang, Zhou; Jing, Maoxiang; Luo, Zhou

    2015-03-01

    Novel magnetic adsorbents with CeO2 nanoparticles (about 20 nm) coated on CuFe2O4 nanofibers were fabricated by combining electrospinning technique and chemical precipitation methods. The prepared CuFe2O4@CeO2 composite nanofibers show a diameter of 200 nm with a high specific surface area of 64.12 m2/g. These composite nanofibers exhibit a typical soft-magnetic materials behavior with a specific saturation magnetization (Ms) of 20.51 Am2/kg. The adsorption performances of these composite nanofibers were evaluated by column bed studies for methyl orange (MO) removal from aqueous solution. The effect of pH, flow rate and dye concentration on adsorption performances were investigated. The results show that the adsorption capacity decreases with increase of pH. The largest adsorption capacity of the column beds shows about 100 g/mL under the condition of C0 = 0.05 mg/mL, F = 2.0 mL/min and pH 4.0. The kinetic process is described by Thomas model. The rate constant decreases with the extension of reaction time and decreasing pH. The desorption behaviors are also studied in 0.5 M NaCl solution, ethyl alcohol and deionized water, respectively, which show that the adsorbed MO molecules can be easily desorbed from CuFe2O4@CeO2 composite nanofibers in NaCl solution. The adsorption mechanism of ionic interaction, formation of hydrogen bonds and pore diffusion is rationally proposed.

  6. Extracellular Polymeric Substances (EPS) of Freshwater Biofilms Stabilize and Modify CeO2 and Ag Nanoparticles

    PubMed Central

    Kroll, Alexandra; Behra, Renata; Kaegi, Ralf; Sigg, Laura

    2014-01-01

    Streams are potential receiving compartments for engineered nanoparticles (NP). In streams, NP may remain dispersed or settle to the benthic compartment. Both dispersed and settling NP can accumulate in benthic biofilms called periphyton that are essential to stream ecosystems. Periphytic organisms excrete extracellular polymeric substances (EPS) that interact with any material reaching the biofilms. To understand the interaction of NP with periphyton it is therefore crucial to study the interaction of NP with EPS. We investigated the influence of EPS on the physicochemical properties of selected NP (CeO2, Ag) under controlled conditions at pH 6, 7.6, 8.6 and light or dark exposure. We extracted EPS from five different periphyton communities, characterized the extracts, and exposed CeO2 and carbonate-stabilized Ag NP (0.5 and 5 mg/L, both 25 nm primary particle size) and AgNO3 to EPS (10 mg/L) over two weeks. We measured NP size distribution, shape, primary particle size, surface plasmon resonance, and dissolution. All EPS extracts were composed of biopolymers, building blocks of humic substances, low molecular weight (Mr) acids, and small amphiphilic or neutral compounds in varying concentrations. CeO2 NP were stabilized by EPS independent of pH and light/dark while dissolution increased over time in the dark at pH 6. EPS induced a size increase in Ag NP in the light with decreasing pH and the formation of metallic Ag NP from AgNO3 at the same conditions via EPS-enhanced photoreduction. NP transformation and formation were slower in the extract with the lowest biopolymer and low Mr acid concentrations. Periphytic EPS in combination with naturally varying pH and light/dark conditions influence the properties of the Ag and CeO2 NP tested and thus the exposure conditions within biofilms. Our results indicate that periphytic organisms may be exposed to a constantly changing mixture of engineered and naturally formed Ag NP and Ag+. PMID:25333364

  7. Orange Peel Oxidative Gasification on Ni Catalysts Promoted with CaO, CeO2 or K2O.

    PubMed

    Vargas, G; Zapata, B; Valenzuela, M A; Alfaro, S

    2015-09-01

    Orange peel can be considered as an attractive raw material to be gasified for hydrogen or syngas production. In this work, the catalytic evaluation of several silica-supported nickel catalysts in the oxidative degradation of waste orange peel is reported. It was found that the catalytic gasification with the K2O-Ni/silica catalyst produces more hydrogen than the non-catalytic route at 600 degrees C. Surprisingly, a significant amount of ethene was obtained with the CeO2-Ni/silica catalyst, which was explained in terms of an oxidative dehydrogenation reaction of ethane formed during biomass or tar decomposition. PMID:26716225

  8. Citric acid modifies surface properties of commercial CeO2 nanoparticles reducing their toxicity and cerium uptake in radish (Raphanus sativus) seedlings.

    PubMed

    Trujillo-Reyes, J; Vilchis-Nestor, A R; Majumdar, S; Peralta-Videa, J R; Gardea-Torresdey, J L

    2013-12-15

    Little is known about the mobility, reactivity, and toxicity to plants of coated engineered nanoparticles (ENPs). Surface modification may change the interaction of ENPs with living organisms. This report describes surface changes in commercial CeO2 NPs coated with citric acid (CA) at molar ratios of 1:2, 1:3, 1:7, and 1:10 CeO2:CA, and their effects on radish (Raphanus sativus) seed germination, cerium and nutrients uptake. All CeO2 NPs and their absorption by radish plants were characterized by TEM, DLS, and ICP-OES. Radish seeds were germinated in pristine and CA coated CeO2 NPs suspensions at 50mg/L, 100mg/L, and 200mg/L. Deionized water and CA at 100mg/L were used as controls. Results showed ζ potential values of 21.6 mV and -56 mV for the pristine and CA coated CeO2 NPs, respectively. TEM images showed denser layers surrounding the CeO2 NPs at higher CA concentrations, as well as better distribution and smaller particle sizes. None of the treatments affected seed germination. However, at 200mg/L the CA coated NPs at 1:7 ratio produced significantly (p ≤ 0.05) more root biomass, increased water content and reduced by 94% the Ce uptake, compared to bare NPs. This suggests that CA coating decrease CeO2 NPs toxicity to plants. PMID:24231324

  9. Reel-to-reel continuous simultaneous double-sided deposition of highly textured CeO2 templates for YBa2Cu3O7-δ coated conductors

    NASA Astrophysics Data System (ADS)

    Xiong, J.; Tao, B. W.; Qin, W. F.; Tang, J. L.; Han, X.; Li, Y. R.

    2008-02-01

    A reel-to-reel system which allows simultaneous two-sided deposition of epitaxial CeO2 buffer layers on long length biaxially textured Ni-5 at.%W tape with direct current (dc) reactive magnetron sputtering is described. Deposition is accomplished through two opposite symmetrical sputtering guns with a radiation heater. Meter-long double-sided epitaxial CeO2 buffer layers have been produced for the first time on textured metal substrates in a run using a reel-to-reel process with a speed of about 1.2 m h-1. The CeO2 films were characterized by means of x-ray diffraction (XRD) and atomic force microscopy (AFM). The samples exhibited good epitaxial growth with the c-axis perpendicular to the substrate surface for both sides. Full width at half maximum (FWHM) values of the out-of-plane and in-plane orientation for both sides were 3.2° and 3.1°, 5.3° and 5.1°, respectively. AFM observations revealed a smooth, dense and crack-free surface morphology. In addition, x-ray scans have been performed as a function of length to determine the crystallographic consistency of the epitaxial CeO2 over the length. Subsequently anyttria-stabilized zirconia (YSZ) barrier and CeO2 cap layers were deposited to complete the CeO2/YSZ/CeO2 structure via the same process. Epitaxial YBa2Cu3O7-δ (YBCO) films grown by dc sputtering on the short prototype CeO2/YSZ/CeO2/NiW conductors yielded self-field critical current densities (Jc) as high as 1.3 MA cm-2 at 77 K. An Ic value of 113 A cm-1 was obtained for double-sided YBCO coated conductors.

  10. MnO(x) Nanoparticle-Dispersed CeO2 Nanocubes: A Remarkable Heteronanostructured System with Unusual Structural Characteristics and Superior Catalytic Performance.

    PubMed

    Putla, Sudarsanam; Amin, Mohamad Hassan; Reddy, Benjaram M; Nafady, Ayman; Al Farhan, Khalid A; Bhargava, Suresh K

    2015-08-01

    Understanding the interface-induced effects of heteronanostructured catalysts remains a significant challenge due to their structural complexity, but it is crucial for developing novel applied catalytic materials. This work reports a systematic characterization and catalytic evaluation of MnOx nanoparticle-dispersed CeO2 nanocubes for two important industrial applications, namely, diesel soot oxidation and continuous-flow benzylamine oxidation. The X-ray diffraction and Raman studies reveal an unusual lattice expansion in CeO2 after the addition of MnOx. This interesting observation is due to conversion of smaller sized Ce(4+) (0.097 nm) to larger sized Ce(3+) (0.114 nm) in cerium oxide led by the strong interaction between MnOx and CeO2 at their interface. Another striking observation noticed from transmission electron microscopy, high angle annular dark-field scanning transmission electron microscopy, and electron energy loss spectroscopy studies is that the MnOx species are well-dispersed along the edges of the CeO2 nanocubes. This remarkable decoration leads to an enhanced reducible nature of the cerium oxide at the MnOx/CeO2 interface. It was found that MnOx/CeO2 heteronanostructures efficiently catalyze soot oxidation at lower temperatures (50% soot conversion, T50 ∼660 K) compared with that of bare CeO2 nanocubes (T50 ∼723 K). Importantly, the MnOx/CeO2 heteronanostructures exhibit a noticeable steady performance in the oxidation of benzylamine with a high selectivity of the dibenzylimine product (∼94-98%) compared with that of CeO2 nanocubes (∼69-91%). The existence of a strong synergistic effect at the interface sites between the CeO2 and MnOx components is a key factor for outstanding catalytic efficiency of the MnOx/CeO2 heteronanostructures.

  11. Aspect Ratio Plays a Role in the Hazard Potential of CeO2 Nanoparticles in Mouse Lung and Zebrafish Gastrointestinal Tract

    PubMed Central

    Lin, Sijie; Wang, Xiang; Ji, Zhaoxia; Chang, Chong Hyun; Dong, Yuan; Meng, Huan; Liao, Yu-Pei; Wang, Meiying; Song, Tze-Bin; Kohan, Sirus; Xia, Tian; Zink, Jeffrey I.; Lin, Shuo; Nel, André E.

    2014-01-01

    We have previously demonstrated that there is a relationship between the aspect ratio (AR) of CeO2 nanoparticles and in vitro hazard potential. CeO2 nanorods with AR ≥ 22 induced lysosomal damage and progressive effects on IL-1β production and cytotoxicity in the human myeloid cell line, THP-1. In order to determine whether this toxicological paradigm for long aspect ratio (LAR) CeO2 is also relevant in vivo, we performed comparative studies in the mouse lung and gastrointestinal tract (GIT) of zebrafish larvae. Although oropharyngeal aspiration could induce acute lung inflammation for CeO2 nanospheres and nanorods, only the nanorods with the highest AR (C5) induced significant IL-1β and TGF-β1 production in the bronchoalveolar lavage fluid (BALF) at 21 days but not inducing pulmonary fibrosis. However, after a longer duration (44 days) exposure to 4 mg/kg of the C5 nanorods, more collagen production was seen with CeO2 nanorods vs. nanospheres after correcting for Ce lung burden. Using an oral-exposure model in zebrafish larvae, we demonstrated that C5 nanorods also induced significant growth inhibition, a decrease in body weight, and delayed vertebral calcification. In contrast, CeO2 nanospheres and shorter nanorods had no effect. Histological and transmission electron microscopy (TEM) analyses showed that the key injury mechanism of C5 was in the epithelial lining of the GIT, which demonstrated blunted microvilli and compromised digestive function. All considered, these data demonstrate that, similar to cellular studies, LAR CeO2 nanorods exhibit more toxicity in the lung and GIT, which could be relevant to inhalation and environmental hazard potential. PMID:24720650

  12. Enhanced microwave dielectric properties of Ba0.4Sr0.6TiO3 ceramics doping by metal Fe powders

    NASA Astrophysics Data System (ADS)

    Zhang, Qiwei; Zhai, Jiwei; Ben, Qianqian; Yu, Xian; Yao, Xi

    2012-11-01

    Ba0.4Sr0.6TiO3 ceramics by adding mental Fe powders have been fabricated via the solid-state reaction method. The microstructures and optical properties of samples are systematically studied in order to establish the effects of Fe powder additives on microwave dielectric properties of Ba0.4Sr0.6TiO3 ceramics by x-ray diffraction, x-ray photoelectron spectroscopy, and optical reflective spectrum. The results show the coexistence of Fe2+ and Fe3+ in Ba0.4Sr0.6TiO3 ceramics, the decrease of O vacancy concentrations, and their incorporation into the B-site (Ti) of the Ba0.4Sr0.6TiO3 host lattice give rise to excellent microwave dielectric properties. All samples have a higher Q value above 290 while maintaining relatively high tunability above 16.6%. In particular, the sample with the composition of x = 0.035 mol has the dielectric constant of 889, Q × f value of 826 (at 1.370 GHz), and tunability of 24%, which are very promising for high power tunable devices. In comparison, Fe2O3 oxide doped Ba0.4Sr0.6TiO3 ceramics with the same molar ratios of Fe exhibit inferior microwave properties. It indicates that additives of the metal Fe powders can more effectively improve dielectric properties of BaxSr1-xTiO3 system than Fe2O3 oxide.

  13. Enhanced microwave dielectric properties of Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics doping by metal Fe powders

    SciTech Connect

    Zhang Qiwei; Zhai Jiwei; Yao Xi; Ben Qianqian; Yu Xian

    2012-11-15

    Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics by adding mental Fe powders have been fabricated via the solid-state reaction method. The microstructures and optical properties of samples are systematically studied in order to establish the effects of Fe powder additives on microwave dielectric properties of Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics by x-ray diffraction, x-ray photoelectron spectroscopy, and optical reflective spectrum. The results show the coexistence of Fe{sup 2+} and Fe{sup 3+} in Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics, the decrease of O vacancy concentrations, and their incorporation into the B-site (Ti) of the Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} host lattice give rise to excellent microwave dielectric properties. All samples have a higher Q value above 290 while maintaining relatively high tunability above 16.6%. In particular, the sample with the composition of x = 0.035 mol has the dielectric constant of 889, Q Multiplication-Sign f value of 826 (at 1.370 GHz), and tunability of 24%, which are very promising for high power tunable devices. In comparison, Fe{sub 2}O{sub 3} oxide doped Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} ceramics with the same molar ratios of Fe exhibit inferior microwave properties. It indicates that additives of the metal Fe powders can more effectively improve dielectric properties of Ba{sub x}Sr{sub 1-x}TiO{sub 3} system than Fe{sub 2}O{sub 3} oxide.

  14. Structural characterization of Nd-doped Hf-zirconolite Ca 1-xNd xHfTi 2-xAl xO 7 ceramics

    NASA Astrophysics Data System (ADS)

    Caurant, Daniel; Loiseau, Pascal; Bardez, Isabelle

    2010-12-01

    Because of its high incorporation capacity and of the high thermal neutron capture cross-section of hafnium, Hf-zirconolite (CaHfTi 2O 7) ceramic can be envisaged as a potential waste form for minor actinides (Np, Am, Cm) and plutonium immobilization. In this work, Nd-doped Hf-zirconolite Ca 1-xNd xHfTi 2-xAl xO 7 ( x = 0; 0.01 and 0.2) ceramics have been prepared by solid state reaction. Neodymium has been used as trivalent actinide surrogate. The ceramic samples structure has been studied by X-ray diffraction and refined by the Rietveld method. This revealed that Nd 3+ ions only enter the Ca site, whereas part of Hf 4+ ions substitute titanium into Ti(1) sites and Al 3+ ions mainly occupy the Ti(2) split sites and Ti(3) sites of the zirconolite structure. Using various spectroscopic techniques (electron spin resonance, optical absorption and fluorescence), the environment of Nd 3+ cations in Hf-zirconolite has been studied and compared with that of Nd 3+ cations in Zr-zirconolite (CaZrTi 2O 7). Different local environments of Nd 3+ cations have been detected in Hf-zirconolite that can be attributed to the existence of an important disorder around Nd in the Ca site probably due to the statistical occupancy of the next nearest cationic site of neodymium (a split Ti site) by Ti 4+, Al 3+ cations and vacancies. No significant differences were observed concerning Nd 3+ cations environment and distribution in Hf- and Zr-zirconolite ceramics.

  15. Investigation on up-conversion luminescence properties of novel transparent Ho3+-Tm3+-Yb3+ co-doped oxyfluoride glass ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-bo; Han, Wan-lei; Xu, Fang; Song, Ying-lin

    2011-06-01

    In the present letter, the transparent oxyfluoride glass ceramics containing Ho3+-Tm3+-Yb3+:NaYF4 were successfully prepared by melt-quenching at 1400°C and subsequent heating at 650-680°C for 1~2 hours . X-ray diffraction (XRD) with Cu Kα radiation (λ=0.154nm) investigation revealed that NaYF4 nano-crystals in the glass ceramics was fabricated. Their sizes were determined by Sherrer's equation. The emission spectra red green and blue up-conversion (UC) under 980nm laser diode (LD) pumping and absorption spectra were measured. Luminescence measurements confirmed the partition of RE ions in nano-crystals NaYF4. The blue red and green UC radiations correspond to the transitions 1G4-3H6, 1G4-3H4 of Tm3+, 5F4, 5S2-5I8, 5F5-5I8, of Ho3+ ions, respectively. This is similar to that in Tm3+-Yb3+ and/or Ho3+-Yb3+ co-doped glass ceramics. To obtain upconversion fluorescence mechanisms, upconversion fluorescence intensity versus LD pump power were analyzed in view of energy levels of rare earth. Up-conversion mechanisms were discussed and the ratio between red, green and blue UC emission bands was found to be varied as a function of temperature of heat treatment and pump power. This result could be mainly attributed to the cross-relaxation between Ho3+ ions. The excellent optical properties and its convenient, low-cost synthesis of the present glass ceramic imply that it is an excellent substitution material for the unobtainable bulk NaYF4 crystal and may have potentially applications in tunable visible laser or many other fields.

  16. Down-shifting in Ce3+-Tb3+ co-doped SiO2-LaF3 nano-glass-ceramics for photon conversion in solar cells

    NASA Astrophysics Data System (ADS)

    Velázquez, J. J.; Rodríguez, V. D.; Yanes, A. C.; del-Castillo, J.; Méndez-Ramos, J.

    2012-10-01

    95SiO2-5LaF3 sol-gel derived nano-glass-ceramics single doped with Ce3+ or Tb3+ and co-doped with Ce3+-Tb3+ were synthesized by thermal treatment of precursor glasses. Precipitation of LaF3 nanocrystals during ceramming process was confirmed by X-ray diffraction with mean size ranging from 12 to 15 nm. An exhaustive spectroscopic analysis has been carried out. As a result, it was found that the green emission of Tb3+ ions was greatly enhanced through down shifting process, due to efficient energy transfer from Ce3+ to Tb3+ ions in the glass-ceramics, which is favored by the reduction of the interionic distances when the dopant ions are partitioned into LaF3 nanocrystals. These results suggest the use of these materials to improve the efficiency of solar cells.

  17. REACTIVE FORCE FIELDS FOR Y-DOPED BaZrO3 ELECTROLYTE AND NI-ANODE. POTENTIAL CATHODE MATERIALS FOR APPLICATION IN PROTON CERAMIC FUEL CELLS

    SciTech Connect

    Boris Merinov; Adri van Duin; Sossina Haile; William A. Goddard III

    2004-10-30

    Based on quantum mechanical data obtained for the Y-doped BaZrO{sub 3} electrolyte and Ni-anode Reactive Force Field parameters have been developed for further molecular dynamics simulations of the proton diffusion and electrode/electrolyte interfaces. Electronic and atomic structures of different terminations of the (001) BaZrO{sub 3} surface have been studied using first-principles calculations. Several potential cathode materials for the Y-doped BaZrO{sub 3} system were synthesized via glycine nitrate combustion method. Of the five potential cathode materials examined BaZr{sub 0.40}Pr{sub 0.40}Gd{sub 0.20}O{sub 3} and BaZr{sub 0.60}Y{sub 0.20}Co{sub 0.20}O{sub 3} appear to be the most promising for further applications in proton ceramic fuel cells. Fuel cell test of a Y-doped BaZrO{sub 3} thin film using platinum ink for both electrodes have been performed. The obtained results shows that a robust method for fabricating crack-free thin membranes, as well as methods for sealing anode and cathode chambers, have successfully been developed.

  18. Electrical and dielectric properties of ZnO and CeO{sub 2} doped ZrTi{sub 2}O{sub 6} ceramic

    SciTech Connect

    George, Aneesh; Thomas, Jijimon K.; John, Annamma; Solomon, Sam

    2014-01-28

    Zirconium oxide (ZrO{sub 2}) and titanium dioxide (TiO{sub 2}) are the important catalyst supports, since it has acidic and basic properties. The intermediate phase zirconium titanate ZrTi{sub 2}O{sub 6}, which is a solid solution with Zr:Ti ratio 1:2 has outstanding dielectric properties. The effects of doping of ZnO and CeO{sub 2} on the dielectric and electrical properties of ZrTi{sub 2}O{sub 6} ceramic are investigated. On adding 0.5 wt% ZnO, the dielectric constant is increased but, on adding CeO{sub 2}, the dielectric constant is decreased. The bulk density of pure sample sintered at 1530 °C is 91% of theoretical density while that of the doped samples sintered at 1450 °C is more than 94% of theoretical density. Scanning electron micrographs reveal that the samples are well sintered with minimum porosity. The semicircle behavior in the Cole-Cole plots at room temperature reveals that the samples are good ionic conductor. The induced impedance is reduced for doped samples and this can be used as a material for electrolyte in Solid Oxide Fuel Cell.

  19. Effects of nanocrystalline CeO2 supports on the properties and performance of Ni–Rh bimetallic catalyst for oxidative steam reforming of ethanol

    SciTech Connect

    Kugai, Junichiro; Subramani, Velu; Song, Chunshan; Engelhard, Mark H.; Chin, Ya-Huei

    2006-03-10

    This study focuses on the effects of the CeO2 support properties on the catalyst properties and performance of bimetallic Ni?Rh/CeO2 catalysts containing 5 wt% Ni and 1 wt% Rh for the oxidative steam reforming (OSR) of ethanol for hydrogen production and fuel cell applications. Three CeO2 supports with different crystal sizes and surface areas were examined. The surface areas of these supports increases in the order of CeO2-I (74 m2/g) < CeO2-II (92 m2/g) < CeO2-III (154 m2/g), but their crystallite sizes were about 10.2, 29.3, and 6.5 nm, respectively. The properties of Ni?Rh/CeO2 catalysts were investigated by XRD, TPR, H2 chemisorption, and in situ XPS techniques. The Rh metal dispersion increased while the Ni metal dispersion decreased with decreasing crystallite sizes of CeO2. TPR studies revealed the existence of a Rh?CeO2 metal?support interaction as well as Ni?Rh interaction in the Ni?Rh bimetallic catalyst supported on CeO2-III with a crystallite size of about 6.5 nm. The in situ XPS studies corroborated the TPR results. The reduced Ni and Rh species were reversibly oxidized, suggesting the existence of Ni?Rh redox species rather than NiRh surface alloy in the present catalyst system. The Rh species became highly dispersed when the crystallite size of CeO2 support was smaller. Comparing the catalytic performance in the OSR of ethanol was compared with the properties of the catalysts demonstrated that both ethanol conversion and H2 selectivity increased and the selectivity for undesirable byproducts decreased with increasing Rh metal dispersion. Best catalytic performance for OSR was achieved by supporting Ni?Rh bimetallic catalysts on the nanocrystalline CeO2-III. The Ni?Rh/CeO2-III catalyst exhibited stable activity and selectivity during on-stream operations at 450 C and as well as at 600 C.

  20. Designing CuOx Nanoparticle-Decorated CeO2 Nanocubes for Catalytic Soot Oxidation: Role of the Nanointerface in the Catalytic Performance of Heterostructured Nanomaterials.

    PubMed

    Sudarsanam, Putla; Hillary, Brendan; Mallesham, Baithy; Rao, Bolla Govinda; Amin, Mohamad Hassan; Nafady, Ayman; Alsalme, Ali M; Reddy, B Mahipal; Bhargava, Suresh K

    2016-03-01

    This work investigates the structure-activity properties of CuOx-decorated CeO2 nanocubes with a meticulous scrutiny on the role of the CuOx/CeO2 nanointerface in the catalytic oxidation of diesel soot, a critical environmental problem all over the world. For this, a systematic characterization of the materials has been undertaken using transmission electron microscopy (TEM), transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS), high-angle annular dark-field-scanning transmission electron microscopy (HAADF-STEM), scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS), X-ray diffraction (XRD), Raman, N2 adsorption-desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The TEM images show the formation of nanosized CeO2 cubes (∼25 nm) and CuOx nanoparticles (∼8.5 nm). The TEM-EDS elemental mapping images reveal the uniform decoration of CuOx nanoparticles on CeO2 nanocubes. The XPS and Raman studies show that the decoration of CuOx on CeO2 nanocubes leads to improved structural defects, such as higher concentrations of Ce(3+) ions and abundant oxygen vacancies. It was found that CuOx-decorated CeO2 nanocubes efficiently catalyze soot oxidation at a much lower temperature (T50 = 646 K, temperature at which 50% soot conversion is achieved) compared to that of pristine CeO2 nanocubes (T50 = 725 K) under tight contact conditions. Similarly, a huge 91 K difference in the T50 values of CuOx/CeO2 (T50 = 744 K) and pristine CeO2 (T50 = 835 K) was found in the loose-contact soot oxidation studies. The superior catalytic performance of CuOx-decorated CeO2 nanocubes is mainly attributed to the improved redox efficiency of CeO2 at the nanointerface sites of CuOx-CeO2, as evidenced by Ce M5,4 EELS analysis, supported by XRD, Raman, and XPS studies, a clear proof for the role of nanointerfaces in the performance of heterostructured nanocatalysts. PMID:26886079

  1. Designing CuOx Nanoparticle-Decorated CeO2 Nanocubes for Catalytic Soot Oxidation: Role of the Nanointerface in the Catalytic Performance of Heterostructured Nanomaterials.

    PubMed

    Sudarsanam, Putla; Hillary, Brendan; Mallesham, Baithy; Rao, Bolla Govinda; Amin, Mohamad Hassan; Nafady, Ayman; Alsalme, Ali M; Reddy, B Mahipal; Bhargava, Suresh K

    2016-03-01

    This work investigates the structure-activity properties of CuOx-decorated CeO2 nanocubes with a meticulous scrutiny on the role of the CuOx/CeO2 nanointerface in the catalytic oxidation of diesel soot, a critical environmental problem all over the world. For this, a systematic characterization of the materials has been undertaken using transmission electron microscopy (TEM), transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS), high-angle annular dark-field-scanning transmission electron microscopy (HAADF-STEM), scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS), X-ray diffraction (XRD), Raman, N2 adsorption-desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The TEM images show the formation of nanosized CeO2 cubes (∼25 nm) and CuOx nanoparticles (∼8.5 nm). The TEM-EDS elemental mapping images reveal the uniform decoration of CuOx nanoparticles on CeO2 nanocubes. The XPS and Raman studies show that the decoration of CuOx on CeO2 nanocubes leads to improved structural defects, such as higher concentrations of Ce(3+) ions and abundant oxygen vacancies. It was found that CuOx-decorated CeO2 nanocubes efficiently catalyze soot oxidation at a much lower temperature (T50 = 646 K, temperature at which 50% soot conversion is achieved) compared to that of pristine CeO2 nanocubes (T50 = 725 K) under tight contact conditions. Similarly, a huge 91 K difference in the T50 values of CuOx/CeO2 (T50 = 744 K) and pristine CeO2 (T50 = 835 K) was found in the loose-contact soot oxidation studies. The superior catalytic performance of CuOx-decorated CeO2 nanocubes is mainly attributed to the improved redox efficiency of CeO2 at the nanointerface sites of CuOx-CeO2, as evidenced by Ce M5,4 EELS analysis, supported by XRD, Raman, and XPS studies, a clear proof for the role of nanointerfaces in the performance of heterostructured nanocatalysts.

  2. Inclined Substrate Deposited CeO2 Films by Electron Beam Evaporation on Randomly Oriented Metallic Substrate

    NASA Astrophysics Data System (ADS)

    Mancini, A.; Celentano, G.; Fabbri, F.; Galluzzi, V.; Petrisor, T.; Rufoloni, A.; Varesi, E.; Vannozzi, A.; Rogai, R.; Boffa, V.; Gambardella, U.

    A study on CeO2 film growth on randomly oriented metallic substrate using lnclined Substrate Deposition (ISD) technique was performed in order to develop a biaxially aligned buffer layer for YBa2Cu3O7-δ (YBCO) coated conductors. The influence of deposition parameters, as the substrate inclination angle α with respect to the CeO2 vapor direction, deposition temperature and film thickness, on structural and morphological properties of the film was investigated. At substrate temperature between 200°C and 700°C a biaxial texture was observed for α ranging from 150° to 75°. The minimum value of the φ-scan full width at half maximum (FWHM) on (002) poles of about 13.5° was obtained for film 2 μm thick deposited at 200°C and α=55°. Morphological analyses on cross-sectioned samples revealed a columnar structure, typical for this deposition technique, with spaced grains and a tile like surface.

  3. Anchoring noble metal nanoparticles on CeO2 modified reduced graphene oxide nanosheets and their enhanced catalytic properties.

    PubMed

    Ji, Zhenyuan; Shen, Xiaoping; Xu, Yuling; Zhu, Guoxing; Chen, Kangmin

    2014-10-15

    The strategy of structurally integrating noble metal, metal oxide, and graphene is expected to offer prodigious opportunities toward emerging functions of graphene-based nanocomposites. In this study, we develop a facile two-step approach to disperse noble metal (Pt and Au) nanoparticles on the surface of CeO2 functionalized reduced graphene oxide (RGO) nanosheets. It is shown that Pt and Au with particle sizes of about 5 and 2nm are well dispersed on the surface of RGO/CeO2. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4 was used as a model reaction to quantitatively evaluate the catalytic properties of the as-synthesized RGO/Pt/CeO2 and RGO/Au/CeO2 ternary nanocomposites. In such triple-component catalysts, CeO2 nanocrystals provide unique and critical roles for optimizing the catalytic performance of noble metallic Pt and Au, allowing them to express enhanced catalytic activities in comparison with RGO/Pt and RGO/Au catalysts. In addition, a possible mechanism for the enhanced catalytic activities of the RGO/Pt/CeO2 and RGO/Au/CeO2 ternary catalysts in the reduction of 4-NP is proposed. It is expected that our prepared graphene-based triple-component composites, which inherit peculiar properties of graphene, metal oxide, and noble metal, are attractive candidates for catalysis and other applications.

  4. Hybrid nanocomposite from aniline and CeO2 nanoparticles: Surface protective performance on mild steel in acidic environment

    NASA Astrophysics Data System (ADS)

    Sasikumar, Y.; Kumar, A. Madhan; Gasem, Zuhair M.; Ebenso, Eno E.

    2015-03-01

    This present work contributes to the development of a new generation of active corrosion inhibitors composed of CeO2 nanoparticles covered with polyaniline that are able to release entrapped nanoparticles in acidic medium. Nanocomposites of aniline and CeO2 nanoparticles have been chemically synthesized by in-situ polymerization. The structural evolutions and morphological characteristics of PANI/CeO2 nanocomposite (PCN) have performed using various techniques such as XRD, IR, XPS, SEM and TEM analysis. It was illustrated from SEM and TEM observation that the PCN has globular particle with core-shell structure. The inhibition properties of synthesized PCN on mild steel (MS) corrosion in 0.5 M HCl were estimated using weight loss and electrochemical techniques. Potentiodynamic polarization results revealed PCN to be a mixed-type inhibitor, while impedance results indicate the adsorption of the PCN film on the MS surface. The inhibition efficiency of PCN was found to increase almost linearly with concentration. Moreover, an increase in the water contact-angle with PCN indicated its adsorption at the MS surface, and ATR-IR, SEM/EDAX and AFM visualization confirmed the formation of a protective film adsorbed on a MS surface. Finally, it was concluded that the PCN is a potential inhibitor for mild steel in HCl medium.

  5. Performance of the nano-structured Cu-Ni (alloy) -CeO2 anode for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Liu, Minquan; Wang, Shaolan; Chen, Ting; Yuan, Chun; Zhou, Yucun; Wang, Shaorong; Huang, Jun

    2015-01-01

    In this work, copper and nickel oxides (CuO-NiO) powders with various mole ratios were synthesized by the glycine nitrate process (GNP) and the Cu-Ni alloy was obtained by reducing the CuO-NiO powders at 600 °C for 0.75 h. Furthermore, Cu1-xNix (alloy) -CeO2 impregnated YSZ anodes were fabricated by the impregnation method and the optimized anode composition was evaluated. It was found that the optimized mole ratio of Cu:Ni was 5:5, while the weight ratio of Cu-Ni alloy to CeO2 was 3:1. Additionally, impregnated anode with 40 wt % loading of Cu0.5Ni0.5 (alloy)-CeO2 exhibited the best performance and the polarization resistance of such anode was only 0.097, 0.115, 0.145 and 0.212 Ω cm2 at 750, 700, 650 and 600 °C, respectively. Finally, the performance of the optimized anode in methane (CH4) was investigated and the carbon deposition is greatly suppressed compared to the Ni-based anode.

  6. Shape tailored green synthesis of CeO2:Ho3+ nanopowders, its structural, photoluminescence and gamma radiation sensing properties

    NASA Astrophysics Data System (ADS)

    Malleshappa, J.; Nagabhushana, H.; Kavyashree, D.; Prashantha, S. C.; Sharma, S. C.; Premkumar, H. B.; Shivakumara, C.

    2015-06-01

    CeO2:Ho3+ (1-9 mol%) nanopowders have been prepared by efficient and environmental friendly green combustion method using Aloe vera gel as fuel for the first time. The final products are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), fourier transform infrared (FTIR). Bell, urchin, core shell and flower like morphologies are observed with different concentrations of the A. vera gel. It is apparent that by adjusting the concentration of the gel, considerable changes in the formation of CeO2:Ho3+ nano structures can be achieved. Photoluminescence (PL) studies show green (543, 548 nm) and red (645, 732 nm) emissions upon excited at 400 nm wavelength. The emission peaks at ∼526, 548, 655 and 732 nm are associated with the transitions of 5F3 → 5I8, 5S2 → 5I8, 5F5 → 5I8 and 5S2 → 5I7, respectively. Three TL glow peaks are observed at 118, 267 and 204 °C for all the γ irradiated samples which specify the surface and deeper traps. Linear TL response in the range 0.1-2 kGy shows that phosphor is fairly useful as γ radiation dosimeter. Kinetic parameters associated with the glow peaks are estimated using Chen's half width method. The CIE coordinate values show that phosphor is quite useful for the possible applications in WLEDs as orange red phosphor.

  7. Adsorption and Reaction of Acetaldehyde on Shape-Controlled CeO2 Nanocrystals: Elucidation of Structure-function Relationships

    SciTech Connect

    Mann, Amanda K; Wu, Zili; Calaza, Florencia; Overbury, Steven {Steve} H

    2014-01-01

    CeO2 cubes with {100} facets, octahedra with {111} facets, and wires with highly defective structures were utilized to probe the structure-dependent reactivity of acetaldehyde. Using temperature-programmed desorption (TPD), temperature-programmed surface reactions (TPSR), and in situ infrared spectroscopy it was found that acetaldehyde desorbs unreacted or undergoes reduction, coupling, or C-C bond scission reactions depending on the surface structure of CeO2. Room temperature FTIR indicates that acetaldehyde binds primarily as 1-acetaldehyde on the octahedra, in a variety of conformations on the cubes, including coupling products and acetate and enolate species, and primarily as coupling products on the wires. The percent consumption of acetaldehyde follows the order of wires > cubes > octahedra. All the nanoshapes produce the coupling product crotonaldehyde; however, the selectivity to produce ethanol follows the order wires cubes >> octahedra. The selectivity and other differences can be attributed to the variation in the basicity of the surfaces, defects densities, coordination numbers of surface atoms, and the reducibility of the nanoshapes.

  8. Enhanced Gas Sensing Properties of SnO2 Hollow Spheres Decorated with CeO2 Nanoparticles Heterostructure Composite Materials.

    PubMed

    Liu, Jiangyang; Dai, Mingjun; Wang, Tianshuang; Sun, Peng; Liang, Xishuang; Lu, Geyu; Shimanoe, Kengo; Yamazoe, Noboru

    2016-03-01

    CeO2 decorated SnO2 hollow spheres were successfully synthesized via a two-step hydrothermal strategy. The morphology and structures of as-obtained CeO2/SnO2 composites were analyzed by various kinds of techniques. The SnO2 hollow spheres with uniform size around 300 nm were self-assembled with SnO2 nanoparticles and were hollow with a diameter of about 100 nm. The CeO2 nanoparticles on the surface of SnO2 hollow spheres could be clearly observed. X-ray photoelectron spectroscopy results confirmed the existence of Ce(3+) and the increased amount of both chemisorbed oxygen and oxygen vacancy after the CeO2 decorated. Compared with pure SnO2 hollow spheres, such composites revealed excellent enhanced sensing properties to ethanol. When the ethanol concentration was 100 ppm, the sensitivity of the CeO2/SnO2 composites was 37, which was 2.65-times higher than that of the primary SnO2 hollow spheres. The sensing mechanism of the enhanced gas sensing properties was also discussed.

  9. Synthesis of Dimethyl Carbonate from Ethylene Carbonate and Methanol Over Nano-Catalysts Supported on CeO2-MgO.

    PubMed

    Jun, Jin Oh; Lee, Joongwon; Kang, Ki Hyuk; Song, In Kyu

    2015-10-01

    A series of CeO2(X)-MgO(1-X) (X = 0, 0.25, 0.5, 0.75, and 1.0) nano-catalysts were prepared by a co-precipitation method for use in the synthesis of dimethyl carbonate from ethylene carbonate and methanol. Among the CeO2(X)-MgO(1-X) catalysts, CeO2(0.25)-MgO(0.75) nano-catalyst showed the best catalytic performance. Alkali and alkaline earth metal oxides (MO = Li2O, K2O, Cs2O, SrO, and BaO) were then supported on CeO2(0.25)-MgO(0.75) by an incipient wetness impregnation method with an aim of improving the catalytic performance of CeO2(0.25)-MgO(0.75). Basicity of the catalysts was determined by CO2-TPD experiments in order to elucidate the effect of basicity on the catalytic performance. The correlation between catalytic performance and basicity showed that basicity played an important role in the reaction. Yield for dimethyl carbonate increased with increasing basicity of the catalysts. Among the catalysts tested, Li2O/CeO2(0.25)-MgO(0.75) nano-catalyst with the largest basicity showed the best catalytic performance in the synthesis of dimethyl carbonate.

  10. CeO2 nanocubes-graphene oxide as durable and highly active catalyst support for proton exchange membrane fuel cell.

    PubMed

    Lei, M; Wang, Z B; Li, J S; Tang, H L; Liu, W J; Wang, Y G

    2014-01-01

    Rapid degradation of cell performance still remains a significant challenge for proton exchange membrane fuel cell (PEMFC). In this work, we develop novel CeO2 nanocubes-graphene oxide nanocomposites as durable and highly active catalyst support for proton exchange membrane fuel cell. We show that the use of CeO2 as the radical scavenger in the catalysts remarkably improves the durability of the catalyst. The catalytic activity retention of Pt-graphene oxide-8 wt.% CeO2 nanocomposites reaches as high as 69% after 5000 CV-cycles at a high voltage range of 0.8-1.23 V, in contrast to 19% for that of the Pt-graphene oxide composites. The excellent durability of the Pt-CeO2 nanocubes-graphene oxide catalyst is attributed to the free radical scavenging activity of CeO2, which significantly slows down the chemical degradation of Nafion binder in catalytic layers, and then alleviates the decay of Pt catalysts, resulting in the excellent cycle life of Pt-CeO2-graphene oxide nanocomposite catalysts. Additionally, the performance of single cell assembled with Nafion 211 membrane and Pt-CeO2-graphene oxide catalysts with different CeO2 contents in the cathode as well as the Pt-C catalysts in the anode are also recorded and discussed in this study.

  11. Effects of CeO2 nanoparticles on biological nitrogen removal in a sequencing batch biofilm reactor and mechanism of toxicity.

    PubMed

    Hou, Jun; You, Guoxiang; Xu, Yi; Wang, Chao; Wang, Peifang; Miao, Lingzhan; Ao, Yanhui; Li, Yi; Lv, Bowen

    2015-09-01

    The effects of CeO2 nanoparticles (CeO2 NPs) exposure on biological nitrogen removal in a sequencing batch biofilm reactor (SBBR) were investigated. At low concentration (1 mg/L), no significant effect was observed on total nitrogen (TN) removal. However, at high concentrations (10 and 50 mg/L), the TN removal efficiency reduced from 74.09% to 64.26% and 55.17%, respectively. Scanning electron microscope imaging showed large amounts of CeO2 NPs adsorbed on the biofilm, which increased the production of reactive oxygen species. The exposure at only 50 mg/L CeO2 NPs measurably affected the lactate dehydrogenase release. Confocal laser scanning microscopy showed that high concentrations of CeO2 NPs reduced bacterial viability. Moreover, after a short-term exposure, extracellular polymeric substances (EPS) were observed to increase, forming a compact matrix to protect the bacteria. The activities of nitrate reductase and ammonia monooxygenase were inhibited, but there was no significant impact on the activity of nitrite oxidoreductase.

  12. CeO2 nanocubes-graphene oxide as durable and highly active catalyst support for proton exchange membrane fuel cell

    PubMed Central

    Lei, M.; Wang, Z. B.; Li, J. S.; Tang, H. L.; Liu, W. J.; Wang, Y. G.

    2014-01-01

    Rapid degradation of cell performance still remains a significant challenge for proton exchange membrane fuel cell (PEMFC). In this work, we develop novel CeO2 nanocubes-graphene oxide nanocomposites as durable and highly active catalyst support for proton exchange membrane fuel cell. We show that the use of CeO2 as the radical scavenger in the catalysts remarkably improves the durability of the catalyst. The catalytic activity retention of Pt-graphene oxide-8 wt.% CeO2 nanocomposites reaches as high as 69% after 5000 CV-cycles at a high voltage range of 0.8–1.23 V, in contrast to 19% for that of the Pt-graphene oxide composites. The excellent durability of the Pt-CeO2 nanocubes-graphene oxide catalyst is attributed to the free radical scavenging activity of CeO2, which significantly slows down the chemical degradation of Nafion binder in catalytic layers, and then alleviates the decay of Pt catalysts, resulting in the excellent cycle life of Pt-CeO2-graphene oxide nanocomposite catalysts. Additionally, the performance of single cell assembled with Nafion 211 membrane and Pt-CeO2-graphene oxide catalysts with different CeO2 contents in the cathode as well as the Pt-C catalysts in the anode are also recorded and discussed in this study. PMID:25491655

  13. Optimized CeO2 content of the carbon nanofiber support of PtRu catalyst for direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Kunitomo, Hikari; Ishitobi, Hirokazu; Nakagawa, Nobuyoshi

    2015-11-01

    A series of CeO2 embedded carbon nanofibers, CECNFs, with different CeO2 contents was prepared by an electrospinning technique. About 15 wt% PtRu nanoparticles were deposited on the fibers, and the effect of the CeO2 content on the methanol oxidation activity of the catalyst, PtRu/CECNF, was investigated. Cyclic voltammetry (CV), chronoamperometry (CA) and CO stripping electrochemical measurements and physical characterization along with X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were carried out on the prepared catalysts. The mass activity of the PtRu was significantly increased by the CeO2 addition up to Ce/C = 0.4, and the maximized activity was 2 times higher than that without CeO2. The increased activity was attributed to the strong interaction between the metal and oxide in the embedded nanofiber structure. A DMFC with the PtRu/CECNF exhibited more than 2.5 times high power density with one half the PtRu loading compared to that of the commercial catalyst, PtRu/Ccom.

  14. Photoluminescence, photocatalytic and antibacterial activities of CeO2·CuO·ZnO nanocomposite fabricated by co-precipitation method.

    PubMed

    Subhan, Md Abdus; Uddin, Nizam; Sarker, Prosenjit; Azad, Abul Kalam; Begum, Kulsuma

    2015-10-01

    A novel tri-metallic oxide nanocomposite CeO2·CuO·ZnO has been synthesized by a simple co-precipitation method. The nanocomposite has been characterized by XRD, SEM, EDS, FTIR and PL spectra. The crystallite size of the CeO2·CuO·ZnO was calculated using XRD data. The crystallite size of the CeO2·CuO·ZnO mixed metal oxide annealed at 600 °C is found to be in range of 15.34-44.81 nm, with an average size of 29.51 nm. Excitation at different wavelengths showed PL in UV and visible regions. It has been found that PL behavior of CeO2·CuO·ZnO is excitation wavelength dependent. This flexible PL property is conflicting to well-known Kasha's rule of excitation wavelength dependence of emission spectrum. The catalyst shows better photo-catalytic dye degradation efficiency in slightly alkaline pH in presence of H2O2. Nanocomposite CeO2·CuO·ZnO was found to be effective against pathogenic bacteria. PMID:26002435

  15. Structure and photoluminescence studies of CeO2·CuAlO2 mixed metal oxide fabricated by co-precipitation method

    NASA Astrophysics Data System (ADS)

    Subhan, Md Abdus; Ahmed, Tanzir; Awal, M. R.; Kim, B. Moon

    2015-01-01

    A novel mixed metal oxide, CeO2·CuAlO2 was fabricated by co-precipitation method in aqueous medium. CeO2·CuAlO2 was characterized by XRD, SEM, EDS, TEM, FTIR and PL spectra. The optical properties of the nanoparticles were studied by photoluminescence (PL) spectra. PL spectra at different excitations were recorded. The composite showed emission in UV, visible and NIR region depending on the excitation wavelength. The special spectral feature observed for this composite is that it showed six emission bands at 364, 409, 434, 448, 465 and 481 nm when excited at 298 nm. The green and red emissions observed at 512 and 669 nm are originated from cubic CeO2 phase when excited at 450 nm. The PL spectra were found to be dependent on excitation wavelength violating Kasha's rule. The X-ray diffraction reveals a cubic CeO2 phase and hexagonal CuAlO2 phase. EDS spectra revealed the presence of cerium (Ce), copper (Cu), aluminum (Al) and oxygen (O) elements. The particle size of the CeO2·CuAlO2 mixed oxide was estimated using Scherrer's formula, which was found to be in the range of 17.2-34.2 nm. The TEM image showed particles are almost uniform size of approximately 15-50 nm with spherical morphology.

  16. Structure and photoluminescence studies of CeO2·CuAlO2 mixed metal oxide fabricated by co-precipitation method.

    PubMed

    Subhan, Md Abdus; Ahmed, Tanzir; Awal, M R; Kim, B Moon

    2015-01-25

    A novel mixed metal oxide, CeO2·CuAlO2 was fabricated by co-precipitation method in aqueous medium. CeO2·CuAlO2 was characterized by XRD, SEM, EDS, TEM, FTIR and PL spectra. The optical properties of the nanoparticles were studied by photoluminescence (PL) spectra. PL spectra at different excitations were recorded. The composite showed emission in UV, visible and NIR region depending on the excitation wavelength. The special spectral feature observed for this composite is that it showed six emission bands at 364, 409, 434, 448, 465 and 481 nm when excited at 298 nm. The green and red emissions observed at 512 and 669 nm are originated from cubic CeO2 phase when excited at 450 nm. The PL spectra were found to be dependent on excitation wavelength violating Kasha's rule. The X-ray diffraction reveals a cubic CeO2 phase and hexagonal CuAlO2 phase. EDS spectra revealed the presence of cerium (Ce), copper (Cu), aluminum (Al) and oxygen (O) elements. The particle size of the CeO2·CuAlO2 mixed oxide was estimated using Scherrer's formula, which was found to be in the range of 17.2-34.2 nm. The TEM image showed particles are almost uniform size of approximately 15-50 nm with spherical morphology. PMID:25113734

  17. Synthesis of Dimethyl Carbonate from Ethylene Carbonate and Methanol Over Nano-Catalysts Supported on CeO2-MgO.

    PubMed

    Jun, Jin Oh; Lee, Joongwon; Kang, Ki Hyuk; Song, In Kyu

    2015-10-01

    A series of CeO2(X)-MgO(1-X) (X = 0, 0.25, 0.5, 0.75, and 1.0) nano-catalysts were prepared by a co-precipitation method for use in the synthesis of dimethyl carbonate from ethylene carbonate and methanol. Among the CeO2(X)-MgO(1-X) catalysts, CeO2(0.25)-MgO(0.75) nano-catalyst showed the best catalytic performance. Alkali and alkaline earth metal oxides (MO = Li2O, K2O, Cs2O, SrO, and BaO) were then supported on CeO2(0.25)-MgO(0.75) by an incipient wetness impregnation method with an aim of improving the catalytic performance of CeO2(0.25)-MgO(0.75). Basicity of the catalysts was determined by CO2-TPD experiments in order to elucidate the effect of basicity on the catalytic performance. The correlation between catalytic performance and basicity showed that basicity played an important role in the reaction. Yield for dimethyl carbonate increased with increasing basicity of the catalysts. Among the catalysts tested, Li2O/CeO2(0.25)-MgO(0.75) nano-catalyst with the largest basicity showed the best catalytic performance in the synthesis of dimethyl carbonate. PMID:26726512

  18. Preparation of bi-axially aligned YBa 2Cu 3O 7- δ film on CeO 2-buffered MgO by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Yamagiwa, K.; Hiei, H.; Takahashi, Y.; Kim, S. B.; Matsumoto, K.; Ikuta, H.; Mizutani, U.; Hirabayashi, I.

    2000-06-01

    We have succeeded in preparing in-plane aligned YBa 2Cu 3O 7- δ (Y123) film by chemical solution deposition (CSD) processing on CeO 2 (100)-buffered MgO (100) substrates. The CeO 2 buffer film was deposited on MgO (100) single crystalline substrate by pulsed laser deposition (PLD). For CSD coating, a homogeneous coating solution having a molar ratio of Y:Ba:Cu=1:2:3, was prepared by dissolving metal naphthenates in toluene. This solution was spin-coated both on the YSZ (100) and on the CeO 2-buffered MgO (100) single crystalline substrates. The precursor films were calcined at 425°C and fired at various temperatures under low oxygen partial pressure ( pO 2). All Y123 films showed strong (00 n) peaks, which correspond to c-axis orientation perpendicular to the substrates and their a/ b-axes were in-plane aligned. We confirmed that CeO 2 buffer is usable for CSD processing. While the Y123 films on the YSZ reacted with the substrate forming BaZrO 3 phase and did not show sufficient superconducting properties. The Tc,zero value of the Y123 film prepared on CeO 2-buffered MgO substrate was 91.5 K and Jc was 1.2×10 5 A/cm 2 at 77 K, 0 T.

  19. Crystal field disorder effects in the optical spectra of Nd{sup 3+} and Yb{sup 3+}-doped calcium lithium niobium gallium garnets laser crystals and ceramics

    SciTech Connect

    Lupei, V.; Lupei, A.; Gheorghe, C.; Gheorghe, L.; Achim, A.; Ikesue, A.

    2012-09-15

    The optical spectroscopic properties of RE{sup 3+} (Nd, 1 at. % or Yb, 1 to 10 at. %)-doped calcium-lithium-niobium-gallium garnet (CLNGG) single crystals and ceramics in the 10 K-300 K range are analyzed. In these compositionally disordered materials, RE{sup 3+} substitute Ca{sup 2+} in dodecahedral sites and the charge compensation is accomplished by adjusting the proportion of Li{sup +}, Nb{sup 5+}, and Ga{sup 3+} to the doping concentration. The crystals and ceramics show similar optical spectra, with broad and structured (especially at low temperatures) bands whose shape depends on temperature and doping concentration. At 10 K, the Nd{sup 3+4}I{sub 9/2}{yields}{sup 4}F{sub 3/2,5/2} and Yb{sup 3+2}F{sub 7/2}{yields}{sup 2}F{sub 5/2} absorption bands, which show prospect for diode laser pumping, can be decomposed in several lines that can be attributed to centers with large differences in the crystal field. The positions of these components are the same, but the relative intensity depends on the doping concentration and two main centers dominate the spectra. Non-selective excitation evidences broad emission bands, of prospect for short-pulse laser emission, whereas the selective excitation reveals the particular emission spectra of the various centers. The modeling reveals that the nonequivalent centers correspond to RE{sup 3+} ions with different cationic combinations in the nearest octahedral and tetrahedral coordination spheres, and the most abundant two centers have 4Nb and, respectively, 3Nb1Li in the nearest octahedral sphere. At 300 K, the spectral resolution is lost. It is then inferred that the observed optical bands are envelopes of the spectra of various structural centers, whose resolution is determined by the relative contribution of the temperature-dependent homogeneous broadening and the effects of crystal field disordering (multicenter structure, inhomogeneous broadening). The relevance of spectroscopic properties for selection of pumping

  20. Effects of doping, cation stoichiometry, and the processing conditions on the dielectric properties of high-K calcium copper titanate ceramics

    NASA Astrophysics Data System (ADS)

    Kwon, Seunghwa

    Since its discovery, the anomalous dielectric behavior of CaCu3 Ti4O12 (CCTO) has drawn a great deal of attention for many possible applications in electronic devices. The origin of the giant dielectric constant in CCTO was explained via an internal barrier layer capacitor model, and it has been reported that the dielectric properties of CCTO are sensitive to its microstructure which depends upon the processing conditions. To further explore its unusual dielectric phenomena, the current study focuses on the process-property-structure relationship of the high-K CCTO via doping, cation non-stoichiometry, and sintering conditions. A variety of CCTO pellets were obtained by utilizing the different processing parameters via conventional solid-state synthesis methods. For the doping study, three types of dopants were selected with the variation of doping concentration. The study of undoped CCTO ceramics was carried out by the modification of the CuO and TiO2 content in CCTO to create the stoichiometric formula CaCu3+xTi4+yO12 (x = -0.06, 0, -0.06; y = 0.08, 0, -0.08). Different processing factors including heating and cooling rates, sintering temperature, and sintering time were applied for the study of stoichiometric CCTO. X-ray diffraction, dielectric measurements, impedance spectroscopy, thermal analysis, and electron microprobe analysis were used to determine the existence of CuO and Cu2O secondary phases, dielectric constant and loss tangent, electrical resistivity of grains and boundaries, decomposition reactions, and the microstructural changes of CCTO ceramics. It was revealed that the doping method improved the dielectric constant and loss tangent. The similar improvement in dielectric properties was also found in the Cu-deficient and Ti-deficient CCTO. The measurement and characterization results of stoichiometric CCTO clearly indicated that the dielectric properties, evolution of secondary phases, and microstructures were strongly dependent upon the processing

  1. Enhanced thermoelectric properties of the hole-doped Bi2-xKxSr2Co2Oy ceramics

    NASA Astrophysics Data System (ADS)

    Gao, Feng; He, Qinglin; Cao, Ruijuan; Wu, Fang; Hu, Xing; Song, Hongzhang

    2015-09-01

    In this paper, the influence of K element doping on the thermoelectric properties of the Bi2-xKxSr2Co2Oy (x = 0.00, 0.05, 0.10, 0.15, and 0.20) samples prepared by the solid-state reaction method were investigated from 333 K to 973 K. It was shown that due to the p-type K doping the electrical resistivity of the doped sample can be reduced remarkably as compared with the undoped sample, especially for the optimum doped sample Bi1.9K0.1Sr2Co2Oy. The Seebeck coefficients of the K doped samples have only a slight decrease as compared with the undoped sample. As a result of the remarkable reduction of the electrical resistivity the power factor of the doped sample have a significant improvement. The thermal conductivity of the samples is depressed due to the defects caused by K doping. As an overall result, the dimensionless figure of merit (ZT) of the Bi1.9K0.1Sr2Co2Oy sample reaches a maximum value of 0.3 at 973 K, being 93% higher than that of the undoped sample.

  2. Energy storage property in lead free gd doped Na1/2Bi1/2TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Zannen, Moneim; Lahmar, Abdelilah; Khemakhem, Hamadi; El Marssi, Mimoun

    2016-11-01

    The Effect of Gadolinium ion incorporation on structure, dielectric and ferroelectric properties of lead-free Na1/2Bi1/2TiO3 (NBT) ceramic was investigated. X-ray diffraction allowed the identification of a pure phase isostructural to NBT. Dielectric measurements showed more pronounced anomalies in the range of depolarization temperature when Gd was added. Antiferroelectric-like behavior with a double pinched hysteresis loop was observed versus temperature in the doped phase. The energy-storage density (W) was calculated using the P-E loops data and was found to vary from 0.45 J cm-3 at room temperature to 0.85 J cm-3 at 413 K, which is promising for energy storage application.

  3. Dielectric behavior of samarium-doped BaZr{sub 0.2}Ti{sub 0.8}O{sub 3} ceramics

    SciTech Connect

    Li, Yuanliang; Wang, Ranran; Ma, Xuegang; Li, Zhongqiu; Sang, Rongli; Qu, Yuanfang

    2014-01-01

    Graphical abstract: - Highlights: • We investigate dielectric properties and phase transition of Sm{sup 3+}-doped BaZr{sub 0.2}Ti{sub 0.8}O{sub 3} ceramics. • The additive amount of Sm{sub 2}O{sub 3} can greatly affect the dielectric properties. • The materials undergo a diffuse type ferroelectric phase transition. • There is an alternation of substitution preference of Sm{sup 3+} ion for the host cations in perovskite lattice. - Abstract: The dielectric properties and phase transition of Sm{sup 3+}-doped BaZr{sub 0.2}Ti{sub 0.8}O{sub 3} (BZT20) ceramics were investigated. Room temperature X-ray diffraction study suggested that the compositions had single-phase cubic symmetry. Microstructure studies showed that the grain size decreased and that the Sm{sub 2}O{sub 3} amount markedly affected the dielectric properties of BZT20. A dielectric constant of 5700 at 0.2 mol% Sm{sub 2}O{sub 3} and a dissipation factor of only 0.0011 at 2 mol% Sm{sub 2}O{sub 3} were observed, indicating that BZT20 had significant potential applications. Moreover, the dielectric constant, dissipation factor, phase-transition temperature, and maximum dielectric constant increased with increased Sm{sub 2}O{sub 3} amount at ≤0.2 mol% Sm{sub 2}O{sub 3} but decreased with increased Sm{sub 2}O{sub 3} amount at >0.2 mol% Sm{sub 2}O{sub 3}.

  4. The effect of CuO and NiO doping on dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Kakroo, Sunanda; Kumar, Arvind; Mishra, S. K.; Singh, Vijay; Singh, Pramod K.

    2016-03-01

    In the present work, lead-free piezoelectric ceramics (Na0.5Bi0.5)TiO3 -xCuO-yNiO (for x = 0.0, 0.02, 0.04 and 0.06) have been prepared by a conventional solid-state reaction method. An investigation of CuO and NiO doping in bismuth sodium titanate (BNT) and a study of the structure, morphology, and dielectric and ferroelectric properties of the NBT-CuNi system have been conducted. Phase and microstructural analysis of the (Na0.5Bi0.5)TiO3 (NBT) based ceramics has been carried out using X-ray diffraction and scanning electron microscopy (SEM) techniques. Field emission scanning electron microscopy (FE-SEM) images showed that inhibition of grain growth takes place with increasing Cu and Ni concentration. The results indicate that the co-doping of NiO and CuO is effective in improving the dielectric and ferroelectric properties of NBT ceramics. Temperature-dependent dielectric studies have also been carried out at room temperature to 400 °C at different frequencies. The NBT ceramics co-doped with x = 0.06 and y = 0.06 exhibited an excellent dielectric constant ɛr = 1514. The study suggests that there is enormous scope of application of such materials in the future for actuators, ultrasonic transducers and high-frequency piezoelectric devices.

  5. Effects of Lithium Oxide Addition on Sintering Behavior and Electrical Conductivity of Ce0.8Gd0.2O1.9 Ceramics Prepared by Commercial Powders.

    PubMed

    Seo, Seung-Woo; Park, Min-Woo; Lee, Joo-Sin

    2016-05-01

    The densification behavior and electrical conductivity of Ce0.8Gd0.2O1.9 ceramics with lithium oxide concentrations ranging from 0 to 7 mol% were investigated. The sintered density was found to increase with increasing Li2O content up to 2 mol% and then to decrease somewhat upon further Li20 addition. Dense Ce0.8Gd0.2O1.9 ceramics with 97% of the theoretical density could be obtained by sintering the milled mixture with 2 mol% Li2O addition at 1250 degrees C for 5 h. The conductivity of the 2 mol% Li2O-added specimen showed a maximum value of 4.99 x 10(-3) Ω(-1) x cm(-1) at 700 degrees C. Pure Ce0.8Gd0.2O1.9 ceramics needed to be sintered at 1550 degrees C in order to obtain an equivalent theoretical density and conductivity. The addition of Li2O was found to promote the sintering properties and electrical conductivities of Gd2O3-doped CeO2.

  6. Effects of Lithium Oxide Addition on Sintering Behavior and Electrical Conductivity of Ce0.8Gd0.2O1.9 Ceramics Prepared by Commercial Powders.

    PubMed

    Seo, Seung-Woo; Park, Min-Woo; Lee, Joo-Sin

    2016-05-01

    The densification behavior and electrical conductivity of Ce0.8Gd0.2O1.9 ceramics with lithium oxide concentrations ranging from 0 to 7 mol% were investigated. The sintered density was found to increase with increasing Li2O content up to 2 mol% and then to decrease somewhat upon further Li20 addition. Dense Ce0.8Gd0.2O1.9 ceramics with 97% of the theoretical density could be obtained by sintering the milled mixture with 2 mol% Li2O addition at 1250 degrees C for 5 h. The conductivity of the 2 mol% Li2O-added specimen showed a maximum value of 4.99 x 10(-3) Ω(-1) x cm(-1) at 700 degrees C. Pure Ce0.8Gd0.2O1.9 ceramics needed to be sintered at 1550 degrees C in order to obtain an equivalent theoretical density and conductivity. The addition of Li2O was found to promote the sintering properties and electrical conductivities of Gd2O3-doped CeO2. PMID:27483925

  7. Long and short term impacts of CuO, Ag and CeO2 nanoparticles on anaerobic digestion of municipal waste activated sludge.

    PubMed

    Ünşar, E Kökdemir; Çığgın, A S; Erdem, A; Perendeci, N A

    2016-02-01

    In this study, long and short term inhibition impacts of Ag, CuO and CeO2 nanoparticles (NPs) on anaerobic digestion (AD) of waste activated sludge (WAS) were investigated. CuO NPs were detected as the most toxic NPs on AD. As the CuO NP concentration increased from 5 to 1000 mg per gTS, an increase in the inhibition of AD from 5.8 to 84.0% was observed. EC50 values of short and long term inhibitions were calculated as 224.2 mgCuO per gTS and 215.1 mgCuO per gTS, respectively. Ag and CeO2 NPs did not cause drastic impacts on AD as compared to CuO NPs. In the long term test, Ag NPs created 12.1% decrease and CeO2 NPs caused 9.2% increase in the methane production from WAS at the highest dosage. FISH imaging also revealed that the abundance of Archaea in raw WAS was similar in short and long term tests carried out with WAS containing Ag and CeO2 NPs. On the other hand, CuO NPs caused inhibition of Archaea in the long term test. Digestion kinetics of WAS containing Ag, CeO2, CuO NPs were also evaluated with Gompertz, Logistic, Transference and First Order models. The hydrolysis rate constant (kH) for each concentration of Ag and CeO2 NPs and the raw WAS was 0.027745 d(-1) while the kH of WAS containing high concentrations of CuO NPs was found to be 0.001610 d(-1).

  8. Thiolate ligands as a double-edged sword for CO oxidation on CeO2-supported Au25(SR)18 nanoclusters

    SciTech Connect

    Wu, Zili; Jiang, Deen; Mann, Amanda K; Mullins, David R; Qiao, Zhen-an; Allard Jr, Lawrence Frederick; Zeng, Chenjie; Jin, Rongchao; Overbury, Steven {Steve} H

    2014-01-01

    The effect of thiolate ligands was explored on the catalysis of CeO2-rod supported Au25(SR)18 (SR = -SCH2-CH2-Ph) by using CO oxidation as a probe reaction. Reaction kinetic tests, in situ IR and X-ray absorption spectroscopy, and density functional theory (DFT) were employed to understand how the thiolate ligands affect the nature of active sites, activation of CO and O2, as well as the reaction mechanism and kinetics. The intact Au25(SR)18 on CeO2-rod is found not able to adsorb CO. Only when the thiolate ligands are partially removed, starting from the interface between Au25(SR)18 and CeO2 at temperatures of 423 K and above, can the adsorption of CO be observed by IR. DFT calculations suggest that CO adsorbs favorably on the exposed gold atoms. Accordingly, the CO oxidation light-off temperature shifts to lower temperature. Several types of Au sites are probed by IR of CO adsorption during the ligand removal process. The cationic Au sites (charged between 0 and +1) are found to play the major role for low temperature CO oxidation. Similar activation energy and reaction rate are found for CO oxidation on differently treated Au25(SR)18/CeO2-rod, suggesting a simple site-blocking effect of the thiolate ligands in Au nanoclusters catalysis. Isotopic labelling experiments clearly indicate that CO oxidation on Au25(SR)18/CeO2-rod proceeds predominantly via the redox mechanism where CeO2 activates O2 while CO is activated on the de-thiolated gold sites. These results points to a double-edged sword role played by the thiolate ligands on Au25 nanoclusters for CO oxidation.

  9. Low toxicity of HfO2, SiO2, Al2O3 and CeO2 nanoparticles to the yeast, Saccharomyces cerevisiae.

    PubMed

    García-Saucedo, Citlali; Field, James A; Otero-Gonzalez, Lila; Sierra-Álvarez, Reyes

    2011-09-15

    Increasing use of nanomaterials necessitates an improved understanding of their potential impact on environment health. This study evaluated the cytotoxicity of nanosized HfO(2), SiO(2), Al(2)O(3) and CeO(2) towards the eukaryotic model organism Saccharomyces cerevisiae, and characterized their state of dispersion in bioassay medium. Nanotoxicity was assessed by monitoring oxygen consumption in batch cultures and by analysis of cell membrane integrity. CeO(2), Al(2)O(3), and HfO(2) nanoparticles were highly unstable in yeast medium and formed micron-sized, settleable agglomerates. A non-toxic polyacrylate dispersant (Dispex A40) was used to improve nanoparticle stability and determine the impact of enhanced dispersion on toxicity. None of the NPs tested without dispersant inhibited O(2) uptake by yeast at concentrations as high as 1000 mg/L. Dispersant supplementation only enhanced the toxicity of CeO(2) (47% at 1000 mg/L). Dispersed SiO(2) and Al(2)O(3) (1000 mg/L) caused cell membrane damage, whereas dispersed HfO(2) and CeO(2) did not cause significant disruption of membrane integrity at the same concentration. These results suggest that the O(2) uptake inhibition observed with dispersed CeO(2) NPs was not due to reduced cell viability. This is the first study evaluating toxicity of nanoscale HfO(2), SiO(2), Al(2)O(3) and CeO(2) to S. cerevisiae. Overall the results obtained demonstrate that these nanomaterials display low or no toxicity to yeast.

  10. Enhancement of thermoelectric figure of merit by doping Dy in La{sub 0.1}Sr{sub 0.9}TiO{sub 3} ceramic

    SciTech Connect

    Wang, H.C.; Wang, C.L.; Su, W.B.; Liu, J.; Zhao, Y.; Peng, H.; Zhang, J.L.; Zhao, M.L.; Li, J.C.; Yin, N.; Mei, L.M.

    2010-07-15

    Ceramic samples of La{sub 0.1}Sr{sub 0.9-x}Dy{sub x}TiO{sub 3} (x = 0.01, 0.03, 0.07, 0.10) have been prepared by the solid-state reaction method. Characterization from the powder X-ray diffraction indicates that their crystal structure changes from cubic to tetragonal phase. Their electrical and thermal transport properties are measured in the temperature range of 300-1100 K. n-Type thermoelectric is obtained with large Seebeck coefficient. The figure of merit is markedly improved, due to relatively lower electrical resistivity and thermal conductivity by Dy doping effect. A much lower electrical resistivity of 0.8 m{Omega} cm at room temperature is obtained in La{sub 0.1}Sr{sub 0.8}Dy{sub 0.1}TiO{sub 3}, and with a relatively lower thermal conductivity of 2.5 W/m K at 1075 K. The maximum figure of merit reaches {approx}0.36 at 1045 K for La{sub 0.1}Sr{sub 0.83}Dy{sub 0.07}TiO{sub 3}, which is the largest value among n-type oxide thermoelectric ceramics.

  11. Effects of Cr2O3 doping on the microstructure and electrical properties of (Ba,Ca)(Zr,Ti)O3 lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Xia, Xiang; Jiang, Xiangping; Chen, Chao; Jiang, Xingan; Tu, Na; Chen, Yunjing

    2016-06-01

    Lead-free ceramics (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3- x wt.%Cr2O3 (BCZT- xCr) were prepared via the conventional solid-state reaction method. The microstructure and electrical properties of BCZT- xCr samples were systematically studied. XRD and Raman results showed that all samples possessed a single phased perovskite structure and were close to the morphotropic phase boundary (MPB). With the increase of the Cr content, the rhombohedral-tetragonal phase transition temperature ( T R-T) increases slightly, and the Curie temperature ( T C) shifts towards the low temperature side. XPS analysis reveals that Cr3+ and Cr5 + ions co-existed in Cr-doped BCZT ceramics, indicating the different impact on the electrical properties from Cr ions as "acceptor" or "donor". For the x = 0.1 sample, relative high piezoelectric constants d 33 (˜316 pC/N) as well as high Q m (˜554) and low tanδ (˜0.8%) were obtained. In addition, the AC conductivity was also investigated. Hopping charge was considered as the main conduction mechanism at low temperature. As the temperature increases, small polarons and oxygen vacancies conduction played important roles.

  12. Dual-enhancement of ferro-/piezoelectric and photoluminescent performance in Pr{sup 3+} doped (K{sub 0.5}Na{sub 0.5})NbO{sub 3} lead-free ceramics

    SciTech Connect

    Wei, Yongbin; Jia, Yanmin E-mail: ymjia@zjnu.edu.cn; Wu, Jiang; Shen, Yichao; Wu, Zheng E-mail: ymjia@zjnu.edu.cn; Luo, Haosu

    2014-07-28

    A mutual enhancement action between the ferro-/piezoelectric polarization and the photoluminescent performance of rare earth Pr{sup 3+} doped (K{sub 0.5}Na{sub 0.5})NbO{sub 3} (KNN) lead-free ceramics is reported. After Pr{sup 3+} doping, the KNN ceramics exhibit the maximum enhancement of ∼1.2 times in the ferroelectric remanent polarization strength and ∼1.25 times in the piezoelectric coefficient d{sub 33}, respectively. Furthermore, after undergoing a ferro-/piezoelectric polarization treatment, the maximum enhancement of ∼1.3 times in photoluminescence (PL) was observed in the poled 0.3% Pr{sup 3+} doped sample. After the trivalent Pr{sup 3+} unequivalently substituting the univalent (K{sub 0.5}Na{sub 0.5}){sup +}, A-sites ionic vacancies will occur to maintain charge neutrality, which may reduce the inner stress and ease the domain wall motions, yielding to the enhancement in ferro-/piezoelectric performance. The polarization-induced enhancement in PL is attributed to the decrease of crystal symmetry abound the Pr{sup 3+} ions after polarization. The dual-enhancement of the ferro-/piezoelectric and photoluminescent performance makes the Pr{sup 3+} doped KNN ceramic hopeful for piezoelectric/luminescent multifunctional devices.

  13. High temperature dielectric relaxation anomaly of Y³⁺ and Mn²⁺ doped barium strontium titanate ceramics

    SciTech Connect

    Yan, Shiguang; Mao, Chaoliang E-mail: xldong@mail.sic.ac.cn; Wang, Genshui; Yao, Chunhua; Cao, Fei; Dong, Xianlin E-mail: xldong@mail.sic.ac.cn

    2014-10-14

    Relaxation like dielectric anomaly is observed in Y³⁺ and Mn²⁺ doped barium strontium titanate ceramics when the temperature is over 450 K. Apart from the conventional dielectric relaxation analysis method with Debye or modified Debye equations, which is hard to give exact temperature dependence of the relaxation process, dielectric response in the form of complex impedance, assisted with Cole-Cole impedance model corrected equivalent circuits, is adopted to solve this problem and chase the polarization mechanism in this paper. Through this method, an excellent description to temperature dependence of the dielectric relaxation anomaly and its dominated factors are achieved. Further analysis reveals that the exponential decay of the Cole distribution parameter n with temperature is confirmed to be induced by the microscopic lattice distortion due to ions doping and the interaction between the defects. At last, a clear sight to polarization mechanism containing both the intrinsic dipolar polarization and extrinsic distributed oxygen vacancies hopping response under different temperature is obtained.

  14. Characterization and thermal shock behavior of composite ceramic coating doped with ZrO2 particles on TC4 by micro-arc oxidation

    NASA Astrophysics Data System (ADS)

    Zhong, Yesheng; Shi, Liping; Li, Mingwei; He, Fei; He, Xiaodong

    2014-08-01

    A kind of composite ceramic coating was prepared on the surface of Ti-6Al-4V alloy to improve its thermal shock resistance by micro-arc oxidation method in a NaAlO2 and NaH2PO2 solution doped with ZrO2 micro-particles. Phase structure of the MAO coatings was studied by XRD techniques. The main crystal phases of the composite coating were Al2TiO5, rutile TiO2 and ZrO2, no corundum phase, α-alumina and γ-alumina. SEM investigations revealed that in Al-P MAO coating a volcano top-like pore surface was exhibited, while for Al-P-Zr MAO coating only few pores and island-like melting oxidation with different sized around the volcano. The presence of doped ZrO2 particles was beneficial to the growth of the coatings, but not good for surface toughness. Thermal shock resistant property was tested using the home-made thermal shock testing device. The thermal shock results indicated that no cracks occurred on the surface and no peeling phenomenon happened on the interface bonding zone after 50 cycles under temperature drop of 980 °C. A thermal shock mechanism was proposed based on the microstructure and good metallurgical bond strength of membrane-based interface as well.

  15. Sol-Gel Derived Mg-Based Ceramic Scaffolds Doped with Zinc or Copper Ions: Preliminary Results on Their Synthesis, Characterization, and Biocompatibility.

    PubMed

    Theodorou, Georgios S; Kontonasaki, Eleana; Theocharidou, Anna; Bakopoulou, Athina; Bousnaki, Maria; Hadjichristou, Christina; Papachristou, Eleni; Papadopoulou, Lambrini; Kantiranis, Nikolaos A; Chrissafis, Konstantinos; Paraskevopoulos, Konstantinos M; Koidis, Petros T

    2016-01-01

    Glass-ceramic scaffolds containing Mg have shown recently the potential to enhance the proliferation, differentiation, and biomineralization of stem cells in vitro, property that makes them promising candidates for dental tissue regeneration. An additional property of a scaffold aimed at dental tissue regeneration is to protect the regeneration process against oral bacteria penetration. In this respect, novel bioactive scaffolds containing Mg(2+) and Cu(2+) or Zn(2+), ions known for their antimicrobial properties, were synthesized by the foam replica technique and tested regarding their bioactive response in SBF, mechanical properties, degradation, and porosity. Finally their ability to support the attachment and long-term proliferation of Dental Pulp Stem Cells (DPSCs) was also evaluated. The results showed that conversely to their bioactive response in SBF solution, Zn-doped scaffolds proved to respond adequately regarding their mechanical strength and to be efficient regarding their biological response, in comparison to Cu-doped scaffolds, which makes them promising candidates for targeted dental stem cell odontogenic differentiation and calcified dental tissue engineering. PMID:26981124

  16. Sol-Gel Derived Mg-Based Ceramic Scaffolds Doped with Zinc or Copper Ions: Preliminary Results on Their Synthesis, Characterization, and Biocompatibility

    PubMed Central

    Theodorou, Georgios S.; Kontonasaki, Eleana; Theocharidou, Anna; Bakopoulou, Athina; Bousnaki, Maria; Hadjichristou, Christina; Papachristou, Eleni; Papadopoulou, Lambrini; Kantiranis, Nikolaos A.; Chrissafis, Konstantinos; Paraskevopoulos, Konstantinos M.; Koidis, Petros T.

    2016-01-01

    Glass-ceramic scaffolds containing Mg have shown recently the potential to enhance the proliferation, differentiation, and biomineralization of stem cells in vitro, property that makes them promising candidates for dental tissue regeneration. An additional property of a scaffold aimed at dental tissue regeneration is to protect the regeneration process against oral bacteria penetration. In this respect, novel bioactive scaffolds containing Mg2+ and Cu2+ or Zn2+, ions known for their antimicrobial properties, were synthesized by the foam replica technique and tested regarding their bioactive response in SBF, mechanical properties, degradation, and porosity. Finally their ability to support the attachment and long-term proliferation of Dental Pulp Stem Cells (DPSCs) was also evaluated. The results showed that conversely to their bioactive response in SBF solution, Zn-doped scaffolds proved to respond adequately regarding their mechanical strength and to be efficient regarding their biological response, in comparison to Cu-doped scaffolds, which makes them promising candidates for targeted dental stem cell odontogenic differentiation and calcified dental tissue engineering. PMID:26981124

  17. Role of Mn doping for obtaining of hexagonal phase in Ba0.98Zn0.02TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Das, S. K.; Roul, B. K.

    2016-08-01

    This paper reports the observation of hexagonal phase of barium titanate by Mn doping and its effect on dielectric and magnetic properties. Ceramic samples of Ba0.98Zn0.02Ti1-xMnxO3 (where, x= 0.04, 0.06 and 0.08) were prepared by traditional solid-state reaction route. The hexagonal phase is stabilized in the composition Ba0.98Zn0.02Ti0.92Mn0.08O3 and a very feeble M-H loop is also observed in that composition. This induced magnetism is expected due to the exchange interactions between magnetic polarons formed by oxygen vacancies with Mn ions. The dielectric constant as well as the ferroelectric to paraelectric transition temperature is systematically decreased with increasing of Mn doping concentration. Further to that, the temperature dependent dielectric constant curve is also broadened at transition temperature with increasing of Mn concentration. However, the ferroelectric to paraelectric transition temperature is well above room temperature.

  18. Transparent oxyfluoride glass ceramics co-doped with Er{sup 3+} and Yb{sup 3+} - Crystallization and upconversion spectroscopy

    SciTech Connect

    Gugov, I.; Mueller, M.; Ruessel, C.

    2011-05-15

    Transparent glass ceramics in the system SiO{sub 2}-B{sub 2}O{sub 3}-PbO-CdO-PbF{sub 2}-CdF{sub 2}-YbF{sub 3}-ErF{sub 3} showing infrared to visible anti-Stokes (upconversion) luminescence are studied in the present work. The glass compositions have been optimized in order to reduce the melting temperature and, hence, to obtain laboratory scale samples with good optical quality. Erbium-doped nanoscale Pb{sub 4}Yb{sub 3}F{sub 17} crystals are precipitated in the precursor glasses during annealing at temperatures 30-40 K above T{sub g}. A kinetically self-constrained growth explains the nano sizes of the crystals. Both the Stokes and anti-Stokes luminescence spectra of glasses could be explained with clustering of the Yb{sup 3+} and Er{sup 3+} ions in fluorine-rich regions. At the annealing temperature these regions act as nucleation precursors. The crystal growth further enhances the local concentration of these ions. Consequently, a series of energy transfer and energy cross relaxation processes occurs between adjacent rare earth ions leading to the observed luminescence spectra of the glass ceramics studied. -- Graphical abstract: A highly viscous shell (shown in the picture in dark blue) is build around the growing crystal (white circles). When the shell's T{sub g} approaches the annealing temperature, the crystal growth is fully suppressed for kinetic reasons. The upconversion luminescence, resulting from the simultaneous absorption of two and even three infrared photons, is depicted schematically in the right part of the figure. Display Omitted Highlights: {yields} New oxyfluoride glass compositions with reduced melting temperature are formulated. {yields} The phase Pb{sub 4}Yb{sub 3}F{sub 17} doped with Er{sup 3+} ions crystallizes in these glasses. {yields} A kinetically self-constrained growth explains the nano sizes of the crystals. {yields} Clustering of Yb{sup 3+}, Er{sup 3+} and Pb{sup 2+} ions into fluorine-rich glass regions is observed. {yields} The

  19. Evaluation of chemical stability, thermal expansion coefficient, and electrical properties of solid state and wet-chemical synthesized Y and Mn-codoped CeO2 for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Handal, Hala T.; Thangadurai, Venkataraman

    2013-12-01

    Chemical stability and high electrical conductivity under the operating conditions of solid oxide fuel cell (SOFC) are considered as the momentum for innovating solid electrolytes and electrodes. In this paper, we report synthesis, structure, chemical stability and electrical conductivity of novel co-doped Ce0.9-xY0.1MnxO2-δ (x = 0-15 mol%) (CYMO). X-ray diffraction of Mn and Y-doped CeO2 shows the formation of fluorite-type structure with a space group Fm-3m. A few weak peaks corresponding to a tetragonal Mn3O4 phase has been detected in some samples. Solubility of Mn in ceria is explained by considering the influence of the ionic radius, the crystal structure and its electronic structure. Thermal analysis shows dissimilarity between the reduction behavior of Ce0.9Mn0.1O2-δ and Ce0.9-xY0.1MnxO2-δ. Ce0.8Y0.1Mn0.1O2-δ exhibited the highest conductivity of ˜6 × 10-2 S cm-1 and 0.15 S cm-1 at 700 °C in air and H2, respectively. Surface studies have confirmed the formation of S species upon exposure to 30 ppm H2S in H2 and a mechanism for S poisoning is presented.

  20. Promoting Effect of CeO2 in the Electrocatalytic Activity of Rhodium for Ethanol Electro-Oxidation

    SciTech Connect

    He, Q.; Mukerjee, S; Shyam, B; Ramaker, D; Parres-Esclapex, D; Illan-Gomez, M; Bueno-Lopez, A

    2009-01-01

    The promoting effect of ceria in the electrocatalytic activity of rhodium for ethanol electro-oxidation in alkali media has been studied. Rh/C, CeO2/C and RhCeO2/C catalysts were synthesized and characterized by TEM, XRD, XPS, TG-MS, H2-TPR and XAS. The electrocatalytic activity was studied by Cyclic Voltammetry (CV) and chronoamperometry. The onset potential of oxidation on RhCeO2/C was shifted negatively as compared to that on Rh/C, despite ceria itself does not show any electrocatalytic activity. The promoting effect of ceria has been attributed to the improved rhodium dispersion, and differences in the oxidation state of rhodium between Rh/C and RhCeO2/C were not found. The carbon support reduces rhodium species to Rh0, and also partially reduces ceria, during the samples preparation, and the surface of the carbon support is oxidised.

  1. Coadsorbed species explain the mechanism of methanol temperature-desorption on CeO2(111)

    DOE PAGESBeta

    Sutton, Jonathan E.; Steven H. Overbury; Beste, Ariana

    2016-03-24

    Here, we have used density functional theory calculations to investigate the temperature-programmed desorption (TPD) of methanol from CeO2(111). For the first time, low-temperature water formation and high-temperature methanol desorption are explained by our calculations. High coverages of methanol, which correspond to experimental conditions, are required to properly describe these features of the TPD spectrum. We identify a mechanism for the low-temperature formation of water involving the dissociation of two methanol molecules on the same surface O atom and filling of the resulting surface vacancy with one of the methoxy products. After water desorption, methoxy groups are stabilized on the surfacemore » and react at higher temperatures to form methanol and formaldehyde by a disproportionation mechanism. Alternatively, the stabilized methoxy groups undergo sequential C–H scission reactions to produce formaldehyde. Calculated energy requirements and methanol/formaldehyde selectivity agree with the experimental data.« less

  2. Comparison of the high-pressure behavior of the cerium oxides Ce2O3 and CeO2

    DOE PAGESBeta

    Lipp, M. J.; Jeffries, J. R.; Cynn, H.; Park Klepeis, J. -H.; Evans, W. J.; Mortensen, D. R.; Seidler, G. T.; Xiao, Y.; Chow, P.

    2016-02-09

    We studied the high-pressure behavior of Ce2O3 using angle-dispersive x-ray diffraction to 70 GPa and compared with that of CeO2. Up to the highest pressure Ce2O3 remains in the hexagonal phase (space group 164, P ¯32/m1) typical for the lanthanide sesquioxides. We did not observe a theoretically predicted phase instability for 30 GPa. The isothermal bulk modulus and its pressure derivative for the quasihydrostatic case are B0 = 111 ± 2 GPa, B'0 = 4.7 ± 0.3, and for the case without pressure-transmitting medium B0 = 104 ±4 GPa, B'0 = 6.5 ± 0.4. Starting from ambient-pressure magnetic susceptibility measurementsmore » for both oxides in highly purified form,we find that the Ce atom in Ce2O3 behaves like a trivalent Ce3+ ion (2.57μB per Ce atom) in contrast to previously published data. Since x-ray emission spectroscopy of the Lγ (4d3/2 → 2p1/2) transition is sensitive to the 4f -electron occupancy, we also followed the high-pressure dependence of this line for both oxides up to 50 GPa. We observed no change of the respective line shape, indicating that the 4f -electron configuration is stable for both materials. We posit from this data that the 4f electrons do not drive the volume collapse of CeO2 from the high-symmetry, low-pressure fluorite structure to the lower-symmetry orthorhombic phase.« less

  3. Voltage tunable dielectric properties of oxides at nanoscale: TiO2 and CeO2 as model systems

    NASA Astrophysics Data System (ADS)

    Prakash, T.; Tamil Selvan, A.; Suraiya Begum, S. N.

    2016-03-01

    Carrier transport through electrically active grain boundaries has been studied under biased condition using Solartron 1260 impedance/gain phase analyzer with an applied AC potential of 250 mV in the frequency range 1 Hz-1 MHz for nanocrystalline TiO2 and CeO2 as the model systems. Prior to the measurement both the materials were converted into cylindrical pellets with (8 mm diameter and 1 mm thick) by applying uni-axial pressure of 4 ton using a hydraulic press, then sintered at 300, 450 and 600 °C for 30 min for TiO2 sample and for the case of CeO2 it was done at 300, 600 and 900 °C for 30 min. Further, they were characterized using powder X-ray diffractometer (XRD) and transmission electron microscopy (TEM) to know the crystal structure, average crystallite size and morphology. The impedance measurements were performed at room temperature under applied DC bias voltages from 0 to 3 V in the periodic increment of 0.2 V. The observed applied bias voltage effect on dielectric constant of both the systems was analyzed with 'grain boundary double Schottky potential barrier height model' for different grain sizes. The percentage of voltage tunable dielectric constant (T%) as a function of frequency was estimated for all the grain sizes and it was found to be increase with reduction of grain size. Our experimental findings reveal the possibilities of utilizing these nanocrystals as a potential active material for phased array antenna since both the samples exhibits T% = 85% at 100 Hz frequency.

  4. Structure, magnetic, and dielectric properties of Ti-doped LaFeO{sub 3} ceramics synthesized by polymer pyrolysis method

    SciTech Connect

    Phokha, Sumalin; Hunpratup, Sitchai; Pinitsoontorn, Supree; Putasaeng, Bundit; Rujirawat, Saroj; Maensiri, Santi

    2015-07-15

    Highlights: • The LaFe{sub 1−x}Ti{sub x}O{sub 3} samples can be successfully prepared by polymer pyrolysis method. • XANES spectra confirmed the mixed valence states of Fe{sup 3+} and Fe{sup 4+} for Fe ions and valence states of Ti{sup 4+} for Ti ions. • The ferromagnetism (FM) at room temperature (RT) can be observed in all LaFe{sub 1−x}Ti{sub x}O{sub 3} nanoparticles and ceramics. • The uncompensated spins at the surface played an important role in the magnetism of LaFe{sub 1−x}Ti{sub x}O{sub 3} nanoparticles. • The giant dielectric behavior of the ceramic samples can be easily found by substitution at B site. - Abstract: Perovskite Ti-doped LaFeO{sub 3} (LaFe{sub 1−x}Ti{sub x}O{sub 3}, x = 0, 0.1, and 0.2) nanoparticles synthesized by the polymer pyrolysis method were investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray absorption near edge spectroscopy (XANES), and vibrating sample magnetometry (VSM) were used to characterize phase, morphology, valence states and magnetic properties of the samples. The samples had a phase of the orthorhombic structure with crystallite sizes of 25 ± 2–47 ± 2 nm for nanoparticles, while ceramic samples had the grain sizes of 0.9 ± 0.3–6.0 ± 2.3 μm. The result of XANES spectra showed that the Fe{sup 3+}/Fe{sup 4+} and Ti{sup 4+} exist in the samples. The weak ferromagnetic behavior at room temperature is observed for all LaFe{sub 1−x}Ti{sub x}O{sub 3} samples with a maximum magnetization of 0.32 emu/g for x = 0.2. Additionally, larger hysteresis loops induced significantly in ceramic samples with no saturation up to 10 kOe. The dielectric properties as a function of frequency at low temperatures suggest the presence of polarization in the samples due to the electron hopping between Fe{sup 3+} and Fe{sup 4+} ions.

  5. Stability of uncoated and fulvic acids coated manufactured CeO2 nanoparticles in various conditions: From ultrapure to natural Lake Geneva waters.

    PubMed

    Oriekhova, Olena; Stoll, Serge

    2016-08-15

    Understanding the behavior of engineered nanoparticles in natural water and impact of water composition in changing conditions is of high importance to predict their fate once released into the environment. In this study we investigated the stability of uncoated and Suwannee River fulvic acids coated CeO2 manufactured nanoparticles in various environmental conditions. The effect of pH changes on the nanoparticle and coating stability was first studied in ultrapure water as well as the variation of zeta potentials and sizes with time in presence of fulvic acids at environmental pH. Then the stability of CeO2 in synthetic and natural Lake Geneva waters was investigated as a function of fulvic acids concentration. Our results indicate that the adsorption of environmentally relevant concentrations of Suwannee River fulvic acids promotes CeO2 stabilization in ultrapure water as well as synthetic water and that the coating stability is high upon pH variations. On the other hand in natural Lake Geneva water CeO2 NPs are found in all cases aggregated due to the effect of heterogeneous organic and inorganic compounds.

  6. Pressure Regulations on the Surface Properties of CeO2 Nanorods and Their Catalytic Activity for CO Oxidation and Nitrile Hydrolysis Reactions.

    PubMed

    Li, Jing; Zhang, Zhiyun; Gao, Wei; Zhang, Sai; Ma, Yuanyuan; Qu, Yongquan

    2016-09-01

    Surface properties of nanoscale CeO2 catalysts in terms of the surface Ce(3+) fraction and concentration of oxygen vacancy can affect their catalytic performance significantly. Continual adjustment on surface properties of CeO2 with the morphological preservation has not been realized by synthetic methods. The revisited studies show that surface properties of CeO2 nanorods can be effectively regulated by synthetic pressures while the rodlike morphology is well-preserved. Such phenomena are ascribed to the contact possibility between Ce(3+) species and dissolved O2, which is balanced by the rapidly increased and gradually saturated dissolution/recrystallization rate of Ce(OH)3 and linearly increased concentration of dissolved O2 with the increase of total air pressure or partial pressure of O2. Surface-property-dependent catalytic activity of CeO2 nanorods synthesized under various pressures was also demonstrated in two benchmark reactions-catalytic oxidation of CO and hydrolysis of nitrile. Such a finding of the pressure regulation on the reducible metal oxides provides an effective approach to rationally design novel catalysts for specific reactions, where ceria are supports, promoters, or actives.

  7. Bioavailability of CeO2 and SnO2 nanoparticles evaluated by dietary uptake in the earthworm Eisenia fetida and sequential extraction of soil and feed.

    PubMed

    Carbone, Serena; Hertel-Aas, Turid; Joner, Erik J; Oughton, Deborah H

    2016-11-01

    The growing number of nanotechnology products on the market will inevitably lead to the release of engineered nanomaterials with potential risk to humans and environment. This study set out to investigate the exposure of soil biota to engineered nanoparticles (NPs). Cerium dioxide (CeO2 NPs) and tin dioxide nanoparticles (SnO2 NPs) were radiolabelled using neutron activation, and employed to assess the uptake and excretion kinetics in the earthworm Eisenia fetida. Through sequential extraction, NPs bioavailability in two contrasting soils and in earthworm feed was also investigated. Neither CeO2 NPs nor SnO2 NPs bioaccumulated in earthworms, and both were rapidly excreted when worms were transferred to clean soil. Low bioavailability was also indicated by low amounts of NPs recovered during extraction with non-stringent extractants. CeO2 NPs showed increasing mobility in organic soil over time (28 days), indicating that organic matter has a strong influence on the fate of CeO2 NPs in soil.

  8. Hydrophilic CeO2 nanocubes protect pancreatic β-cell line INS-1 from H2O2-induced oxidative stress.

    PubMed

    Lyu, Guang-Ming; Wang, Yan-Jie; Huang, Xue; Zhang, Huai-Yuan; Sun, Ling-Dong; Liu, Yan-Jun; Yan, Chun-Hua

    2016-04-21

    Oxidative stress plays a key role in the occurrence and development of diabetes. With their unique redox properties, CeO2 nanoparticles (nanoceria) exhibit promising potential for the treatment of diabetes resulting from oxidative stress. Here, we develop a novel preparation of hydrophilic CeO2 nanocubes (NCs) with two different sizes (5 nm and 25 nm) via an acetate assisted hydrothermal method. Dynamic light scattering, zeta potential measurements and thermogravimetric analyses were utilized to investigate the changes in the physico-chemical characteristics of CeO2 NCs when exposed to in vitro cell culture conditions. CCK-8 assays revealed that the CeO2 NCs did not impair cell proliferation in the pancreatic β-cell line INS-1 at the highest dose of 200 μg mL(-1) over the time scale of 72 h, while being able to protect INS-1 cells from H2O2-induced cytotoxicity even after protein adsorption. It is also noteworthy that nanoceria with a smaller hydrodynamic radius exhibit stronger antioxidant and anti-apoptotic effects, which is consistent with their H2O2 quenching capability in biological systems. These findings suggest that nanoceria can be used as an excellent antioxidant for controlling oxidative stress-induced pancreatic β-cell damage.

  9. Evidence of the differential biotransformation and genotoxicity of ZnO and CeO2 nanoparticles on soybean (Glycine max) plants

    PubMed Central

    López-Moreno, Martha L.; de la Rosa, Guadalupe; Hernández-Viezcas, José Á.; Castillo-Michel, Hiram; Botez, Cristian E.; Peralta-Videa, José R.; Gardea-Torresdey, Jorge L.

    2010-01-01

    Concern and interest related to the effects of nanomaterials on living organisms are growing in both the scientific and public communities. Reports have described the toxicity of nanoparticles (NPs) on micro and macro organisms, including some plant species. Nevertheless, to the authors’ knowledge there are no reports on the biotransformation of NPs by edible terrestrial plants. Here, shown for the first time, is evidence pertaining to the biotransformation of ZnO and CeO2 NPs in plant seedlings. Although the NPs did not affect soybean germination, they produced a differential effect on plant growth and element uptake. By using synchrotron X-ray absorption spectroscopy we obtained clear evidence of the presence of CeO2 NPs in roots, whereas ZnO NPs were not present. Random amplified polymorphic DNA assay was applied to detect DNA damage and mutations caused by NPs. Results obtained from the exposure of soybean plants to CeO2 NPs show the appearance of four new bands at 2000 mg L−1 and three new bands at 4000 mg L−1 treatment. In this study we demonstrated genotoxic effects from the exposure of soybean plants to CeO2 NPs. PMID:20384348

  10. Effect of Nano CeO2 Addition on the Microstructure and Properties of a Cu-Al-Ni Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Pandey, Abhishek; Jain, Ashish Kumar; Hussain, Shahadat; Sampath, V.; Dasgupta, Rupa

    2016-08-01

    This article deals with the effect of adding nano CeO2 to act as a grain pinner/refiner to a known Cu-Al-Ni shape memory alloy. Elements were taken in a predefined ratio to prepare 300 g alloy per batch and melted in an induction furnace. Casting was followed by homogenization at 1173 K (900 °C) and rolling to make sheets of 0.5-mm thickness. Further, samples were characterized for microstructure using optical and electron microscope, hardness, and different phase studies by X-ray and transformation temperatures by differential scanning calorimetry. X-ray peak broadenings and changes were investigated to estimate the crystallite size, lattice strain, and phase changes due to different processing steps. A nearly uniform distribution of CeO2 and better martensitic structure were observed with increasing CeO2. The addition of CeO2 also shows a visible effect on the transformation temperature and phase formation.

  11. Germination and early plant development of 10 plant species exposed to Nano TiO2 and CeO2

    EPA Science Inventory

    Ten agronomic plant species were exposed to different concentrations of nano-TiO2 or CeO2 (0, 250, 500 and 1000 ug/l) and followed to examine effects on germination and early seedling development. For TiO2, cabbage showed increased and corn decreased percent germination, while ...

  12. WO3/CeO2/TiO2 Catalysts for Selective Catalytic Reduction of NO(x) by NH3: Effect of the Synthesis Method.

    PubMed

    Michalow-Mauke, Katarzyna A; Lu, Ye; Ferri, Davide; Graule, Thomas; Kowalski, Kazimierz; Elsener, Martin; Kröcher, Oliver

    2015-01-01

    WO3/CeO2/TiO2, CeO2/TiO2 and WO3/TiO2 catalysts were prepared by wet impregnation. CeO2/TiO2 and WO3/TiO2 showed activity towards the selective catalytic reduction (SCR) of NO(x) by NH3, which was significantly improved by subsequent impregnation of CeO/TiO2 with WO3. Catalytic performance, NH3 oxidation and NH3 temperature programmed desorption of wet-impregnated WO3/CeO2/TiO2 were compared to those of a flame-made counterpart. The flame-made catalyst exhibits a peculiar arrangement of W-Ce-Ti-oxides that makes it very active for NH3-SCR. Catalysts prepared by wet impregnation with the aim to mimic the structure of the flame-made catalyst were not able to fully reproduce its activity. The differences in the catalytic performance between the investigated catalysts were related to their structural properties and the different interaction of the catalyst components.

  13. Controlled synthesis of CeO2 microstructures from 1D rod-like to 3D lotus-like and their morphology-dependent properties

    NASA Astrophysics Data System (ADS)

    Gong, Jinfeng; Meng, Fanming; Fan, Zhenghua; Li, Huijie

    2016-10-01

    Monodisperse 3D lotus-like CeO2 microstructures have been successfully synthesized via controlling the morphology of CeCO3OH precursors under hydrothermal condition as well as subsequent calcination. The reaction time was systematically investigated. XRD, FT-IR, SEM, TEM, XPS, Raman scattering and Photoluminescence (PL) spectra were employed to characterize the samples. The lotus-like CeO2 hierarchical structures with an average of 4-6 μm are composed of many nanoplates of 100-200 nm in thickness as the petals stacking together to form open flowers and have a fluorite cubic structure. Based on the time-dependent morphology evolution evidences, a nucleation-dissolution-recrystallization mechanism has been proposed to explain the transformation from rod-like structures to lotus-like CeO2 hierarchical structures with the increase of reaction time. It is found that there are Ce3+ ions and oxygen vacancies in surface of samples. The magnetic and photoluminescence measurements indicated that all CeO2 samples exhibit excellent ferromagnetism and optical properties at room temperature, and while increasing the reaction time, the ferromagnetism and optical properties increase more, which can be reasonably explained for the influences of the different morphology of the particles and the concentration of oxygen vacancies and Ce3+ ions. [Figure not available: see fulltext.

  14. Pressure Regulations on the Surface Properties of CeO2 Nanorods and Their Catalytic Activity for CO Oxidation and Nitrile Hydrolysis Reactions.

    PubMed

    Li, Jing; Zhang, Zhiyun; Gao, Wei; Zhang, Sai; Ma, Yuanyuan; Qu, Yongquan

    2016-09-01

    Surface properties of nanoscale CeO2 catalysts in terms of the surface Ce(3+) fraction and concentration of oxygen vacancy can affect their catalytic performance significantly. Continual adjustment on surface properties of CeO2 with the morphological preservation has not been realized by synthetic methods. The revisited studies show that surface properties of CeO2 nanorods can be effectively regulated by synthetic pressures while the rodlike morphology is well-preserved. Such phenomena are ascribed to the contact possibility between Ce(3+) species and dissolved O2, which is balanced by the rapidly increased and gradually saturated dissolution/recrystallization rate of Ce(OH)3 and linearly increased concentration of dissolved O2 with the increase of total air pressure or partial pressure of O2. Surface-property-dependent catalytic activity of CeO2 nanorods synthesized under various pressures was also demonstrated in two benchmark reactions-catalytic oxidation of CO and hydrolysis of nitrile. Such a finding of the pressure regulation on the reducible metal oxides provides an effective approach to rationally design novel catalysts for specific reactions, where ceria are supports, promoters, or actives. PMID:27534804

  15. Bioavailability of CeO2 and SnO2 nanoparticles evaluated by dietary uptake in the earthworm Eisenia fetida and sequential extraction of soil and feed.

    PubMed

    Carbone, Serena; Hertel-Aas, Turid; Joner, Erik J; Oughton, Deborah H

    2016-11-01

    The growing number of nanotechnology products on the market will inevitably lead to the release of engineered nanomaterials with potential risk to humans and environment. This study set out to investigate the exposure of soil biota to engineered nanoparticles (NPs). Cerium dioxide (CeO2 NPs) and tin dioxide nanoparticles (SnO2 NPs) were radiolabelled using neutron activation, and employed to assess the uptake and excretion kinetics in the earthworm Eisenia fetida. Through sequential extraction, NPs bioavailability in two contrasting soils and in earthworm feed was also investigated. Neither CeO2 NPs nor SnO2 NPs bioaccumulated in earthworms, and both were rapidly excreted when worms were transferred to clean soil. Low bioavailability was also indicated by low amounts of NPs recovered during extraction with non-stringent extractants. CeO2 NPs showed increasing mobility in organic soil over time (28 days), indicating that organic matter has a strong influence on the fate of CeO2 NPs in soil. PMID:27474912

  16. CO, CO2 and H2 adsorption on ZnO, CeO2, and ZnO/CeO2 surfaces: DFT simulations.

    PubMed

    Reimers, Walter G; Baltanás, Miguel A; Branda, María M

    2014-06-01

    The adsorption of the molecules CO, CO2, and H2 on several ceria and zinc oxide surfaces was studied by means of periodical DFT calculations and compared with infrared frequency data. The stable CeO2(111), CeO2(331), and ZnO(0001) perfect faces were the first substrates considered. Afterwards, the same surfaces with oxygen vacancies and a ZnO monolayer grown on Ceria(111) were also studied in order to compare the behaviors and reactivities of the molecules at those surfaces. The ceria surfaces were substantially more reactive than the ZnO surface towards the CO2 molecule. The highest adsorption energy for this molecule was obtained on the CeO2(111) surface with oxygen vacancies. The molecules CO and H2 both presented low or very low reactivities on all of the surfaces studied, although some reactivity was observed for the adsorption of CO onto the surfaces with oxygen vacancies, whereas H2 exhibited reactivity towards the CeO2(111) surface with oxygen vacancies. This work was performed to provide a firm foundation for novel process development in methanol synthesis from carbon oxides, steam reforming of methanol for hydrogen production, and/or the water-gas shift reaction. PMID:24903980

  17. Differential genomic effects on canonical signaling pathways by two different CeO2 nanoparticles in HepG2 cells

    EPA Science Inventory

    Differential genomic effects on signaling pathways by two different CeO2 nanoparticles in HepG2 cells. Sheau-Fung Thai1, Kathleen A. Wallace1, Carlton P. Jones1, Hongzu Ren2, Benjamin T. Castellon1, James Crooks2, Kirk T. Kitchin1. 1Integrated Systems Toxicology Divison, 2Resea...

  18. Mixed-valence metal oxide nanoparticles as electrochemical half-cells: substituting the Ag/AgCl of reference electrodes by CeO(2-x) nanoparticles.

    PubMed

    Nagarale, Rajaram K; Hoss, Udo; Heller, Adam

    2012-12-26

    Cations of mixed valence at surfaces of metal oxide nanoparticles constitute electrochemical half-cells, with potentials intermediate between those of the dissolved cations and those in the solid. When only cations at surfaces of the particles are electrochemically active, the ratio of electrochemically active/all cations is ~0.1 for 15 nm diameter CeO(2-x) particles. CeO(2-x) nanoparticle-loaded hydrogel films on printed carbon and on sputtered gold constitute reference electrodes having a redox potential similar to that of Ag/AgCl in physiological (0.14 M) saline solutions. In vitro the characteristics of potentially subcutaneously implantable glucose monitoring sensors made with CeO(2-x) nanoparticle reference electrodes are undistinguishable from those of sensors made with Ag/AgCl reference electrodes. Cerium is 900 times more abundant than silver, and commercially produced CeO(2-x) nanoparticle solutions are available at prices well below those of the Ag/AgCl pastes used in the annual manufacture of ~10(9) reference electrodes of glucose monitoring strips for diabetes management. PMID:23171288

  19. Dissolved cerium contributes to uptake of Ce in the presence of differently sized CeO2-nanoparticles by three crop plants.

    PubMed

    Schwabe, Franziska; Tanner, Simon; Schulin, Rainer; Rotzetter, Aline; Stark, Wendelin; von Quadt, Albrecht; Nowack, Bernd

    2015-03-01

    We investigated the uptake of cerium (Ce) dioxide nanoparticles (NPs) by hydroponically grown wheat, pumpkin and sunflower plants. The presence of plant roots in nutrient solution led to a substantial increase in the dissolution of CeO2-NP compared to plant-free medium. Experiments with Zr/CeOx-NP revealed that Ce was not only taken up in the form of NPs, but simultaneously to a significant degree also as dissolved Ce(iii) ions, which then re-precipitated in the form of CeO2-NPs inside the leaves. The contribution of dissolved Ce uptake was particularly large for particles smaller than 10 nm due to their higher dissolution rate. Our data also indicate that the translocation of Ce resulting from NP-root-exposure is species dependent. When Ce was supplied as dissolved ions, sunflower had the highest capacity of Ce-ion accumulation inside the leaves, while there was no significant difference between pumpkin and wheat. We found no Ce translocation from roots into shoots when only NPs bigger than 20 nm were applied. This study highlights that plant root activity can have a significant impact on the dissolution of CeO2-NPs in soil solution and that uptake of dissolved Ce(iii) followed by re-precipitation needs to be considered as an important pathway in studies of CeO2-NP uptake by plants. PMID:25634091

  20. Colloidal stability of CeO2 nanoparticles coated with either natural organic matter or organic polymers under various hydrochemical conditions

    NASA Astrophysics Data System (ADS)

    Dippon, Urs; Pabst, Silke; Klitzke, Sondra

    2016-04-01

    The worldwide marked for engineered nanoparticles (ENPs) is growing and concerns on the environmental fate- and toxicity of ENPs are rising. Understanding the transport of ENPs within and between environmental compartments such as surface water and groundwater is crucial for exposition modeling, risk assessment and ultimately the protection of drinking water resources. The transport of ENPs is strongly influenced by the surface properties and aggregation behavior of the particles, which is strongly controlled by synthetic and natural organic coatings. Both, surface properties and aggregation characteristics are also key properties for the industrial application of ENPs, which leads to the development and commercialization of an increasing number of surface-functionalized ENPs. These include metals and oxides such as Cerium dioxide (CeO2) with various organic coatings. Therefore, we investigate CeO2 ENPs with different surface coatings such as weakly anionic polyvinyl alcohol (PVA) or strongly anionic poly acrylic acid (PAA) with respect to their colloidal stability in aqueous matrix under various hydrochemical conditions (pH, ionic strength) and their transport behavior in sand filter columns. Furthermore, we investigate the interaction of naturally occurring organic matter (NOM) with CeO2 ENPs and its effect on surface charge (zeta potential), colloidal stability and transport. While uncoated CeO2 ENPs aggregate at pH > 4 in aqueous matrix, our results show that PAA and PVA surface coatings as well as NOM sorbed to CeO2-NP surfaces can stabilize CeO2 ENPs under neutral and alkaline pH conditions in 1 mM KCl solution. Under slightly acidic conditions, differences between the three particle types were observed. PVA can stabilize particle suspensions in presence of 1 mM KCl at pH > 4.3, PAA at pH >4.0 and NOM at >3.2. While the presence of KCl did not influence particle size of NOM-CeO2 ENPs, CaCl2 at >2 mM lead to aggregation. Further results on the influence of KCl and CaCl2 on aggregation of coated CeO2 ENPs and transport in sand filter columns will be presented.