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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. 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

  4. 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

  5. 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.

  6. A dipole polarizable potential for reduced and doped CeO(2) obtained from first principles.

    PubMed

    Burbano, Mario; Marrocchelli, Dario; Yildiz, Bilge; Tuller, Harry L; Norberg, Stefan T; Hull, Stephen; Madden, Paul A; Watson, Graeme W

    2011-06-29

    In this paper we present the parameterization of a new interionic potential for stoichiometric, reduced and doped CeO(2). We use a dipole polarizable potential (DIPPIM: the dipole polarizable ion model) and optimize its parameters by fitting them to a series of density functional theory calculations. The resulting potential was tested by calculating a series of fundamental properties for CeO(2) and by comparing them against experimental values. The values for all the calculated properties (thermal and chemical expansion coefficients, lattice parameters, oxygen migration energies, local crystalline structure and elastic constants) are within 10-15% of the experimental ones, an accuracy comparable to that of ab initio calculations. This result suggests the use of this new potential for reliably predicting atomic scale properties of CeO(2) in problems where ab initio calculations are not feasible due to their size limitations. PMID:21654047

  7. 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.

  8. 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.

  9. 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

  10. Loss of magnetization induced by doping in CeO2 films

    NASA Astrophysics Data System (ADS)

    Fernandes, V.; Schio, P.; de Oliveira, A. J. A.; Schreiner, W. H.; Varalda, J.; Mosca, D. H.

    2011-12-01

    This work reports the effect of Mn, Fe, Co, and Cu low doping (˜3 at. %) on the ferromagnetic behavior of oxygen-defective CeO2-δ films electrodeposited on SiO2/Si(001). Our results indicate that the incorporation of a small number of 3d dopants with unoccupied outermost atomic orbitals, presumably magnetically active, strongly perturb the ferromagnetic ground-state associated with the network of electron clouds surrounding oxygen vacancies. As a consequence, a strong loss of magnetization occurs and saturation magnetization becomes uncorrelated with number of oxygen vacancies.

  11. Photoluminescent properties of Eu3+ doped electrospun CeO2 nanofibers

    NASA Astrophysics Data System (ADS)

    Fang, Dong; Zhang, Min; Luo, Zhiping; Cao, Tingting; Wang, Qing; Zhou, Zhi; Jiang, Ming; Xiong, Chuanxi

    2014-12-01

    In this study, CeO2 nanofibers and that doped with Eu3+ were prepared via a facile electrospinning route and annealed at different temperatures ranging from 500 to 900 °C. Their structures were investigated using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Photoluminescence properties of the nanofibers were studied in detail. It was found that the nanofibers with Eu% concentration of 0.67 mol.% and annealed at 700 °C exhibited the highest intensities of the luminescence peaks between 550 and 650 nm.

  12. 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.

  13. Infrared and visible emissions of rare-earth-doped CeO2 phosphor.

    PubMed

    Chandrakar, D; Kaur, J; Dubey, V; Suryanarayana, N S; Parganiha, Y

    2015-12-01

    This paper reports the synthesis and characterization of Er(3+)-doped CeO2 phosphor with variable concentrations of erbium. The sample was synthesized using a solid-state reaction method, which is useful for the large-scale production of phosphors and is also eco-friendly. The prepared sample was characterized using an X-ray diffraction (XRD) technique. The XRD pattern confirmed that sample has the pure cubic fluorite crystal structure of CeO2. The crystallite size of the prepared phosphor was determined by Scherer's formula and the crystallite size giving an intense XRD peak is 40.06 nm. The surface morphology of the phosphor was determined by field emission gun scanning electron microscopy (FEGSEM). From the FEGSEM image, good surface morphology with some agglomerates was found. The functional group in the prepared sample was analysed by Fourier transform infrared (FTIR) spectroscopy. All samples prepared with variable concentrations of Er(3+) (0.1-2 mol%) were studied by photoluminescence analysis and it was found that the excitation spectra of the prepared phosphor shows broad excitation centred at 251 nm. Emission spectra at different concentrations of Er(3+) show strong peaks at 413 and 470 nm and a weaker peak at 594 nm. The dominant peaks at 413 and 470 nm are caused by the allowed electronic transition (4)S3/2 → (4)I15/2 and the weaker transition at 594 nm is due to the transition (4)F9/2 → (4)I15/2. Spectrophotometric determinations of peaks were evaluated using the Commission Internationale de I'Eclairage (CIE) technique. The emission spectra were also observed using an infrared (IR) laser 980 nm source, and three distinct peaks were found in the IR region at 848, 870 and 980 nm. The prepared phosphor has utility for application in display devices. PMID:25810371

  14. Electroluminescence from metal-oxide-semiconductor devices with erbium-doped CeO2 films on silicon

    NASA Astrophysics Data System (ADS)

    Lv, Chunyan; Zhu, Chen; Wang, Canxing; Gao, Yuhan; Ma, Xiangyang; Yang, Deren

    2015-04-01

    We report on erbium (Er)-related electroluminescence (EL) in the visible and near-infrared (NIR) from metal-oxide-semiconductor (MOS) devices with Er-doped CeO2 (CeO2:Er) films on silicon. The onset voltage of such EL under either forward or reverse bias is smaller than 10 V. Moreover, the EL quenching can be avoidable for the CeO2:Er-based MOS devices. Analysis on the current-voltage characteristic of the device indicates that the electron transportation at the EL-enabling voltages under either forward or reverse bias is dominated by trap-assisted tunneling mechanism. Namely, electrons in n+-Si/ITO can tunnel into the conduction band of CeO2 host via defect states at sufficiently high forward/reverse bias voltages. Then, a fraction of such electrons are accelerated by electric field to become hot electrons, which impact-excite the Er3+ ions, thus leading to characteristic emissions. It is believed that this work has laid the foundation for developing viable silicon-based emitters using CeO2:Er films.

  15. 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.

  16. 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

  17. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

    2015-10-01

    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.

  19. 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

  20. 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

  1. 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

  2. Structure and growth morphology of Gd 2O 3-doped CeO 2 thin films

    NASA Astrophysics Data System (ADS)

    Jiang, Xuening; Hao, Binkui

    2010-05-01

    Gd 2O 3-doped CeO 2 (Gd 0.1Ce 0.9O 1.95, GDC) thin films were synthesized on (1 0 0) Si single crystal substrates by a reactive radio frequency magnetron sputtering technique. Structures and surface morphologies were characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and one-dimensional power spectral density (1DPSD) analysis. The XRD patterns indicated that, in the temperature range of 200-700 °C, f.c.c. structured GDC thin films were formed with growth orientations varying with temperature—random growth at 200 °C, (2 2 0) textures at 300-600 °C and (1 1 1) texture at 700 °C. GDC film synthesized at 200 °C had the smoothest surface with roughness of Rrms=0.973 nm. Its 1DPSD plot was characterized with a constant part at the low frequencies and a part at the high frequencies that could be fitted by the f-2.4 power law decay. Such surface feature and scaling behavior were probably caused by the high deposition rate and random growth in the GDC film at this temperature. At higher temperatures (300-700 °C), however, an intermediate frequency slope (- γ2≈-2) appeared in the 1DPSD plots between the low frequency constant part and the high frequency part fitted by f-4 power law decay, which indicated a roughing mechanism dominated by crystallographic orientation growth that caused much rougher surfaces in GDC films ( Rrms>4 nm).

  3. 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. PMID:26030478

  4. The peak effect in bulk Y-Ba-Cu-O superconductor with CeO2 doping by the infiltration growth method

    NASA Astrophysics Data System (ADS)

    Chen, Po-Wei; Chen, In-Gann; Chen, Shih-Yun; Wu, Maw-Kuen

    2011-08-01

    In this study, large single grain Y-Ba-Cu-O (YBCO) superconductors with CeO2 addition were fabricated by the infiltration and growth (IG) technique. It is noticeable that the CeO2 doped IG-YBCO sample showed a superior critical current density Jc(H, T) with a peak effect. The Jc (3 T, 65 K) of the IG-YBCO sample with CeO2 addition reached 105 A cm - 2, which was two times higher than that of the CeO2 doped top-seeded melt texture (TSMT)-YBCO sample. Microstructure analysis indicated that the concentration of Sm in the CeO2 doped IG-YBCO sample was 0.2 mol%. The Sm which dissolved from the SmBCO seed diffused into the bulk to form compositional fluctuations of (Y, Sm)BCO and was correlated to the effective pinning in high field regions (or peak effect) to improve the Jc(H, T) in high fields. In addition, the maximum trapped field value of 0.23 T and trapped field profile of the CeO2 doped sample grown by IG are larger than that of 0.13 T grown by TSMT using the same diameter of precursor pellets.

  5. Ethanol Sensor of CdO/Al2O3/CeO2 Obtained from Ce-DOPED Layered Double Hydroxides with High Response and Selectivity

    NASA Astrophysics Data System (ADS)

    Xu, Dongmei; Guan, Meiyu; Xu, Qinghong; Guo, Ying; Wang, Yao

    2013-06-01

    In this paper, Ce-doped CdAl layered double hydroxide (LDH) was first synthesized and the derivative CdO/Al2O3/CeO2 composite oxide was prepared by calcining Ce-doped CdAl LDH. The structure, morphology and chemical state of the Ce doped CdAl LDH and CdO/Al2O3/CeO2 were also investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), solid state nuclear magnetic resonance (SSNMR), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The gas sensing properties of CdO/Al2O3/CeO2 to ethanol were further studied and compared with CdO/Al2O3 prepared from CdAl LDH, CeO2 powder as well as the calcined Ce salt. It turns out that CdO/Al2O3/CeO2 sensor shows best performance in ethanol response. Besides, CdO/Al2O3/CeO2 possesses short response/recovery time (12/72 s) as well as remarkable selectivity in ethanol sensing, which means composite oxides prepared from LDH are very promising in gas sensing application.

  6. Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

    NASA Astrophysics Data System (ADS)

    Sun, Lixin; Marrocchelli, Dario; Yildiz, Bilge

    2015-02-01

    Strained oxide thin films are of interest for accelerating oxide ion conduction in electrochemical devices. Although the effect of elastic strain has been uncovered theoretically, the effect of dislocations on the diffusion kinetics in such strained oxides is yet unclear. Here we investigate a 1/2<110>{100} edge dislocation by performing atomistic simulations in 4-12% doped CeO2 as a model fast ion conductor. At equilibrium, depending on the size of the dopant, trivalent cations and oxygen vacancies are found to simultaneously enrich or deplete either in the compressive or in the tensile strain fields around the dislocation. The associative interactions among the point defects in the enrichment zone and the lack of oxygen vacancies in the depletion zone slow down oxide ion transport. This finding is contrary to the fast diffusion of atoms along the dislocations in metals and should be considered when assessing the effects of strain on oxide ion conductivity.

  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. PMID:27474851

  8. 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.

  9. 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. PMID:27108893

  10. 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. PMID:26699802

  11. 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.

  12. 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.

  13. 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.

  14. High power density cell using nanostructured Sr-doped SmCoO3 and Sm-doped CeO2 composite powder synthesized by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Shimada, Hiroyuki; Yamaguchi, Toshiaki; Suzuki, Toshio; Sumi, Hirofumi; Hamamoto, Koichi; Fujishiro, Yoshinobu

    2016-01-01

    High power density solid oxide electrochemical cells were developed using nanostructure-controlled composite powder consisting of Sr-doped SmCoO3 (SSC) and Sm-doped CeO2 (SDC) for electrode material. The SSC-SDC nano-composite powder, which was synthesized by spray pyrolysis, had a narrow particle size distribution (D10, D50, and D90 of 0.59, 0.71, and 0.94 μm, respectively), and individual particles were spherical, composing of nano-size SSC and SDC fragments (approximately 10-15 nm). The application of the powder to a cathode for an anode-supported solid oxide fuel cell (SOFC) realized extremely fine cathode microstructure and excellent cell performance. The anode-supported SOFC with the SSC-SDC cathode achieved maximum power density of 3.65, 2.44, 1.43, and 0.76 W cm-2 at 800, 750, 700, and 650 °C, respectively, using humidified H2 as fuel and air as oxidant. This result could be explained by the extended electrochemically active region in the cathode induced by controlling the structure of the starting powder at the nano-order level.

  15. Spectroscopic study of ZnO doped CeO 2-PbO-B 2O 3 glasses

    NASA Astrophysics Data System (ADS)

    Pal Singh, Gurinder; Singh, D. P.

    2011-09-01

    Glass samples of compositions xZnO- xCeO 2-(30- x)PbO-(70- x)B 2O 3 with x varying from 2% to 10% mole fraction are prepared by the melt quench technique. The structural and optical analysis of glasses is carried out by XRD, FTIR, density and UV-visible spectroscopic measurement techniques. The FTIR spectral analysis indicates that with the addition of ZnO contents in glass network, structural units of BO 3 are transformed into BO 4. It has been observed in our previous work that band gap decreases from 2.89 to 2.30 eV for CeO 2-PbO-B 2O 3 glasses with cerium content varying from 0% to 10% [Gurinder Pal Singh, Davinder Paul Singh, Physica B 406(3) (2011) 640-644]. With the incorporation of zinc in CeO 2-PbO-B 2O 3 glasses, the optical band gap energy decreases further from 2.38 to 2.03 eV. This causes more compaction of the borate network, which results in an increase of density (3.39-4.02 g/cm 3). Transmittance shows that ZnO in glass samples acts as a reducing agent thathelps to convert Ce 4+→Ce 3+ ions.

  16. Molecular dynamics simulation of fast particle irradiation to the Gd2O3-doped CeO2

    NASA Astrophysics Data System (ADS)

    Sasajima, Y.; Ajima, N.; Osada, T.; Ishikawa, N.; Iwase, A.

    2013-12-01

    The structural relaxation caused by the high-energy-ion irradiation of CeO2 with Gd2O3 addition was simulated by the molecular dynamics method. The amount of Gd2O3 was changed from 0 to 25 mol% by 5 mol%. As the initial condition, high thermal energy was supplied to the individual atoms within a cylindrical region of nanometer-order radius located in the center of the specimen. The potential proposed by Inaba et al. was utilized to calculate interaction between atoms [H. Inaba, R. Sagawa, H. Hayashi, K. Kawamura, Solid State Ionics 122 (1999) 95-103]. The supplied thermal energy was first spent to change the crystal structure into an amorphous one within a short period of about 0.3 ps, then it dissipated in the specimen. By increasing the concentration of Gd2O3, more structural disorder was observed in the sample, which is consistent to the actual experiment.

  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. 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

  19. A novel spectrofluorometric method for the determination of arsenic in human hair using Dy2O3-doped CeO2 nanoparticles.

    PubMed

    Hosseini, Mohammad Saeid; Belador, Foroogh

    2014-10-01

    This paper describes a simple and inexpensive method for the determination of arsenic in human hair samples based on spectrofluorometric detection. The applied Dy2O3-doped CeO2 (DDC) nanoparticles were synthesized using microwave-induced combustion technique and subjected to analytical samples containing As(V) species. At optimum conditions (pH 6, DDC concentration 3 mg L(-1) and excitation/emission wavelengths 250 nm/352 nm), the fluorescence emission of DDC nanoparticles was diminished by increasing the As(V) concentration present in the medium. The co-existent ions present in hair were not interfered. A method for the speciation of As(III) and As(V) is also described. The method was validated using a well-known separation/spectrofluorometric method. There was no significant difference at the 95% confidence level between the results of the two methods. The proposed method is characterized by a wide analytical concentration range (5.0 × 10(-8)-1.0 × 10(-5) M), a detection limit for As(V) of 1 × 10(-8) mol L(-1) and relative standard deviation of 1.4%. The recoveries for the spiked amounts of As(V) was found to be 93.3-104.0%. PMID:25096195

  20. 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.

  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. 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. PMID:27157753

  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. PMID:27483759

  4. Ionic conductivity in Gd-doped CeO2: Ab initio color-diffusion nonequilibrium molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Nilsson, Johan O.; Vekilova, Olga Yu.; Hellman, Olle; Klarbring, Johan; Simak, Sergei I.; Skorodumova, Natalia V.

    2016-01-01

    A first-principles nonequilibrium molecular dynamics (NEMD) study employing the color-diffusion algorithm has been conducted to obtain the bulk ionic conductivity and the diffusion constant of gadolinium-doped cerium oxide (GDC) in the 850-1150 K temperature range. Being a slow process, ionic diffusion in solids usually requires simulation times that are prohibitively long for ab initio equilibrium molecular dynamics. The use of the color-diffusion algorithm allowed us to substantially speed up the oxygen-ion diffusion. The key parameters of the method, such as field direction and strength as well as color-charge distribution, have been investigated and their optimized values for the considered system have been determined. The calculated ionic conductivity and diffusion constants are in good agreement with available experimental data.

  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. PMID:23901509

  6. Solid-state reaction synthesis and aqueous durability of Ce-doped zirconolite-rich ceramics

    NASA Astrophysics Data System (ADS)

    Wen, Guanjun; Zhang, Kuibao; Yin, Dan; Zhang, Haibin

    2015-11-01

    In this study, Ce-doped zirconolite-rich ceramics were prepared by solid-state reaction process using cerium as the surrogate of tetravalence actinide nuclide. The occupancy of Ce in the waste forms was investigated. The aqueous durability of Ce-doped zirconolite-rich ceramic was examined as well. The results show that zirconolite and pseudobrookite coexisted after being sintered at 1200 °C for 6 h. Meanwhile, perovskite is inevitable generated during the process. CeO2 can be successfully incorporated into the lattice structure of the zirconolite-rich ceramics. The maximum containing capacity of CeO2 is up to 14.95 wt% or y = 0.4. The normalized elemental leaching rates of Ce and Ca are fairly constant in low values of 1.2 × 10-6 and 2.3 × 10-2 g m-2 d-1 after 28 days. The normalized leaching rate of Fe is also in a low value of 2.9 × 10-4 g m-2 d-1 after 7 days.

  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. PMID:25288555

  8. Effects of Ce3+ doping concentrations on microstructure and luminescent properties of Ce3+:Lu3Al5O12 (Ce:LuAG) transparent ceramics

    NASA Astrophysics Data System (ADS)

    Xu, Jian; Fan, Lingcong; Shi, Ying; Li, Junlang; Xie, Jianjun; Lei, Fang

    2014-10-01

    Ce3+ doping behaviour in range from 1.0 to 10.0 mol% on Ce:LuAG polycrystalline powders and ceramics was investigated in this paper. It was found that CeO2 would segregate as secondary phase from Ce:LuAG powders when the Ce3+ doping concentration reached to 5.0 mol% under the calcination of 1100 °C for 10 h in air. However, this “over-doped” phenomenon disappeared after the powders being densified into transparent ceramics by vacuum sintering. When the Ce3+ doping concentration was further increased into 10.0 mol%, the CeO2 segregation regions were observed in the corresponding Ce:LuAG ceramic with an elongated rod morphology. The drastic dropping of in-line optical transmittance of the 10.0 mol% Ce:LuAG ceramic demonstrated that the CeO2 secondary phase would form defects and/or electron traps at grain boundaries which embarrassed the energy transfer from host lattice to Ce3+ luminescent centers leading to its poor scintillation property.

  9. Upconversion studies on Yb3+/Er3+ doped CeO2 and CeF3 phosphors: Enhanced near infrared emission

    NASA Astrophysics Data System (ADS)

    Singh, A. K.; Kumar, K.; Rai, S. B.; Kumar, D.

    2013-09-01

    Upconversion emission in CeF3: Er3+/Yb3+ and CeO2: Er3+/Yb3+ phosphors is studied using 976 nm diode laser excitation and the emission results are compared. The Ce3+ ion is found to interact with Er3+ ion that enhances the energy transfer rate among the levels of Er3+ ion. The increased energy transfer rate enables increase in the infrared emission (˜1530 nm) at the expense of visible upconversion emission. An intense emission at ˜1530 nm due to the 4I13/2→4I15/2 transition of Er3+ ion, with least emission in the UV/visible region, is observed in the CeF3: Er3+/Yb3+ phosphor. The emission intensity of 4I13/2→4I15/2 transition is also compared for LaF3, CeF3 and LaF3 hosts and it is found that the emission intensity is maximum for CeF3 host. The CeF3: Er3+/Yb3+ phosphor is found suitable for optical amplifiers, laser materials and infrared imaging probes around 1530 nm.

  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. Spectroscopic characterization of Co3O4 catalyst doped with CeO2 and PdO for methane catalytic combustion

    NASA Astrophysics Data System (ADS)

    Jodłowski, P. J.; Jędrzejczyk, R. J.; Rogulska, A.; Wach, A.; Kuśtrowski, P.; Sitarz, M.; Łojewski, T.; Kołodziej, A.; Łojewska, J.

    2014-10-01

    The study deals with the XPS, Raman and EDX characterization of a series of structured catalysts composed of cobalt oxides promoted by palladium and cerium oxides. The aim of the work was to relate the information gathered from spectroscopic analyses with the ones from kinetic tests of methane combustion to establish the basic structure-activity relationships for the catalysts studied. The most active catalyst was the cobalt oxide doped with little amount of palladium and wins a confrontation with pure palladium oxide catalyst which is commercially used in converters for methane. The analyses Raman and XPS analyses showed that this catalyst is composed of a cobalt spinel and palladium oxide. The quantitative approach to the composition of the catalysts by XPS and EDX methods revealed that the surface of palladium doped cobalt catalyst is enriched with palladium oxide which provides a great number of active centres for methane combustion indicated by kinetic parameters.

  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. PMID:25637793

  13. 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.

  14. 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.

  15. 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

  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. Optical Ceramics Based on Yttrium Oxide Doped with Tetravalent Ions

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Optical ceramics activated by neodymium or ytterbium and based on Y2O3 with inclusions of CeO2 , ZrO2 , and HfO2 containing optical inhomogeneities in the form of an orange peel are investigated. It is indicated that in the ceramics with such inclusions not only the crystallite size and porosity, but also the transmission near the edge of the fundamental absorption band decrease, and the theoretically predicted transparency is not achieved (even in the infrared range). It is reported that in the ceramics containing Hf 4+ and Zr4+ , Hf 3+ and Zr3+ , additionally depopulating the 4 F 3/2 upper laser level of the Nd3+ ion activator, are also present. The dependences of the Nd:Y2O3 crystal lattice parameter on the Hf 4+ or Nd3+ content in it, constructed based on the results of x-ray diffraction analysis, are linear, that is, no peculiarities are observed for solid solutions of these compounds. Energy dispersion analysis with a resolution of about 1 μm also indicates the uniformity of the distribution of the chemical elements throughout the sample. At the same time, estimates based on the Rayleigh light scattering in the ceramics indicate that one of the additional phases must have sizes smaller than λ/20 = 20 nm. By the method of high-resolution transmission electron microscopy, particles with composition modulated on the nanolevel are detected in the 90(Nd0.01Y0.99)2O3 + 10HfO2 nanopowder from which the ceramics are synthesized given that the lattice period remains unchanged.

  18. Synthesis of Pu-Doped Ceramic

    SciTech Connect

    Anderson, E. B

    1998-09-02

    Plutonium-doped zircon containing about 10 wt% Pu was synthesized in this cooperative project between Russia and the United States conducted at the V. G. Khlopin Radium Institute. The sol-gel method was used for starting precursor preparation to provide complete mixing of initial components and to avoid dust formation inside the glove-box. The sol-gel process also gives interim Pu stabilization in the form of amorphous zirconium hydrosilicate (AZHS), which is a result of gel solidification. AZHS is a solid and relatively durable material that can be easy converted into crystalline zircon by pressureless sintering, thus avoiding significant radioactive contamination of laboratory equipment. A methanol-aqueous solution of tetraethoxysilane Si(OC2H5)4, Pu-nitrate, and zirconil oxynitrate was prepared in final stoichiometry of zircon (Zr,Pu)SiO4 80 wt% + zirconia (Zr,Pu)O2 20 wt%. Gelation occurred after 90 hours at room temperature. AZHS with excess of zirconia 20 wt% was obtained as an interim calcine product and then it was converted into zircon/zirconia ceramic by sintering at 1490 to 1500°C in air for different time periods. The samples obtained were studied by SRD and ESEM methods. It was found that both zircon yield and zircon cell parameters that are correlated with Pu incorporation depend on sintering time.

  19. Thermal analysis on grad-doped active-mirror Yb:YAG ceramic lasers

    NASA Astrophysics Data System (ADS)

    Cheng, Xiaojin; Wang, Jianlei; Jiang, Benxue

    2015-11-01

    Heat conduction, temperature distribution, thermal stress, and thermally induced refractive index of a diode-pumped active-mirror grad-doped Yb:YAG ceramic laser are analyzed and compared to a uniform-doped Yb:YAG ceramic laser. It is found that a rationally designed grad-doped Yb:YAG ceramic has a smaller temperature gradient than a uniform-doped Yb:YAG ceramic with the same absorption pump power, which results in higher output energy in the grad-doped Yb:YAG ceramic laser.

  20. Hydrogenated CeO2-xSx mesoporous hollow spheres for enhanced solar driven water oxidation.

    PubMed

    Xiao, Yuting; Chen, Yajie; Xie, Ying; Tian, Guohui; Guo, Shien; Han, Taoran; Fu, Honggang

    2016-02-11

    A facile route for the fabrication of hydrogenated sulfur-doped CeO2 (H-CeO2-xSx) mesoporous hollow spheres is reported. The spheres exhibited excellent photocatalytic activity due to the synergistic effect of the higher sulfur doping level and hydrogen post-treatment. PMID:26741276

  1. Electrical properties of niobium doped barium bismuth-titanate ceramics

    SciTech Connect

    Bobić, J.D.; Vijatović Petrović, M.M.; Banys, J.; Stojanović, B.D.

    2012-08-15

    Highlights: ► Pure and doped BaBi{sub 4}Ti{sub 4}O{sub 15} were prepared via the solid-state reaction method. ► The grain size was suppressed in Nb-doped samples. ► The diffuseness of the dielectric peak increased with dopant concentration. ► Niobium affected on relaxor behavior of barium bismuth titanate ceramics. ► The conductivity change was noticed in doped samples. -- Abstract: BaBi{sub 4}Ti{sub 4–5/4x}Nb{sub x}O{sub 15} (BBNTx, x = 0, 0.05, 0.15, 0.30) ceramics have been prepared by solid state method. XRD data indicate the formation of single-phase-layered perovskites for all compositions. SEM micrographs suggest that the grain size decreases with Nb doping. The effect of niobium doping on the dielectric and relaxor behavior of BaBi{sub 4}Ti{sub 4}O{sub 15} ceramics was investigated in a wide range of temperatures (20–777 °C) and frequencies (1.21 kHz to 1 MHz). Nb doping influences T{sub c} decrease as well as the decrease of dielectric permittivity at Curie temperature. At room temperature, undoped BaBi{sub 4}Ti{sub 4}O{sub 15} exhibits dielectric constant of ∼204 at 100 kHz, that slightly increases with Nb doping. The conductivity of BBNT5 ceramics is found to be lower than that of other investigated compositions. The value of activation energy of σ{sub DC} was found to be 0.89 eV, 1.01 eV, 0.93 eV and 0.71 eV for BBT, BBNT5, BBNT15 and BBNT30, respectively.

  2. 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.

  3. 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.

  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. PMID:24996153

  5. Thermo-optic quality assessment of doped optical ceramics

    NASA Astrophysics Data System (ADS)

    Willis, Christina C. C.; Bradford, Joshua D.; Maddox, Emily; Shah, Lawrence; Richardson, Martin

    2013-03-01

    The use of optical quality ceramics for laser applications is expanding, and with this expansion there is an increasing need for diagnostics to assess the quality of these materials. Ceramic material with flaws and contaminants yields significantly less efficient performance as laser gain media and can generate excessive amounts of waste heat. This is a concern that is especially relevant in high power laser applications where thermally induced damage can be catastrophic. In order to assess a set of ceramic and crystalline samples we induce and measure thermal lensing in order to produce a relative ranking based on the extent of the induced thermal lens. In these experiments thermal lensing is induced in a set of nine 10% Yb:YAG ceramic and single-crystal samples using a high power 940 nm diode, and their thermal response is measured using a Shack-Hartmann wavefront sensor. The materials are also ranked by their transmission in the visible region. Discrepancies between the two ranking methods reveal that transmission in the visible region alone is not adequate for an assessment of the overall quality of ceramic samples. The thermal lensing diagnostic technique proves to be a reliable and quick over-all assessment method of doped ceramic materials without requiring any a priori knowledge of material properties.

  6. 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.

  7. Sintering and mechanical properties of gadolinium-doped ceria ceramics

    NASA Astrophysics Data System (ADS)

    Yasuda, K.; Uemura, K.; Shiota, T.

    2012-01-01

    Gadolinium-doped ceria (GDC) ceramics were made by sintering at various temperatures from 1000°C to 1400°C in air. The true density and apparent density were measured to calculate the relative density of GDC ceramics. The change in relative density revealed that densification of GDC ceramics increased up to 1200°C, and thereafter turned downward. It was suggested that pores were formed at 1300°C and 1400°C due to non-stoichiometry of ceria. JIS-type specimens were cut from the sintered body and tested by 4-point bending. Young's modulus and bending strength decreased with increasing the sintering temperature from 1200°C to 1400°C, corresponding to the change in the relative density.

  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. 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

  10. 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.

  11. Ferromagnetism induced by oxygen and cerium vacancies above the percolation limit in CeO2

    NASA Astrophysics Data System (ADS)

    Fernandes, V.; Schio, P.; de Oliveira, A. J. A.; Ortiz, W. A.; Fichtner, P.; Amaral, L.; Graff, I. L.; Varalda, J.; Mattoso, N.; Schreiner, W. H.; Mosca, D. H.

    2010-06-01

    We studied the structural, chemical and magnetic properties of non-doped ceria (CeO2) thin films electrodeposited on silicon substrates. Experimental results confirm that the observed room temperature ferromagnetism is driven by both cerium and oxygen vacancies. We investigated ceria films presenting vacancy concentrations well above the percolation limit. Irradiation experiments with neon ions were employed to generate highly oxygen defective CeO2 - δ structures. X-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectroscopy were used to estimate the concentration of Ce3 + sites in the films, which can reach up to 50% of Ce3 + replacing Ce4 + , compared to a stoichiometric CeO2 structure. Despite the increment of structural disorder, we observe that the saturation magnetization continuously increases with Ce3 + concentration. Our experiments demonstrate that the ferromagnetism observed in ceria thin films, highly disordered and oxygen-deficient, preserving the fluorite-type structure only in a nanometer scale, remains intrinsically stable at room temperature.

  12. Thermo-optical properties of terbium-aluminum garnet ceramics doped with silicon and titanium.

    PubMed

    Starobor, Aleksey; Palashov, Oleg; Zhou, Shengming

    2016-04-01

    The Verdet constant and thermo-optical characteristics of a Si-doped and Ti-doped terbium aluminum garnet ceramics have been investigated. It is shown that the Verdet constant of the samples is ∼40% higher than that of TGG ceramics at 1064 nm. The best samples of Si:TAG have magneto-optical figures of merit more than 1.5 times greater than those of TGG ceramics. Si:TAG is better than TGG ceramics as a medium for high-power Faraday isolators. PMID:27192274

  13. Preparation and characterization of Yb-doped YAG ceramics

    NASA Astrophysics Data System (ADS)

    Hostaša, Jan; Esposito, Laura; Alderighi, Daniele; Pirri, Angela

    2013-02-01

    This work presents the results of the preparation of polycrystalline Yb:YAG ceramics for laser sources with dopant concentration from 0 up to 20 at.% via solid state reactive sintering. Samples were prepared via cold isostatic pressing of spray dried mixture of pure oxide powders with TEOS as a sintering aid. Sintering was conducted under high vacuum and clean atmosphere. Various sintering cycles were tested, so that optimum conditions could be selected in dependence on Yb concentration. Samples with optical transmittance higher than 80% were prepared and their laser performance was examined. Slope efficiency as high as 73% and a maximum output power of 6 W were obtained for the sample doped with 10% Yb. Final microstructure of prepared samples was analyzed via optical microscopy, scanning and transmission electron microscopy, and EDS.

  14. 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.

  15. Local environment of Fe dopants in nanoscale Fe : CeO2-x oxygen storage material

    NASA Astrophysics Data System (ADS)

    Meledina, M.; Turner, S.; Galvita, V. V.; Poelman, H.; Marin, G. B.; van Tendeloo, G.

    2015-02-01

    Nanoscale Fe : CeO2-x oxygen storage material for the process of chemical looping has been investigated by advanced transmission electron microscopy and electron energy-loss spectroscopy before and after a model looping procedure, consisting of redox cycles at heightened temperature. Separately, the activity of the nanomaterial has been tested in a toluene total oxidation reaction. The results show that the material consists of ceria nanoparticles, doped with single Fe atoms and small FeOx clusters. The iron ion is partially present as Fe3+ in a solid solution within the ceria lattice. Furthermore, enrichment of reduced Fe2+ species is observed in nanovoids present in the ceria nanoparticles, as well as at the ceria surface. After chemical looping, agglomeration occurs and reduced nanoclusters appear at ceria grain boundaries formed by sintering. These clusters originate from surface Fe2+ aggregation, and from bulk Fe3+, which ``leaks out'' in reduced state after cycling to a slightly more agglomerated form. The activity of Fe : CeO2 during the toluene total oxidation part of the chemical looping cycle is ensured by the dopant Fe in the Fe1-xCexO2 solid solution, and by surface Fe species. These measurements on a model Fe : CeO2-x oxygen storage material give a unique insight into the behavior of dopants within a nanosized ceria host, and allow to interpret a plethora of (doped) cerium oxide-based reactions.Nanoscale Fe : CeO2-x oxygen storage material for the process of chemical looping has been investigated by advanced transmission electron microscopy and electron energy-loss spectroscopy before and after a model looping procedure, consisting of redox cycles at heightened temperature. Separately, the activity of the nanomaterial has been tested in a toluene total oxidation reaction. The results show that the material consists of ceria nanoparticles, doped with single Fe atoms and small FeOx clusters. The iron ion is partially present as Fe3+ in a solid solution

  16. Electrical and reliability characteristics of Mn-doped nano BaTiO3-based ceramics for ultrathin multilayer ceramic capacitor application

    NASA Astrophysics Data System (ADS)

    Gong, Huiling; Wang, Xiaohui; Zhang, Shaopeng; Tian, Zhibin; Li, Longtu

    2012-12-01

    Nano BaTiO3-based dielectric ceramics were prepared by chemical coating approach, which are promising for ultrathin multilayer ceramic capacitor (MLCC) applications. The doping effects of Mn element on the microstructures and dielectric properties of the ceramics were investigated. The degradation test and impedance spectroscopy were employed to study the resistance degradation and the conduction mechanism of Mn-doped nano-BaTiO3 ceramic samples. It has been found that the reliability characteristics greatly depended on the Mn-doped content. Moreover, the BaTiO3 ceramic with grain size in nanoscale is more sensitive to the Mn-doped content than that in sub-micron scale. The addition of 0.3 mol. % Mn is beneficial for improving the reliability of the nano BaTiO3-based ceramics, which is an important parameter for MLCC applications. However, further increasing the addition amount will deteriorate the performance of the ceramic samples.

  17. 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

  18. 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.

  19. Water Adsorption and Dissociation on CeO2 (111)

    NASA Astrophysics Data System (ADS)

    Gao, Yi; Han, Zhong-Kang; Shao, Nan; Mei, Wai-Ning

    The complexity and flexibility of ceria surface hinders the fully understanding of its reactivity and real applications. Here, we use H2O/CeO2(111) as the model system to investigate the water effect on the electron localization and vacancy diffusion on CeO2(111) surface by the first-principle calculations. Our results indicate the water adsorption would high affect the electronic structures of CeO2(111) surface, which further induce the dissociation of H2O molecule. This molecular mechanism might provide more guidance to the future applications including the watergas shift reactions.

  20. 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.

  1. 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

  2. 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.

  3. Differential scanning calorimetry investigations on Eu-doped fluorozirconate-based glass ceramics

    PubMed Central

    Paßlick, C.; Ahrens, B.; Henke, B.; Johnson, J. A.; Schweizer, S.

    2010-01-01

    The properties of Eu-doped fluorochlorozirconate (FCZ) glass ceramics upon thermal processing and the influence of Eu-doping on the formation of BaCl2 nanocrystals therein have been investigated. Differential scanning calorimetry indicates that higher Eu-doping shifts the crystallization peak of the nanocrystals in the glass to lower temperatures, while the glass transition temperature remains constant. The activation energy and the thermal stability parameters for the BaCl2 crystallization are determined. PMID:21286235

  4. 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)

  5. Electrical properties of palladium-doped CaCu3Ti4O12 ceramics

    NASA Astrophysics Data System (ADS)

    Singh, Arashdeep; Md Mursalin, Sk.; Rana, P.; Sen, Shrabanee

    2015-09-01

    The effect of doping palladium (Pd) at the Cu site of CaCu3Ti4O12 powders (CCPTO) synthesized by sol-gel technique on electrical properties was studied. XRD analysis revealed the formation of CCTO and CCPTO ceramics with some minor quantities of impurities. SEM micrographs revealed that the grain size decreased with Pd doping. TEM micrographs of CCPTO powder showed the formation of irregular-shaped particles of ~40 nm. The dielectric constant and dielectric loss showed a significant enhancement with Pd doping. A significant decrease in grain-boundary resistance with Pd doping was ascertained by impedance spectroscopy study.

  6. 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

  7. Ceramics

    NASA Astrophysics Data System (ADS)

    Yao, Lichun; Yang, Jian; Qiu, Tai

    2014-09-01

    The effects of CuO addition on phase composition, microstructure, sintering behavior, and microwave dielectric properties of 0.80Sm(Mg0.5Ti0.5)O3-0.20 Ca0.8Sr0.2TiO3(8SMT-2CST) ceramics prepared by a conventional solid-state ceramic route have been studied. CuO addition shows no obvious influence on the phase of the 8SMT-2CST ceramics and all the samples exhibit pure perovskite structure. Appropriate CuO addition can effectively promote sintering and grain growth, and consequently improve the dielectric properties of the ceramics. The sintering temperature of the ceramics decreases by 50°C by adding 1.00 wt.%CuO. Superior microwave dielectric properties with a ɛ r of 29.8, Q × f of 85,500 GHz, and τ f of 2.4 ppm/°C are obtained for 1.00 wt.%CuO doped 8SMT-2CST ceramics sintered at 1500°C, which shows dense and uniform microstructure as well as well-developed grain growth.

  8. 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

    2016-07-01

    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%.

  9. 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.

  10. 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.

  11. Enhanced Multiferroic Properties of BiFeO3 Ceramics by mo Doping

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Zhang, G. Q.; Miao, J.; Xu, X. G.; Jiang, Y.

    We have investigated the magnetic and electrical properties of multiferroic BiFe1-xMoxO3 ceramics (BFMO, x = 0.0%, 0.2%, 0.5% and 0.8%) prepared by the sol-gel method. The phase structure of BFMO samples were confirmed by X-ray diffraction. It was found that the substitution of Mo is responsible for the increasing of the magnetization in BFMO ceramics. Moreover, both dielectric and polarization-electric field properties suggest that the Mo doping could improve the dielectric and ferroelectric properties in BFMO ceramic.

  12. Optical properties of Dy3+ doped bismuth zinc borate glass and glass ceramics

    NASA Astrophysics Data System (ADS)

    Shanmugavelu, B.; Kanth Kumar, V. V. Ravi

    2012-06-01

    Dy3+ doped bismuth zinc borate transparent glasses were prepared by melt quenching technique and these glasses were used precursor to obtain transparent glass ceramics by heat treatment method. XRD pattern of the glass ceramic shows the formation of the β-BiB3O6 and Bi2ZnOB2O6 phases. The visible emission intensity of the glass ceramics is stronger than the glass. This can be due to the formation of nano nonlinear optical crystallites in glass matrix.

  13. 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.

  14. 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.

  15. Defect properties of cobalt-doped hexagonal barium titanate ceramics

    NASA Astrophysics Data System (ADS)

    Langhammer, H. T.; Böttcher, R.; Müller, T.; Walther, T.; Ebbinghaus, S. G.

    2015-07-01

    X-ray diffraction (XRD) patterns, electron paramagnetic resonance (EPR) powder spectra (9 and 34 GHz) and the magnetic susceptibility of BaTiO3 + 0.04 BaO + x/2 Co2O3 (0.001 ⩽ x ⩽ 0.02) ceramics were studied to investigate the incorporation of Co ions in the BaTiO3 lattice and their valence states as well as the development of the hexagonal phase (6H modification) in dependence on doping level x and sintering temperature Ts. At Ts = 1400 °C the 6H modification begins to occur at a nominal Co concentration x of about 0.001 and for x > 0.005 the samples are completely hexagonal at room temperature. Two different EPR spectra were observed in the 6H modification of BaTiO3, which were both assigned to paramagnetic Co2+ ions located at the two crystallographically non-equivalent Ti sites in 6H-BaTiO3. The EPR g tensor values as well as the molar paramagnetic susceptibility, measured in the temperature range 5 K-300 K at a magnetic field of 9 T, were analyzed in the framework of the ligand field theory using the program CONCORD. The combination of EPR and magnetic measurements reveals that in air-sintered 6H BaTiO3, the incorporated Co occurs as a mixture of paramagnetic Co2+ and diamagnetic Co3+ ions, whereas in samples annealed in reducing atmosphere the majority of Co is in the divalent state. The occurrence of Co4+ can be excluded for all investigated samples. The sample color caused by Co2+ and Co3+ ions is beige/light yellow and dark grey/black, respectively. The majority of the Co2+ ions substitutes Ti in the exclusively corner-sharing oxygen octahedra possessing nearly cubic symmetry. The corresponding ligand field parameter B04(3) amounts to about -28 000 cm-1 (Wybourne notation, 10Dq ≈ 20 000 cm-1). In the reduced samples nearly 5% of the detected Co2+ ions occupy the Ti site in the face-sharing oxygen octahedra, which are significantly trigonally distorted. The negative sign of the obtained ligand field parameter B02 ≈ -7300 cm-1

  16. 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. PMID:19079513

  17. EPR on Y-ceramics and Bi-vitroceramics doped with S state paramagnetic ions

    NASA Astrophysics Data System (ADS)

    Simon, Simion; Ilonca, Gheorghe; Barbur, Ioan; Ardelean, Ioan; Redac, Radu

    1989-12-01

    The effect of Gd doping and of thermal history on the EPR spectra from Y 1-xGd xBa 2Cu 3O 7-δ ceramics and, for the first time, from Bi 2-xGd xSr 2Ca 2O z vitroceramics was investigated. The results were correlated with the superconducting properties of the studied samples.

  18. Laser ceramic materials for subpicosecond solid-state lasers using Nd3+-doped mixed scandium garnets.

    PubMed

    Okada, Hajime; Tanaka, Momoko; Kiriyama, Hiromitsu; Nakai, Yoshiki; Ochi, Yoshihiro; Sugiyama, Akira; Daido, Hiroyuki; Kimura, Toyoaki; Yanagitani, Takagimi; Yagi, Hideki; Meichin, Noriyuki

    2010-09-15

    We have successfully developed and demonstrated broadband emission Nd-doped mixed scandium garnets based on laser ceramic technology. The inhomogeneous broadening of Nd(3+) fluorescence lines results in a bandwidth above 5 nm that is significantly broader than that for Nd:YAG and enables subpicosecond mode-locked pulse durations. We have also found the emission cross section of 7.8 × 10(-20) cm(2) to be adequate for efficient energy extraction and thermal conductivity of 4.7 W/mK from these new Nd-doped laser ceramics. The new laser ceramics are good candidates for laser host material in a diode-pumped subpicosecond laser system with high efficiency and high repetition rate. PMID:20847774

  19. Structure and distortion of lead fluoride nanocrystals in rare earth doped oxyfluoride glass ceramics.

    PubMed

    Ge, Jin; Zhao, Lijuan; Guo, Hui; Lan, Zijian; Chang, Lifen; Li, Yiming; Yu, Hua

    2013-10-28

    A series of rare earth (RE) doped oxyfluoride glasses with the composition of (45-x) SiO2-5Al2O3-40PbF2-10CdF2-xRe2O3 (x = 1, 5, 10, 15) (mol%) were prepared by a traditional melt-quenching method. Glass ceramics (GCs) were obtained after thermal treatment and characterized by X-ray diffraction (XRD) to investigate the nanocrystal structure and distortion. Both the dopant type and the doping level play an important role in the distortion of the PbF2-RE lattice. It is found that a cubic Pb3REF9 phase forms in low doping GCs, a tetragonal PbREF5 phase forms in middle doping GCs and cubic PbRE3F11 forms in high doping GCs. Accordingly, the site symmetry of RE(3+) dopants in β-PbF2 nanocrystal undergoes a transition of Oh···D4h···Oh with the increase of doping level. The change in the ligands coordinating the RE(3+) ions was further illustrated by the optical changes in Yb-doped GCs. This paper provides insights on the nanocrystal structure of RE at the atomic level and tries to make a complete description of the nanocrystal structure and distortion in these glass-ceramic materials, which will benefit the optimization of optical properties. PMID:24019159

  20. 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.

  1. Preparation and photocatalytic property of CeO 2 lamellar

    NASA Astrophysics Data System (ADS)

    Chen, Fengjuan; Cao, Yali; Jia, Dianzeng

    2011-08-01

    A novel room temperature solid-state chemical synthesis was introduced to successfully fabricate CeO 2 samples, coupled by a polyethylene glycol 400 (PEG 400)/cetyl trimethylammonium bromide (CTAB)/sodium dodecyl sulfate (SDS). The as-prepared products were characterized by XRD, TEM, SEM, BET and UV. A study of photocatalytic degradation of the methylene blue MB under UV illumination has been carried out. It is indicated that the samples exhibit excellent photocatalytic activity. Besides, the samples assisted with surfactants possess higher photocatalytic activity than the sample without any surfactants, wherein the sample with SDS as an additive shows the highest photocatalytic activity, which is able to reach 89.6% MB degradation ratio within 60 min illumination. Moreover, the effects of important operational parameters such as initial MB concentration, catalyst loading and pH were also investigated. The above sample under the optimum conditions obtained the maximum MB degradation ratio up to 96.5%, which is higher than that of the commercial TiO 2 P25 under the same conditions. It can be concluded that CeO 2 will be a potential photocatalyst in the application of organic pollutant.

  2. Oxygen Diffusion in Nanocrystalline CeO2

    SciTech Connect

    Saraf, Laxmikant V.; Shutthanandan, V; Wang, Chong M.; Zhang, Yanwen; Marina, Olga A.; Thevuthasan, Suntharampillai

    2003-08-14

    A unique ability of CeO2 to gain or lose oxygen ion has valued importance in the area of solid oxide fuel cells and catalysts. The macroscopic nature of oxygen storage, release and thereby vacancy generation, transport is explained with the help of quantum mechanical phenomena of electron localization. In this study, 18O diffusion and related transport on 1-2 mm thick nanocrystalline ceria films prepared by sol-gel process with an average grain-size in the range of 3-6 nm are studied. Initial 18O diffusion results indicate increased diffusion in 6 nm average grain-size nano-ceria films compared to {approx} 38 nm average grain-size poly-ceria films. Conductivity values in the case of {approx} 3nm average grain size CeO2 films grown at 300 0C observed to be marginally increased compared to {approx} 6 nm average grain size ceria films grown at 450 0C. A detailed nano-grain analysis by high-resolution transmission electron microscopy (HRTEM) was carried out to understand the effect of nanocrystallinity on the blocking phenomena.

  3. Visible light induced degradation of methylene blue using CeO2/V2O5 and CeO2/CuO catalysts.

    PubMed

    Saravanan, R; Joicy, S; Gupta, V K; Narayanan, V; Stephen, A

    2013-12-01

    In the present study, the nanocatalysts CeO2, V2O5, CuO, CeO2/V2O5 and CeO2/CuO were synthesized by thermal decomposition method. This method is simple, fast and cost effective compared with other preparation methods. The synthesized catalysts were characterized by different techniques. The XRD and XPS results confirmed the structure and the oxidization states of the nanocomposite materials. DRS results suggested that the prepared CeO2/V2O5 and CeO2/CuO nanocomposites can generate more electrons and holes under visible light irradiation. The photocatalytic activities of prepared catalysts were evaluated using the degradation of aqueous methylene blue solution as a model compound under visible light irradiation. In addition, the nanocomposite (CeO2/V2O5 and CeO2/CuO) materials were employed to degrade the textile effluent under visible light condition. PMID:24094180

  4. Processing and scintillation properties of Eu 3+ doped Lu 2O 3 transparent ceramics

    NASA Astrophysics Data System (ADS)

    Shi, Y.; Chen, Q. W.; Shi, J. L.

    2009-03-01

    A novel processing was developed to fabricate transparent europium (Eu 3+) ion doped lutetia (Lu 2O 3) scintillation ceramics. The microstructural evolution of Eu 3+:Lu 2O 3 phosphor powder under different calcining temperatures was investigated by FTIR and TEM. Highly transparent polycrystalline Lu 2O 3 ceramics were densified from as-prepared powder by pressureless sintering under 1850 °C for 6 h in flowing H 2 atmosphere. Optical linear transmittances in the visible wavelength region for Lu 2O 3 ceramic could reach as high as above 80%. Integration of the X-ray excited emission spectra showed that Lu 2O 3:5at%Eu 3+ ceramic scintillator provided about 10 times overall emission intensity with respect to BGO single crystal at room temperature.

  5. 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%).

  6. Investigation of the additive induced doping effects in gelcast soft lead zirconate titanate ceramics

    SciTech Connect

    Guo Dong; Cai Kai; Li Longtu; Gui Zhilun

    2009-09-01

    Due to the high sensitivity of the electrical properties of electronic ceramics to various factors, knowledge about the possible influence of the processing procedure on their electrical performance is critical for applying a new technique to the fabrication of the materials. In this study, various electrical parameters, complex impedance spectra, ferroelectric hysteresis loops, and microstructures of soft lead zirconate titanate (PZT) ceramics formed by the gelcasting technique from suspensions with various dispersants were investigated in comparison with those of the conventional dry pressed ones. We found that the sodium ion, which is the main cation in many commercial surfactants, exhibited obvious hard doping effects; thus causing deteriorated performance of the gelcast PZT ceramics. While a certain impurity ion introduced by a dispersant was also found to induce soft doping characteristics and improve the electrical performance of the materials. The results suggest that the doping effects of the metal ions or impurities introduced by the dispersants, or other additives, should be generally considered for applying a wet processing technique to forming multicomponent electronic ceramics.

  7. 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.

  8. Phase Formation in PZT Phosphorus-Doped Ceramics

    SciTech Connect

    Celi, L. A.; Caballero, A. C.; Villegas, M.; Moure, C.; Fernandez, J. F.; Eiras, J. A.

    2009-04-19

    The surface modification of lead zirconate titanate (PZT) ceramics with phosphate ester leaves a phosphorus residue absorbed onto the particle surface. During the sintering processes, this surface layer reacts with the PZT to form lead-rich compounds, such as Pb{sub 3}(PO{sub 4}){sub 2} and Pb{sub 4}(P{sub 2}O{sub 9}). The formation of such a compounds may be the responsible for the grain growth inhibition observed in PZT-modified ceramics, as well as the lead loss reduction.

  9. Ceramics

    NASA Astrophysics Data System (ADS)

    Bin, Tang; Feng, Si; Ying-xiang, Li; He-tuo, Chen; Xiao, Zhang; Shu-ren, Zhang

    2014-11-01

    The effects of Ta2O5/Y2O3 codoping on the microstructure and microwave dielectric properties of Ba(Co0.56Zn0.40)1/3Nb2/3O3- xA- xB (A = 0.045 wt.% Ta2O5; B = 0.113 wt.% Y2O3) ceramics ( x = 0, 1, 2, 4, 8, 16, 32) prepared according to the conventional solid-state reaction technique were investigated. The x-ray diffraction (XRD) results showed that the main crystal phase in the sintered ceramics was BaZn0.33Nb0.67O3-Ba3CoNb2O9. The additional surface phase of Ba8CoNb6O24 and trace amounts of Ba5Nb4O15 second phase were present when Ta2O5/Y2O3 was added to the ceramics. The 1:2 B-site cation ordering was affected by the substitution of Ta5+ and Y3+ in the crystal lattice, especially for x = 4. Scanning electron microscopy (SEM) images of the optimally doped ceramics sintered at 1340°C for 20 h showed a compact microstructure with crystal grains in dense contact. Though the dielectric constant increased with the x value, appropriate addition would result in a tremendous modification of the Q × f and τ f values. Excellent microwave dielectric properties ( ɛ r = 35.4, Q × f = 62,993 GHz, and τ f = 2.6 ppm/°C) were obtained for the ceramic with x = 0.4 sintered in air at 1340°C for 20 h.

  10. 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.

  11. Basic study of Eu2+-doped garnet ceramic scintillator produced by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Sugiyama, Makoto; Yanagida, Takayuki; Fujimoto, Yutaka; Yokota, Yuui; Ito, Akihiko; Nikl, Martin; Goto, Takashi; Yoshikawa, Akira

    2012-12-01

    We report a new discovery of Eu2+-doped bulk garnet ceramic scintillators based on reduction of Eu3+ ions without additives. Eu2+-doped Y3Al5O12 and Lu3Al5O12 ceramics were prepared by spark plasma sintering (SPS) method. Using SPS, the green and blue luminescence was observed under UV lamp excitation for Eu2+-doped Y3Al5O12 and Lu3Al5O12 ceramics, respectively. Under excitation by 241Am alpha-ray the Eu2+ 5d-4f emission was observed in radioluminescence spectra both samples. For the first time, scintillation response due to Eu2+ 5d-4f luminescence was observed in the bulk garnet oxide materials. In addition, Eu-doped Al2O3 prepared by SPS showed Eu2+ 5d-4f emission in the radioluminescence spectrum. It is confirmed that Al is a key element to reduce Eu3+ as well as highly reductive condition in SPS.

  12. Lead fluorosilicate glass ceramics doped with Nd3+, Er3+, and Yb3+

    NASA Astrophysics Data System (ADS)

    Petrova, O. B.; Khomyakov, A. V.

    2013-06-01

    Glasses in the PbF2-PbO-SiO2 system doped with 1 mol % of rare-earth elements (Nd3+, Er3+, or Yb3+) are synthesized and studied. The glasses were heat-treated in order to obtain glass ceramics with a fluoride crystalline phase. The changes in the structure and spectral optical properties of glass ceramics with respect to initial glasses were determined by using X-ray diffraction analysis and by studying the luminescent characteristics of dopant ions.

  13. Optical absorption and luminescence study of cobalt-doped magnesium aluminosilicate glass ceramics

    NASA Astrophysics Data System (ADS)

    Malyarevich, A. M.; Denisov, I. A.; Yumashev, K. V.; Dymshits, O. S.; Zhilin, A. A.

    2002-08-01

    Linear and nonlinear optical properties of cobalt-doped magnesium aluminosilicate transparent glass ceramics that were prepared under different conditions have been studied. It has been shown that absorption and luminescence spectra and absorption bleaching of these glass ceramics are defined mainly by tetrahedrally coordinated Co 2+ ions located in magnesium aluminum spinel nanocrystals. The lifetimes of the 4 T 1 ( 4 F) and 4 T 2 ( 4 F) excited states of the tetrahedral Co 2+ ions were found to be in the ranges 2540 and 120450 ns, respectively, depending on the Co concentration. 2002 Optical Society of America

  14. 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.

  15. Enhanced broadband near-infrared luminescence from Ni in Bi/Ni-doped transparent glass ceramics

    NASA Astrophysics Data System (ADS)

    Wu, Botao; Ruan, Jian; Qiu, Jianrong; Zeng, Heping

    2009-07-01

    Spectral properties of Bi/Ni-doped transparent MgO-Al2O3-Ga2O3-SiO2-TiO2 glass ceramics (GCs) containing spinel solution nanocrystals were investigated. The emission intensity of Ni in Bi/Ni-doped GCs was about 4 times stronger than that of Ni-doped GCs due to energy transfer from Bi to Ni. The Bi/Ni-doped GCs with 0.75 mol% Bi2O3 concentration exhibited a near-infrared emission with full width at half maximum of about 270 nm and a fluorescent lifetime of about 350 µs, making them very promising for applications in broadband optical amplifiers and tunable lasers.

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

    PubMed Central

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

    2011-01-01

    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 (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. PMID:22275772

  17. 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.

  18. 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.

  19. Dielectric Properties of Rare-Earth-Oxide-Doped BaTiO3 Ceramics Fired in Reducing Atmosphere

    NASA Astrophysics Data System (ADS)

    Okino, Yoshikazu; Shizuno, Hisamitsu; Kusumi, Shinya; Kishi, Hiroshi

    1994-09-01

    In order to gain an understanding of highly reliable electrical characteristics for the Ho-doped multilayer ceramic capacitors with Ni electrodes, dielectric properties of various rare-earth-oxide-doped BaTiO3 ceramics were studied. The smaller ionic radius rare-earth-oxide (Dy, Ho, Er)-doped samples showed lower resistivity in reducing atmosphere, but higher resistivity in oxidizing atmosphere at the cooling stage, compared with the larger-ion (La, Sm, Gd)-doped samples. Multilayer ceramic capacitors with Ni electrodes using the smaller-ion-doped materials showed smaller aging rate and longer lifetime. We developed Ni-electrode MLCs with X7R specification as 1 µ F in the 2125 type.

  20. 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.

  1. Microstructure, toughness and flexural strength of self-reinforced silicon nitride ceramics doped with yttrium oxide and ytterbium oxide.

    PubMed

    Zheng, Y. S.; Knowles, K. M.; Vieira, J. M.; Lopes, A. B.; Oliveira, F. J.

    2001-02-01

    Self-reinforced silicon nitride ceramics with additions of either yttrium oxide or ytterbium oxide have been investigated at room temperature after various processing heat treatments. Devitrification of the intergranular phase in these materials is very sensitive to the heat treatment used during processing and does not necessarily improve their strength and toughness. Hot-pressed ceramics without a subsequent devitrification heat treatment were the strongest. The ytterbium oxide-doped silicon nitride ceramics were consistently tougher, but less strong, than the yttrium oxide-doped silicon nitride ceramics. In all the ceramics examined, the fracture toughness showed evidence for R-curve behaviour. This was most significant in pressureless sintered ytterbium oxide-doped silicon nitride ceramics. A number of toughening mechanisms, including crack deflection, bridging, and fibre-like grain pull-out, were observed during microstructural analysis of the ceramics. In common with other silicon nitride-based ceramics, thin amorphous films were found at the grain boundaries in each of the ceramics examined. Arrays of dislocations left in the elongated silicon nitride grains after processing were found to belong to the {101;0}<0001> primary slip system. PMID:11207926

  2. Optical, scintillation and dosimeter properties of MgO translucent ceramic doped with Cr3+

    NASA Astrophysics Data System (ADS)

    Kato, Takumi; Okada, Go; Yanagida, Takayuki

    2016-04-01

    We have investigated the photoluminescence (PL), scintillation and thermally-stimulated luminescence (TSL) dosimeter properties of MgO translucent ceramic doped with Cr3+ ion (0.001, 0.01 and 0.1%). The ceramic samples were synthesized by a Spark Plasma Sintering (SPS) technique. The broad and sharp emission peaks appeared around 600-850 nm in all the samples. The PL decay time constants of all the samples were a few ms which were on the typical order of Cr3+ doped phosphors. As with the PL, the peak resulted from Cr3+ ion was detected in the scintillation spectra. The TSL glow curves showed the main peak around 140 °C. The TSL response was confirmed to be linear to the irradiation dose over the dose range from 0.1 to 1000 mGy.

  3. Preparation and photocatalytic activity of CeO 2/TiO 2 interface composite film

    NASA Astrophysics Data System (ADS)

    Jiang, Bangtong; Zhang, Shengyi; Guo, Xiaozhu; Jin, Baokang; Tian, Yupeng

    2009-03-01

    The CeO 2/TiO 2 and TiO 2/CeO 2 interface composite films were prepared on glass substrates by the sol-gel process via dip-coating and calcining technique. The scanning electron microscopy (SEM) revealed that the TiO 2 layer has a compact and uniformity glasslike surface with 200 nm in thickness, and the CeO 2 layer has a coarse surface with 240 nm in thickness. The X-ray diffractometer (XRD) analysis showed that the TiO 2 layer is made up of anatase phase, and the CeO 2 layer is structured by cubic fluorite phase. Through a series of photo-degradation experiments, the relationship of the photocatalytic activity with the constituents of the films was studied. In virtue of the efficient interfacial charge separation via the process of electron transfer from TiO 2 to CeO 2, the photocatalytic activity of the CeO 2/TiO 2 composite film is high. Contrarily, the photocatalytic activity of the TiO 2/CeO 2 composite film is low, due to its inert surface made up of CeO 2 with broad bandwidth. Apart from the effect of the film structure, the effect of film thickness on photocatalytic activity was also discussed.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. TEM investigation of irradiation damage in single crystal CeO 2

    NASA Astrophysics Data System (ADS)

    Ye, Bei; Kirk, Mark A.; Chen, Weiying; Oaks, Aaron; Rest, Jeffery; Yacout, Abdellatif; Stubbins, James F.

    2011-07-01

    In order to understand the evolution of radiation damage in oxide nuclear fuel, 150-1000 keV Kr ions were implanted into single crystal CeO 2, as a simulation of fluorite ceramic UO 2, while in situ transmission electron microscopy (TEM) observations were carried out. Two characteristic defect structures were investigated: dislocation/dislocation loops and nano-size gas bubbles. The growth behavior of defect clusters induced by 1 MeV Kr ions up to doses of 5 × 10 15 ions/cm 2 were followed at 600 °C and 800 °C. TEM micrographs clearly show the development of defect structures: nucleation of dislocation loops, transformation to extended dislocation lines, and the formation of tangled dislocation networks. The difference in dislocation growth rates at 600 °C and 800 °C revealed the important role which Ce-vacancies play in the loop formation process. Bubble formation, studied through 150 keV Kr implantations at room temperature and 600 °C, might be influenced by either the mobility of metal-vacancies correlated with at threshold temperature or the limitation of gas solubility as a function of temperature.

  12. Study of dielectric properties of Ca doped barium titanate ceramics

    NASA Astrophysics Data System (ADS)

    Pradhan, S. K.; Kumar, Amit; Sinha, A. N.; Kour, P.

    2016-05-01

    Ba1-xCax Zr0.52Ti0.48 O3 ceramics was prepared by sol gel method. The crystallite size was in nano scale range. The dielectric constant was increased with increase in Ca2+ concentration in the sample. The dielectric loss was decreased with increase in ca concentration in the sample. The ac conductivity of the sample was increased with increase in Ca2+ concentration in the sample. The ac conductivity of the sample follows Johnscher power law. AC conductivity analysis shows that the interactions between neighbouring dipoles were decreased with the increase in Ca2+ concentration in the sample.

  13. 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.

  14. Ultrahigh temperature Bi3Ti0.96Sc0.02Ta0.02NbO9-based piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Gai, Zhi-Gang; Wang, Jin-Feng; Sun, Wen-bin; Wang, Chun-Ming; Zhao, Ming-Lei; Sun, Shang-Qian; Ming, Bao-Quan; Qi, Peng; Zheng, Li-mei; Du, Juan; Zhang, Shujun; Shrout, Thomas R.

    2008-07-01

    The effect of (Sc,Ta,Ce) doping on the properties of Bi3TiNbO9 (BTNO)-based ceramics was investigated. The cerium modification greatly improves the piezoelectric activity of Bi3(Ti0.96Sc0.02Ta0.02)NbO9-based ceramics and significantly decreases the dielectric dissipation. The d33 of Bi3Ti0.96Sc0.02Ta0.02NbO9+x wt %CeO2 (x =0.35) was found to be 18 pC/N, the highest value among the BTNO-based ceramics and almost three times as much as the reported d33 values of the pure BTNO ceramics (˜6 pC/N). The modification increased the resistivity ρ of the samples extremely, resolving the low resistivity problem for high temperature applications. The dielectric spectroscopy shows that the TC for all the ceramics is higher than 900 °C. The mechanical quality factor Q and planar coupling factors kp and kt of Bi3Ti0.96Sc0.02Ta0.02NbO9+0.35 wt %CeO2 ceramic were found to be 2835, 9%, and 23%, respectively, and it has high TC and stable piezoelectric properties, demonstrating that the (Sc,Ta,Ce) modified BTNO-based material is a wonderful candidate for high temperature applications.

  15. 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

  16. 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

  17. 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

  18. Electrochromic performance of sol-gel-deposited CeO2 films

    NASA Astrophysics Data System (ADS)

    Ozer, Nilgun; Cronin, John P.; Akyuz, Sevim

    1999-10-01

    Ceria (CeO2) films were prepared by a sol-gel technique onto fluorine doped tin oxide coated glass substrates. The coating solution was derived from cerium ammonium nitrate dissolved in ethanol with diethanolamine used as a complexing agent. Lithium intercalating properties of the films were investigated using cyclic voltammetry (CV) and UV-visible spectroscopy. The electrochemical examinations were performed in a 0.5 M LiClO4 propylene carbonate electrolyte. The additional film characterizations were performed in X-ray diffractometry (XRD), x-ray photoelectron spectroscopy, scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy. XRD of the films showed that they had an cerianite structure for heat treatment temperatures at or above 450 degree(s)C. The SEM examinations showed that the surface texture was uniform and homogeneous. CV examinations showed a reversible electrochemical insertion or extraction of Li+/e- ions maintaining a high optical transmissivity. Spectroelectrochemistry showed that these films can be used as optically passive counter-electrode in transmissive electrochromic devices.

  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. 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.

  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. 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.

  4. Diffuse phase transition of Fe doped lead ytterbium tantalate ceramics

    NASA Astrophysics Data System (ADS)

    Rout, Dibyaranjan; Subramanian, V.; Hariharan, K.; Sivasubramanian, V.

    2006-02-01

    The effect of different concentration of Fe on the phase transition behavior of Lead ytterbium tantalate is investigated by dielectric and differential scanning calrimetry measurements. The samples are prepared through solid state reaction method and it has been found that the sintering temperature significantly lowered when the proportion of Pb(Fe 1/2Ta 1/2)O 3 increased. It has been observed that the doping in small amounts (0≤ x≤0.2) of Fe could meliorate the dielectric and ferroelectric properties. The diffuseness in the mode of phase transition increases and the phase transition temperature decreases as a function of Fe content. It is revealed that the dielectric data and heat capacity data follow a similar trend in the variation of the mode of phase transition and phase transition temperatures. The phase transition temperature values obtained from the heat capacity measurement well agreed with the values obtained from dielectric measurement.

  5. Eu doping in multiferroic BiFeO3 ceramics studied by Mossbauer and EXAFS spectroscopy.

    PubMed

    Kothari, Deepti; Raghavendra Reddy, V; Gupta, Ajay; Meneghini, Carlo; Aquilanti, Giuliana

    2010-09-01

    Bismuth ferrite ceramics (BiFeO(3)) are multifunctional materials classified as multiferroics for their special magnetic and electric properties that can be modified by substitutional doping at the Bi and/or Fe sites. Understanding the relation between magnetoelectric response and structural/electronic modification upon doping is a relevant issue. In this work, the structure of Eu-doped multiferroic systems (Bi(1-x)Eu(x)FeO(3), x = 0, 0.5, 0.1, 0.15) as well as the valence state of Fe and Eu ions have been investigated combining Mossbauer and x-ray absorption fine structure (XAFS) spectroscopy techniques. The Eu(3+) doping at the Bi site results in better magnetic properties. High temperature (57)Fe Mossbauer data and Fe K-edge XAFS results show that FeO(6) octahedron distortions reduce with Eu(3+) doping. It is conclusively shown that the observed magnetic properties in BiFeO(3) with chemical substitution (Eu) are mainly due to the structural distortions and not due to Fe multiple valence. (151)Eu Mossbauer measurements show that the Eu(3+)(Bi(3+)) site is magnetically inactive in BiFeO(3). PMID:21403301

  6. Eu doping in multiferroic BiFeO3 ceramics studied by Mossbauer and EXAFS spectroscopy

    NASA Astrophysics Data System (ADS)

    Kothari, Deepti; Raghavendra Reddy, V.; Gupta, Ajay; Meneghini, Carlo; Aquilanti, Giuliana

    2010-09-01

    Bismuth ferrite ceramics (BiFeO3) are multifunctional materials classified as multiferroics for their special magnetic and electric properties that can be modified by substitutional doping at the Bi and/or Fe sites. Understanding the relation between magnetoelectric response and structural/electronic modification upon doping is a relevant issue. In this work, the structure of Eu-doped multiferroic systems (Bi1 - xEuxFeO3, x = 0, 0.5, 0.1, 0.15) as well as the valence state of Fe and Eu ions have been investigated combining Mossbauer and x-ray absorption fine structure (XAFS) spectroscopy techniques. The Eu3 + doping at the Bi site results in better magnetic properties. High temperature 57Fe Mossbauer data and Fe K-edge XAFS results show that FeO6 octahedron distortions reduce with Eu3 + doping. It is conclusively shown that the observed magnetic properties in BiFeO3 with chemical substitution (Eu) are mainly due to the structural distortions and not due to Fe multiple valence. 151Eu Mossbauer measurements show that the Eu3 + (Bi3 + ) site is magnetically inactive in BiFeO3.

  7. 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.

  8. Effect of Fe doping on structural and impedance properties of PZTFN ceramics

    NASA Astrophysics Data System (ADS)

    Kumar, Arvind; Pal, Vijayeta; Mishra, S. K.

    2016-05-01

    An attempts have been made to synthesis the ceramics Pb1-3x/2 Fex(Zr0.52Ti0.48)1-5y/4 NbyO3 abbreviated as (PFZTN) for x = 1-6 mol% and y = 5.5 mol% by a semi-wet route. In the present paper, we have investigated the effect of Fe doping on structural and electrical properties of the PFZTN ceramics. X-ray diffraction (XRD) patterns reveal that PFZTN ceramics are single phase in nature. However, for x = 0.05 and 0.06, a secondary phase appears as discernible from the XRD profiles. Rietveld analysis of the powder diffraction data shows the presence of coexistence of tetragonal (P4mm space group) and rhombohedral phases (R3c space group) occurs near the morphotropic phase boundary (MPB) at x ≥ = 0.05. The log-log plots show that the conductivity increases with increase of temperature. The ac conductivity becomes sensitive at high frequency region and shifted towards higher frequency side with increasing temperature. It is observed that the activation energy (Ea) decreases with increasing frequency. This complex perovskite structure can be used as a multilayer ceramic capacitors and electromechanical transducers.

  9. Luminescence study of mixed valence Eu-doped nanocrystalline glass-ceramics

    NASA Astrophysics Data System (ADS)

    Bagga, Ruchika; Achanta, Venu Gopal; Goel, Ashutosh; Ferreira, José M. F.; Singh, Narinder Pal; Singh, Davinder Paul; Contini, Vittoria; Falconieri, Mauro; Sharma, Gopi

    2013-12-01

    Eu-doped nanocrystalline NaAlSiO4/NaY9Si6O26 glass-ceramics have been prepared by controlled crystallization of melt quenched bulk glasses. XRD, SEM and FTIR spectroscopy techniques were employed to characterize the crystallization process and the structural properties of the precursor glass and corresponding glass-ceramics. The formation of divalent europium (Eu2+) from Eu3+ ions during high temperature synthesis under ambient atmosphere was analyzed by photoluminescence spectroscopy and is discussed using the optical basicity model. The observed luminescence properties of Eu: NaY9Si6O26 are compared with that of Eu: β-PbF2 nanocrystals and their marked differences are discussed.

  10. 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.

  11. 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.

  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. 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.

  14. Structural, topographical and electrical properties of cerium doped strontium barium niobate (Ce:SBN60) ceramics

    NASA Astrophysics Data System (ADS)

    Raj, S. Gokul; Mathivanan, V.; Kumar, G. Ramesh; Yathavan, S.; Mohan, R.

    2016-05-01

    Tungsten bronze type cerium doped strontium barium niobate (Ce:SBN - Sr0.6B0.4Nb2O6) ceramics were synthesized by solid state process. Cerium was used as dopant to improve its electrical properties. Influence of Ce+ ions on the photoluminescence properties was investigated in detail. The grain size topographical behavior of SBN powders and their associated abnormal grain growth (AGG) were completely analyzed through SEM studies. Finally dielectric, measurement discusses about the broad phase transition observed due to cerium dopant The results were discussed in detail.

  15. 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

  16. Luminescence of Er/Yb and Tm/Yb doped FAp nanoparticles and ceramics

    NASA Astrophysics Data System (ADS)

    Grigorjeva, L.; Smits, K.; Millers, D.; Jankoviča, Dz

    2015-03-01

    The nanoparticles of hydroxiapatite and fluorapatite doped with Er/Yb and Tm/Yb were synthesized and characterized by FTIR, XRD, SEM and TEM methods. The results of up-conversion luminescence studies were presented for the samples as prepared, annealed at 500°C and at 900-1000 °C. At annealing above 800°C the ceramic state was formed. It is shown that fluorapatite host is more appropriate than hydroxiapatite host for rare ions luminescence and up-conversion processes. The post preparing annealing of nanarticles significantly enhanced the luminescence intensity. The Tm/Yb doped fluorapatite shows intense up-conversion luminescence in 790-800 nm spectral region and is potentially useful for biomedical applications.

  17. 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.

  18. Structural and optical properties of Pr doped BiFeO3 multiferroic ceramics

    NASA Astrophysics Data System (ADS)

    Singh, Vikash; Subhash, Dwivedi, R. K.; Kumar, Manoj

    2013-02-01

    Pure and Pr substituted BiFeO3 (BFO) ceramics were synthesized by solid state reaction method. X-ray analysis shows the formation of BFO rhombohedral phase with R3c space group. Photoluminescent spectra of pure BFO showed blue emission corresponding to band gap at 2.67 eV. In Pr doped samples in addition to blue emission (2.67eV), a broad weak yellow emission has also been observed due to electronic transitions of dopant Pr3+ states. FTIR spectra showed two broad absorption peaks due to overlapping of Fe-O and Bi-O groups in the region 700 - 400 cm-1. These interesting optical properties of Pr doped BFO samples in visible region may find potential applications in optoelectronic devices.

  19. 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.

  20. Strong red emission in Pr doped (Bi0.5Na0.5)TiO3 ferroelectric ceramics

    NASA Astrophysics Data System (ADS)

    Sun, Haiqin; Peng, Dengfeng; Wang, Xusheng; Tang, Mianmian; Zhang, Qiwei; Yao, Xi

    2011-07-01

    The photoluminescence of Pr doped (Bi0.5Na0.5)TiO3 ferroelectric ceramics prepared by conventional solid-state reaction were investigated. A bright red emission is observed at room temperature, which ascribed to 1D2→3H4 transition. The excitation bands are mainly located at 440 ˜ 505 nm, which is adaptable to the emission band of commercial blue light-emitting diodes (LEDs) chips. The optimal emission intensity was also obtained when Pr doping level was 0.003 mol. Meanwhile, the enhanced ferroelectric properties were obtained by Pr doping. The results show that Pr doped (Bi0.5Na0.5)TiO3 ceramics as a multifunctional material may be useful for white LEDs, sensor, and optical-electro integration.

  1. Influence of Zr4+ doping on structural and electrical properties of SrBi4Ti4O15 ceramic

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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 SrBi4Ti4-xZrxO15 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.

  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. Broadband mid-infrared wavelength conversion laser based on Cr2+ doped ceramic materials

    NASA Astrophysics Data System (ADS)

    Shang, Yaping; Yin, Ke; Li, Xiao; Wang, Peng; Xu, Xiaojun

    2015-10-01

    Broadband mid-infrared lasers are desirable for pretty important applications in fields of environmental protection, medical treatment, military applications, scientific, and other domains. Recently, super-continuum laser sources have achieved striking development. However, limited by the substrate materials, the output power scaling of the broadband mid-infrared fiber laser sources could not be increased drastically, especially for the long wavelength region. In this paper, we reported an experimental study about the broadband mid-infrared lasers based on Cr2+ doped II-VI ceramic materials, by using of a super-continuum laser source developed by our groups operating at 1550~2130nm with 200mW output power. The result suggested that the near-infrared spectral component of the super-continuum source was deeply absorbed by transition metal doped zinc chalcogenides ceramic materials, meanwhile the mid-infrared part, however, had been enhanced significantly by this new "power amplifier." Actually single-pass amplification efficiency was very limited. The best way to solve this problem was multi-pass amplification systems. We had shown an initial proof of this assumption by a double-pass experiments, the result was consistent with expected effect. Above all, the spectrum shaping from short wavelength to long wavelength was obtained. The innovative discovery had laid a solid foundation for high power, high efficiency, broadly tunable mid-infrared solid state lasers.

  4. 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

  5. Enzymatic glucose biosensor based on CeO2 nanorods synthesized by non-isothermal precipitation.

    PubMed

    Patil, Dewyani; Dung, Nguyen Quoc; Jung, Hyuck; Ahn, Se Yong; Jang, Dong Mi; Kim, Dojin

    2012-01-15

    Cerium oxide nanorods (CeO(2) NRs) were synthesized without templates through a low cost and simple non-isothermal precipitation method. The structure and morphology of CeO(2) NRs were characterized by X-ray diffraction and transmission electron microscopy. The CeO(2) NRs films, deposited on indium tin oxide (ITO)-coated glass substrates through electrophoretic deposition, were used for the immobilization of glucose oxidase (GOx). Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were used to characterize the CeO(2) NRs/ITO and GOx/CeO(2) NRs/ITO electrodes. The GOx/CeO(2) NRs/ITO electrode exhibits a linear range for the detection of glucose from 2 to 26 mM (correlation coefficient: 0.99) at 1-2s response time. Biosensor sensitivity is 0.165 μA mM(-1) cm(-2) with 100 μM detection limit. The anti-interference ability of the biosensor was also examined. The mediator-less application of CeO(2) NRs for glucose sensing was demonstrated. PMID:22035972

  6. Single-step process to prepare CeO2 nanotubes with improved catalytic activity.

    PubMed

    González-Rovira, Leandro; Sánchez-Amaya, José M; López-Haro, Miguel; del Rio, Eloy; Hungría, Ana B; Midgley, Paul; Calvino, José J; Bernal, Serafín; Botana, F Javier

    2009-04-01

    CeO(2) nanotubes have been grown electrochemically using a porous alumina membrane as a template. The resulting material has been characterized by means of scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy, high-angle annular dark-field scanning transmission electron microscopy tomography, high-resolution electron microscopy (HREM), and electron energy loss spectroscopy. According to SEM, the outer diameter of the nanotubes corresponds to the pore size (200 nm) of the alumina membrane, and their length ranges between 30 and 40 microm. HREM images have revealed that the width of the nanotube walls is about 6 nm. The catalytic activity of these novel materials for the CO oxidation reaction is compared to that of a polycrystalline powder CeO(2) sample prepared by a conventional route. The activity of the CeO(2) nanotubes is shown to be in the order of 400 times higher per gram of oxide at 200 degrees C (77.2 x 10(-2) cm(3) CO(2) (STP)/(gxs) for the nanotube-shaped CeO(2) and 0.16 x 10(-2) cm(3) CO(2) (STP)/(gxs) for the powder CeO(2)). PMID:19245236

  7. 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

  8. 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

  9. Raman and impedance spectroscopic studies of the specific features of the transport properties of electrolytes based on CeO2

    NASA Astrophysics Data System (ADS)

    Sal'nikov, V. V.; Pikalova, E. Yu.

    2015-10-01

    The solid solutions CeO2-(Sm,Nd)2O3 have been prepared by the solid-phase synthesis. The microstructure, density, and electrical conductivity of ceramic samples obtained by rolling with an organic binder, followed by sintering in air at a temperature of 1600°C have been investigated. The contributions to the total conductivity from the grain volume and grain boundaries in the temperature range of 250-700°C have been separated using impedance spectroscopy. The impedance spectroscopy data have revealed a significant effect of grain boundaries on the transport properties of the solid electrolyte with a Sm dopant as compared to the electrolyte with Nd. The optical properties of the polycrystalline electrolytes Ce1- x Nd x O2-δ and Ce0.8Sm0.2O2-δ have been studied using Raman spectroscopy. In the spectrum of the ceramic samples, there are two modes: a mode of CeO2 at a frequency of 465 cm-1 and an additional mode at a frequency of ~550 cm-1 due to vibrations associated with oxygen vacancies, the intensity of which depends on the dopant concentration and the energy of the dopant cation-oxygen vacancy bond. The binding energy of oxygen vacancies in the fluorite structure correlates with the behavior of bulk conductivity, and the solid solutions with samarium exhibit the highest bulk conductivity.

  10. 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. PMID:27067736

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  12. 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.

  13. Effect of fabrication routes on the properties of Mn-doped BaTi2O5 ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Wenfeng; Tsukada, Shinya; Akishige, Yukikuni

    2014-01-01

    In the present study, 0, 0.2, and 0.4 wt % MnO2 doped BaTi2O5 ceramics were fabricated by three different routes, i.e., sol-gel deriving powders and spark plasma sintering (SPS) sintering, solid state calcining and SPS sintering, sol-gel deriving powders and two times sintering. Only through the sol-gel technique and conventional sintering route, Mn could substitute for Ti as the acceptor doping and consequently caused the sharp drop of the Curie temperature as well as the enhanced dielectric constant and restricted ferroelectricity. Besides, the 0.2 wt % MnO2 doped BaTi2O5 ceramics fabricated by sol-gel deriving powders and SPS sintering exhibited the most superior dielectric and ferroelectric properties.

  14. Pressureless sintering of plasma-reacted nanosemicrystalline silicon nitride ceramics with doped sintering additives

    NASA Astrophysics Data System (ADS)

    Ryu, Kevin Hojun

    For the past few years, synthesis and consolidation of ceramics using nanoparticles have been a focus of much research. The obvious advantage is their low process temperatures (<200°C). In addition, the process results in super-plastic deformation, and drastically enhances the mechanical properties of the ceramics. Recently, a plasma-assisted chemical reaction was adopted to produce nanosize Si3N4 powders that have the characteristics of sintering additive elements on individual particles. Homogeneous size distribution of the additives can eliminate inhomogeneous shrinkage of the sintered body during the mixing process. In this work, the behavior of plasma-reacted nano-size Si3N 4 powders intrinsically doped with sintering additives was explored. These particles were doped with Y2O3 and Al2O 3, and processed under a low process temperature in the absence of pressurizing equipment. Several experiments were performed to address the effects of the powders on the phase transformation rate from a to b phase, and on the mechanical properties due to the microstructure evolution under different sintering conditions. The existence of sintering additive elements in each individual powder was verified by electron microscope and energy dispersive spectroscopy. The doped powders were 60% crystalline and had a specific surface area of ˜24 m2/g. The powders showed excellent sinterability at low temperature, compared to the other powders used in commercial processes. In spite of the low process temperature, the a→ b phase transformation occurred rapidly. The homogeneous distribution of Si3N4 powders was speculated as the reason for fast phase transformation. In addition, evolution of the microstructures in different sintering conditions produced materials with vastly different mechanical properties. Thus, one may obtain ceramics with desired mechanical properties by carefully controlling the sintering additives. Finally, a mathematical model, based on the previous work done by

  15. 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

  16. Fabrication of rod-like CeO 2: Characterization, optical and electrochemical properties

    NASA Astrophysics Data System (ADS)

    Zhang, Dong-En; Ni, Xiao-Min; Zheng, Hua-Gui; Zhang, Xiao-Jun; Song, Ji-Mei

    2006-11-01

    One-dimensional CeO 2 nanoparticles were obtained via the thermal treatment of cerium oxalate nanorods, which were synthesized through a convenient precipitation route. The morphology of the precursor was maintained during the heating process, while the size of the subunits was tailored by adjusting the calcining temperature. The optical absorption spectrum indicates that the direct band gaps of CeO 2 decreases from 3.95 to 3.86 eV as the calcination temperature increases from 500 to 800 °C. Thus-prepared nanostructured CeO 2 with subunits of about 15 nm exhibited a first discharge specific capacity of 574 mAh g -1 vs. Li metal, much higher than that of the sample with bigger building blocks (30 nm, 519 mAh g -1).

  17. 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.

  18. 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.

  19. 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)

  20. Oxygen vacancy formation in CeO2 and Ce(1-x)Zr(x)O2 solid solutions: electron localization, electrostatic potential and structural relaxation.

    PubMed

    Wang, Hai-Feng; Li, Hui-Ying; Gong, Xue-Qing; Guo, Yang-Long; Lu, Guan-Zhong; Hu, P

    2012-12-28

    Ceria (CeO(2)) and ceria-based composite materials, especially Ce(1-x)Zr(x)O(2) solid solutions, possess a wide range of applications in many important catalytic processes, such as three-way catalysts, owing to their excellent oxygen storage capacity (OSC) through the oxygen vacancy formation and refilling. Much of this activity has focused on the understanding of the electronic and structural properties of defective CeO(2) with and without doping, and comprehending the determining factor for oxygen vacancy formation and the rule to tune the formation energy by doping has constituted a central issue in material chemistry related to ceria. However, the calculation on electronic structures and the corresponding relaxation patterns in defective CeO(2-x) oxides remains at present a challenge in the DFT framework. A pragmatic approach based on density functional theory with the inclusion of on-site Coulomb correction, i.e. the so-called DFT + U technique, has been extensively applied in the majority of recent theoretical investigations. Firstly, we review briefly the latest electronic structure calculations of defective CeO(2)(111), focusing on the phenomenon of multiple configurations of the localized 4f electrons, as well as the discussions of its formation mechanism and the catalytic role in activating the O(2) molecule. Secondly, aiming at shedding light on the doping effect on tuning the oxygen vacancy formation in ceria-based solid solutions, we summarize the recent theoretical results of Ce(1-x)Zr(x)O(2) solid solutions in terms of the effect of dopant concentrations and crystal phases. A general model on O vacancy formation is also discussed; it consists of electrostatic and structural relaxation terms, and the vital role of the later is emphasized. Particularly, we discuss the crucial role of the localized structural relaxation patterns in determining the superb oxygen storage capacity in kappa-phase Ce(1-x)Zr(1-x)O(2). Thirdly, we briefly discuss some

  1. 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.

  2. 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.

  3. [The research on preparing CeO2 nanocrystalline by homogeneous precipitation method].

    PubMed

    Garidi; Li, Xia; Li, Li; Zhaorigetu

    2006-09-01

    CeO2 nanocrystallines were prepared by homogeneous complexed-precipitation method, using cerous nitrate and ammonium tartrate as raw materials. The effects of cerous tartrate complex compound and the way of producing precipitation on the particle size of samples were investigated. The samples were characterized by XRD, TEM and SEM. The SEM micrograph shows that the foam exhibits a perforated porousness stereostructure in shape, and the HRTEM picture of the particles reveals the clear crystal lattice. All the results indicate that the samples were CeO2 nanocrystalline. PMID:17112061

  4. 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.

  5. 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.

  6. Spectroscopic and dielectric investigations of tungsten ions doped zinc bismuth phosphate glass-ceramics

    NASA Astrophysics Data System (ADS)

    Srinivasa Rao, P.; Bala Murali Krishna, S.; Yusub, S.; Ramesh Babu, P.; Tirupataiah, Ch.; Krishna Rao, D.

    2013-03-01

    Pure and tungsten oxide doped ZnF2sbnd Bi2O3sbnd P2O5 glass-ceramics are prepared by the melt quenching and heat treatment techniques. These samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS) and differential thermal analysis (DTA) techniques. The X-ray diffraction and the scanning electron microscopic studies have revealed the presence of BiPO4, α-Zn3(PO4)2, α-Zn(PO3)2, Zn3(PO4)2, WOF4, WOPO4, γ-Bi2WO6, Bi2W2O9, microcrystalline phases in these samples. FTIR and Raman studies exhibit bands due WO4 and WO6 units along with conventional phosphate groups. The optical absorption and electron spin resonance (ESR) spectra of present glass-ceramics indicate the co-existence of both W5+ and W6+ ions. The analysis of dielectric properties (dielectric constant, loss tan δ, a.c. conductivity) over a range of frequency and temperature suggests a gradual increase in semi conducting character with increase in the concentration of WO3. The studies on dielectric breakdown strength indicated the lowest insulating strength for 5.0 mol% of WO3 in the present samples.

  7. Formation of nanostructures in Eu3+ doped glass-ceramics: an XAS study

    NASA Astrophysics Data System (ADS)

    Pellicer-Porres, J.; Segura, A.; Martínez-Criado, G.; Rodríguez-Mendoza, U. R.; Lavín, V.

    2013-01-01

    We describe the results of x-ray absorption experiments carried out to deduce structural and chemical information in Eu3+ doped, transparent, oxyfluoride glass and nanostructured glass-ceramic samples. The spectra were measured at the Pb and Eu-LIII edges. The Eu environment in the glass samples is observed to be similar to that of EuF3. Complementary x-ray diffraction experiments show that thermal annealing creates β-PbF2 type nanocrystals. X-ray absorption indicates that Eu ions act as seeds in the nanocrystal formation. There is evidence of interstitial fluorine atoms around Eu ions as well as Eu dimers. X-ray absorption at the Pb-LIII edge shows that after the thermal treatment most lead atoms form a PbO amorphous phase and that only 10% of the lead atoms remain available to form β-PbF2 type nanocrystals. Both x-ray diffraction and absorption point to a high Eu content in the nanocrystals. Our study suggests new approaches to the oxyfluoride glass-ceramic synthesis in order to further improve their properties.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. Influence of lanthanum doping on the dielectric, ferroelectric and relaxor behaviour of barium bismuth titanate ceramics

    NASA Astrophysics Data System (ADS)

    Kumar, Sunil; Varma, K. B. R.

    2009-04-01

    Barium lanthanum bismuth titanate (Ba1-(3/2)xLaxBi4Ti4O15, x = 0-0.4) ceramics were fabricated using the powders synthesized via the solid-state reaction route. X-ray powder diffraction analysis confirmed the above compositions to be monophasic and belonged to the m = 4 member of the Aurivillius family of oxides. The effect of the partial presence of La3+ on Ba2+ sites on the microstructure, dielectric and relaxor behaviour of BaBi4Ti4O15 (BBT) ceramics was investigated. For the compositions pertaining to x <= 0.1, the dielectric constant at both room temperature and in the vicinity of the temperature of the dielectric maximum (Tm) of the parent phase (BBT) increased significantly with an increase in x while Tm remained almost constant. Tm shifted towards lower temperatures accompanied by a decrease in the magnitude of the dielectric maximum (ɛm) with an increase in the lanthanum content (0.1 < x <= 0.4). The dielectric relaxation was modelled using the Vogel-Fulcher relation and a decrease in the activation energy for frequency dispersion with increasing x was observed. The frequency dispersion of Tm was found to decrease with an increase in lanthanum doping, and for compositions corresponding to x >= 0.3, Tm was frequency independent. Well-developed P(polarization)-E(electric field) hysteresis loops were observed at 150 °C for all the samples and the remanent polarization (2Pr) was improved from 6.3 µC cm-2 for pure BBT to 13.4 µC cm-2 for Ba0.7La0.2Bi4Ti4O15 ceramics. Dc conductivities and associated activation energies were evaluated using impedance spectroscopy.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Zuo, Chendong

    A worldwide energy crisis and increasing environmental concerns are strong incentives for using hydrogen as a sustainable and clean energy source. "Hydrogen economy" has been around since 1970s, but it started to look practicable only in recent years. The trend in the future is to switch from using hydrogen as the basic raw material in the chemical industry to the energy carrier in the transportation and distributed energy industries. To meet the expected rising demand, hydrogen has to be generated in a more cost-effective manner. As one of the most important operation units in the hydrogen production, a high performance hydrogen separation membrane system is essential to the coming hydrogen economy. The project of hydrogen separation membrane based on Mixed ionic and electronic conductor (MIEC) composite was initiated by DoE years ago, and the MIEC membrane has been developed in Argonne National Laboratory (ANL) for several years. The goal at ANL is to develop a dense, ceramic-based MIEC membrane that is highly selective, chemical stable in practical environments at operative temperatures up to ≈900°C, and can separate hydrogen from mixed gases at commercially significant fluxes under industrially relevant operating conditions, without the need for electrodes or electrical circuitry. The effort at ANL initially focused on BCY20 (BaCe0.8Y 0.2O3). BCY20 forms the matrix of ANL-1a and -2a ceramic-metal composite membranes (40-50 vol.% of a metal is dispersed in a ceramic matrix) and its bulk transport properties, including ionic transfer number, ionic and electronic conductivity, and chemical and mechanical stability have been systematically studied. However, exposure to CO2 and H2O-containing atmospheres, as would be present in a practical environment, will degrade the material as it reacts to form insulating barium carbonate (BaCO3 ) and cerium oxide (CeO2). This decomposition greatly limits its applicability in hydrogen separation, despite the promising

  15. 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.

  16. Boron-Doped Strontium-Stabilized Bismuth Cobalt Oxide Thermoelectric Nanocrystalline Ceramic Powders Synthesized via Electrospinning

    NASA Astrophysics Data System (ADS)

    Koçyiğit, Serhat; Aytimur, Arda; Çınar, Emre; Uslu, İbrahim; Akdemir, Ahmet

    2014-01-01

    Boron-doped strontium-stabilized bismuth cobalt oxide thermoelectric nanocrystalline ceramic powders were produced by using a polymeric precursor technique. The powders were characterized by using x-ray diffraction (XRD), scanning electron microscopy (SEM), and physical properties measurement system (PPMS) techniques. The XRD results showed that these patterns have a two-phase mixture. The phases are face-centered cubic (fcc) and body-centered cubic (bcc). Values of the crystallite size, dislocation density, and microstrain were calculated by using the Scherrer equation. The lattice parameters were calculated for fcc and bcc phases. The SEM results showed that needle-like grains are formed in boron-undoped composite materials, but the needle-like grains changed to the plate-like grains with the addition of boron. The distribution of the nanofiber diameters was calculated and the average diameter of the boron-doped sample is smaller than the boron-undoped one. PPMS values showed that the electrical resistivity values decreased, but the thermal conductivity values, the Seebeck coefficients, and figure of merit ( ZT) increased with increasing temperature for the two samples.

  17. 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%.

  18. 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.

  19. 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.

  20. 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

  1. 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. PMID:27120134

  2. Study of the growth of CeO2 nanoparticles onto titanate nanotubes

    NASA Astrophysics Data System (ADS)

    Marques, Thalles M. F.; Ferreira, Odair P.; da Costa, Jose A. P.; Fujisawa, Kazunori; Terrones, Mauricio; Viana, Bartolomeu C.

    2015-12-01

    We report the study of the growth of CeO2 nanoparticles on the external walls and Ce4+ intercalation within the titanate nanotubes. The materials were fully characterized by multiple techniques, such as: Raman spectroscopy, infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The ion exchange processes in the titanate nanotubes were carried out using different concentrations of Ce4+ in aqueous solution. Our results indicate that the growth of CeO2 nanoparticles grown mediated by the hydrolysis in the colloidal species of Ce and the attachment onto the titanate nanotubes happened and get it strongly anchored to the titanate nanotube surface by a simple electrostatic interaction between the nanoparticles and titanate nanotubes, which can explain the small size and even distribution of nanoparticles on titanate supports. It was demonstrated that it is possible to control the amount and size of CeO2 nanoparticles onto the nanotube surface, the species of the Ce ions intercalated between the layers of titanate nanotubes, and the materials could be tuned for using in specific catalysis in according with the amount of CeO2 nanoparticles, their oxygen vacancies/defects and the types of Ce species (Ce4+ or Ce3+) present into the nanotubes.

  3. Coadsorption of gold with chlorine on CeO2 (111) surfaces: A first principles study

    NASA Astrophysics Data System (ADS)

    Lu, Zhan-Sheng; He, Bing-Ling; Ma, Dong-Wei; Yang, Zong-Xian

    2015-02-01

    To investigate the effects of chlorine on the Au/ceria catalysts, the adsorption of gold or chlorine and their coadsorpiton on the stoichiometric and partially reduced CeO2 (111) surfaces are studied from the first principles. It is found that the adsorption of Au is significantly enhanced by the chlorine preadsorption on the stoichiometric CeO2 (111) surface; while on the partially reduced CeO2 (111) surface, the preadsorbed chlorine inhabits the oxygen vacancy (which is the preferred adsorption site for gold), leading to a CeOCl phase and the dramatical weakening of the Au adsorption. Therefore, chlorine on the CeO2 (111) surface can affect the Au adsorption thus the activity of the Au/CeO2 catalyst. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174070, 51401078, and 11147006), the China Postdoctoral Science Foundation (Grant No. 2012M521399), the Postdoctoral Research Sponsorship in Henan Province, China (Grant No. 2011038), and the Foundation for the Key Young Teachers of Henan Normal University and Start-up Foundation for Doctors of Henan Normal University, China.

  4. Low temperature environmental degradation of zirconia ceramics

    NASA Astrophysics Data System (ADS)

    Zhao, Zhenbo

    2005-11-01

    The low temperature environmental degradation (LTED) of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) has been prevented, or at least retarded, by using both bulk doping and surface doping methods with either cation, or anion, stabilizers. The introduction of both mullite and alumina into 3Y-TZP by a bulk-doping method was found to be effective in suppressing the tetragonal-->monoclinic transformation induced by water during hydrothermal treatment thus giving rise to better mechanical properties. The beneficial effects of alumina on the phase stability of the 3Y-TZP ceramic are considered to be due to the increase in the elastic modulus of the constraining matrix, as well as to the segregation of A12O3 at grain boundaries. The LTED transformation kinetics as determined by x-ray diffraction (XRD) and White Light Interferometer (WLI) analysis showed that the isothermal tetragonal-to-monoclinic transformation starts from the surface and has an incubation-nucleation-growth mechanism which can be described by the Johnson-Mehl-Avrami equation. The degradation of Y-TZP ceramic after hydrothermal treatment can be effectively overcome by surface doping by a solid diffusion method with tetravalent dopants: CeO2 and GeO2; with trivalent dopants: La2O 3 and Fe2O3; and with divalent dopants: CuO and MgO. For surface CeO2-, GeO2- and Fe2O 3-doping, this degradation inhibition behaviour is attributed to a localized increase in cation stabilizer content which satisfies the requirements for stabilization of the tetragonal phase. However, in each case, the stability mechanisms are different. For surface La2O3doping, surface doping overcomes the formation of La2O3 and La 2Zr2O7 since the extra La2O3 can further diffuse to the center of the 3Y-TZP ceramic. For CuO-doping, small amounts of CuO form a liquid that can act as a conduit for the re-distribution of yttria. In the case of surface MgO modification, the stabilization results from the isolated nature of the

  5. 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 ...

  6. 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.

  7. 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. PMID:26461912

  8. 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.

  9. 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.

  10. Random lasing in Eu3+ doped borate glass-ceramic embedded with Ag nanoparticles under direct three-photon excitation

    NASA Astrophysics Data System (ADS)

    Xu, Xuhui; Zhang, Wenfei; Jin, Limin; Qiu, Jianbei; Yu, Siu Fung

    2015-10-01

    We report the observation of random lasing from Eu3+ 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 Eu3+ 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.

  11. 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

  12. Up-conversion luminescence from Er3+, Yb3+ co-doped GeO II-PbF II-Nb IIO 5 glass ceramic

    NASA Astrophysics Data System (ADS)

    Lv, Jinwen; Sang, Lanfen; Zhang, Jing; Fu, Xingguo

    2006-01-01

    The paper reports a new up-conversion luminescence material based on Yb 3+, Er 3+ co-doped germanate glass ceramic, the matrix system is GeO II-PbF II-Nb IIO 5. The luminescence characteristics of the Yb3+ , Er3+ co-doped glass ceramic have been studied. The structural properties of the germinate glass ceramic have been analysed by X-ray diffraction. Under the condition of 980nm semiconductor laser pumping, the green fluorescence intensity shows that the existence of niobate components plays an important role for up-conversion luminescence.

  13. 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.

  14. 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.

  15. 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.

  16. 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%.

  17. Room-Temperature Magnetocapacitance in Fe-Doped K0.5Na0.5Nb0.95Ta0.05O3 Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Huan; Yang, Wenlong; Li, Yu; Meng, Qingxin; Zhou, Zhongxiang

    2012-10-01

    Ferroelectric and magnetic properties of Fe-doped potassium-sodium tantalate niobate (K0.5Na0.5(Nb0.95Ta0.05)1-xFexO3-x; x = 0 and 0.01) ceramics prepared by the conventional sintering method were investigated. In comparison with pure ceramics, the 0.01 Fe-doped ceramics show magnetic and ferroelectric properties simultaneously at room temperature. The relative dielectric constant significantly decreases after applying a magnetic field for the Fe-doped ceramics, indicating the coupling between ferroelectric and ferromagnetic orders. Magnetocapacitance of -0.77% was observed at room temperature and 50 kHz by the application of a magnetic field of 5000 Oe.

  18. 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

  19. 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. PMID:25193845

  20. Mechanical, lattice dynamical and electronic properties of CeO2 at high pressure: First-principles studies

    NASA Astrophysics Data System (ADS)

    Li, Mei; Jia, Huiling; Li, Xueyan; Liu, Xuejie

    2016-01-01

    The elastic constants (Cij), bulk modulus (B), shear modulus (G) and elastic modulus (E) of cubic fluorite CeO2 under high pressure have been studied using the plane-wave pseudopotential method based on density functional theory. The calculated results show that the mechanical properties (Cij, B, G and E) of CeO2 increase with increasing pressure, and the phase transition of CeO2 occurs beyond the pressure of 130 GPa. From the calculated phonon spectrum using Parlinsk-Li-Kawasoe method, we found that CeO2 appears imaginary frequency at 140 GPa, which indicates phase transition. The energy band, density of states and charge density of CeO2 under high pressure are calculated using GGA+U method. It is found that the high pressure makes the electron delocalization and Ce-O covalent bonding enhanced. As pressure increases, the band gap between O2p and Ce4f states near the Fermi level increases, and CeO2 nonmetallic nature promotes. The present research results in a better understanding of how CeO2 responds to compression.

  1. 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. PMID:26410773

  2. Effects of the excitation density on the laser output of two differently doped Yb:YAG ceramics.

    PubMed

    Pirri, Angela; Toci, Guido; Alderighi, Daniele; Vannini, Matteo

    2010-08-01

    We report the behavior of two Yb(3+) doped ceramics (i.e. 10% at. and 20% at.) under quasi-continuous wave laser pumping. Two different behaviors are found depending on the density of Yb(3+) in the excited level. Experimental results show that at low population inversion density, the maximum output power and the efficiency are almost independent on the doping concentration. In particular, an output power as high as 8.9 W with a corresponding slope efficiency of 52% with respect to the injected pump power was reached with the 20% at. sample. Conversely, at high population inversion densities, the 20% doped sample shows a sudden decrease of the laser output for increasing pump power, due to the onset of a nonlinear loss mechanism. Finally, we report a comparison of the experimental results with numerical simulations for the evaluation of the inversion density and of the temperature distribution. PMID:20721114

  3. Relaxor in KF-doped BaTi{sub 2}O{sub 5} ceramics by spark plasma sintering

    SciTech Connect

    Xu Jun; Akishige, Yukikuni

    2008-02-04

    Dense BaTi{sub 2}O{sub 5} ceramics with KF doping up to 5 at. % were synthesized by spark plasma sintering (SPS). The SPS method enabled us to overcome the densifying difficulty in conventional sintering which is caused by the limit of the decomposing temperature of this metastable phase. We observed drastic KF-doping effect on the ferroelectric (FE) properties of BaTi{sub 2}O{sub 5}. Although there is only very small change in lattice parameters upon KF doping, the peak temperature in dielectric constant strongly decreases in an exponential way. The diffuseness of phase transition increases and FE relaxor state sets in for KF content as low as 1 at. %. Possible structural reasons for the effect and the implication for the nature of FE phase transition in BaTi{sub 2}O{sub 5} are discussed.

  4. Facile synthesis of Sm3+/Eu3+ codoped CeO2 ultrafine nanocrystals and oxygen vacancy site dependent photoluminescence

    NASA Astrophysics Data System (ADS)

    Vimal, G.; Mani, Kamal P.; Alexander, Dinu; Biju, P. R.; Unnikrishnan, N. V.; Ittyachen, M. A.; Joseph, Cyriac

    2015-12-01

    Ultrafine nanocrystals of Sm3+/Eu3+ codoped CeO2 have been prepared successfully by a simple and facile oxalate decomposition method. The structure, phase and size of the nanocrystals were characterized by X-ray diffraction and transmission electron microscope which confirmed that monodispersed nanocrystals of size below 5 nm are formed by this novel technique. Spectroscopic investigations of the synthesized phosphors are carried out with the help of photoluminescence excitation, emission and decay analysis. The studies revealed that oxygen vacancies introduced in the crystal lattice for charge compensation strongly influences the luminescence properties of the phosphor material. By investigating the luminescence characteristics of the material with different doping concentrations of Sm3+ and Eu3+, the position of the oxygen vacancies with respect to the dopant ion is determined. Also it can be revealed that symmetry of Eu3+ ions are perturbed by the oxygen vacancies at nearest neighbor site which produce strong electric dipole transition emissions in the luminescence spectra. In the case of Sm3+ ions oxygen vacancies are repelled to the next nearest neighbor site and hence the cubic symmetry of the ions is preserved. In addition, occurrence of non radiative energy transfer from Sm3+ to Eu3+ in the phosphor material is confirmed by the close examination of the luminescence spectra. Chromaticity coordinates evidenced that color purity of the synthesized nanophosphors is marginally increased by the proper addition of Sm3+.

  5. 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

  6. 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.

  7. Effect of composition and temperature on electric fatigue of La-doped lead zirconate titanate ceramics

    NASA Astrophysics Data System (ADS)

    Jiang, Q. Y.; Subbarao, E. C.; Cross, L. E.

    1994-06-01

    Composition and temperature of ferroelectric La-doped lead zirconate titanate ceramics influence its electric fatigue behavior, defined as the degradation of the electrical properties under the action of an ac field applied for a long time. Compositions of rhombohedral symmetry exhibit little or no fatigue compared with those of tetragonal and orthorhombic symmetry. At temperatures higher than the dielectric maximum, no fatigue effect was detected. Compositions close to phase boundaries (FE-AFE, FE-FE, or FE-PE) display significant fatigue behavior. Electric fatigue arises from the pinning of domains by space charges or injected carriers or from microcracking. The former (which are charge related) is accompanied by smaller strains and is recoverable by thermal and electrical treatment, while the latter (arising from microcracking) arises from large incompatible stresses between grains and is a permanent damage. The understanding of the mechanism of electric fatigue gained in the present study provides guidelines for enhancing the long-term reliability of devices based on ferroic materials.

  8. Dielectric and Ferroelectric Behavior of Bismuth-Doped Barium Titanate Ceramic Prepared by Microwave Sintering

    NASA Astrophysics Data System (ADS)

    Mahapatra, A.; Parida, S.; Sarangi, S.; Badapanda, T.

    2015-08-01

    Bismuth-doped barium titanate ceramics with the general formula Ba1- x Bi2 x/3TiO3 ( x = 0.0, 0.01, 0.025, 0.05) have been prepared by the solid state reaction technique. The phase formation and structural property of all compositions have been studied by x-ray diffraction (XRD) pattern and Rietveld refinement. XRD pattern reports the single phase tetragonal crystal system with space group of P4mm. All compositions have been sintered at 1100°C in a microwave furnace for 30 min. The variation of dielectric constant with respect to temperature and frequency was studied and it was found that the dielectric constant decreases whereas transition temperature increased with the increase in Bi content. The diffusivity parameter was calculated by the modified Curie-Weiss law and the diffusivity increased with the increase in Bi content. The ferroelectric property was studied by the P-E hysteresis loop and it was observed that the saturation polarization decreased, but the coercive field increased with Bi content. The optical band gap was calculated from UV-Visible spectroscopy and found to decrease with Bi content.

  9. Influence of cation distribution on the magnetic and dielectric properties of Zn doped CFO ceramics

    NASA Astrophysics Data System (ADS)

    Monaji, Vinitha Reddy; Paul Praveen, J.; Raja, Manivel; Das, Dibakar

    2016-05-01

    Cations site registry of Co1-xZnxFe2O4 (0 ≤ x ≤ 0.3) ceramics, synthesized by combustion method, has been estimated using Mossbauer spectroscopic study and Rietveld analysis and its influence on the magnetic and dielectric properties have been studied. Decreased B-site hyperfine field with progressive Zn doping due to the occupancy of non-magnetic Zn ions in the tetrahedral site of CFO lattice has been observed in Mössbauer data. Magnetic moment of Co1-xZnxFe2O4 (0 ≤ x ≤ 0.3) calculated from the cation distribution estimated from the Mössbauer data has been compared with the experimentally observed magnetic moment. Decreased dielectric constants (ɛ') with increasing Zn concentrations, in the frequency range 20Hz - 1MHz (at ~300K), indicates increased Fe+3 concentrations in the octahedral sites. The temperature dependent dielectric data showed a progressive reduction in the magnetic transition temperature (TC) from 528˚C for x = 0 to 422˚C for x = 0.3 of the Co1-xZnxFe2O4 (0 ≤ x ≤ 0.3) samples. Increasing relaxor behavior (γ = 1.85 for x = 0 to γ = 2.2 for x = 0.3) has been observed with increasing Zn content in the CFO lattice.

  10. 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.

  11. AC conductivity and structural properties of Mg-doped ZnO ceramic

    NASA Astrophysics Data System (ADS)

    Othman, Zayani Jaafar; Hafef, Olfa; Matoussi, Adel; Rossi, Francesca; Salviati, Giancarlo

    2015-11-01

    Undoped ZnO and Zn1- x Mg x O ceramic pellets were synthesized by the standard sintering method at the temperature of 1200 °C. The influence of Mg doping on the morphological, structural and electrical properties was studied. The scanning electron microscopy images revealed rough surface textured by grain boundaries and compacted grains having different shapes and sizes. Indeed, the X-ray diffraction reveals the alloying of hexagonal ZnMgO phase and the segregation of cubic MgO phase. The crystallite size, strain and stress were studied using Williamson-Hall (W-H) method. The results of mean particle size of Zn1- x Mg x O composites showed an inter-correlation with W-H analysis and Sherrer method. The electrical conductivity of the films was measured from 173 to 373 K in the frequency range of 0.1 Hz-1 MHz to identify the dominant conductivity mechanism. The DC conductivity is thermally activated by electron traps having activation energy of about 0.09 to 0.8 eV. The mechanisms of AC conductivity are controlled by the correlated barrier hopping model for the ZnO sample and the small polaron tunneling (SPT) model for Zn0.64Mg0.36O and Zn0.60Mg0.40O composites.

  12. 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. PMID:21926151

  13. Enhanced ferromagnetic properties in Ho and Ni co-doped BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    The magnetic properties of polycrystalline Bi1-xHoxFe1-yNiyO3 (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 Bi0.9Ho0.1Fe0.97Ni0.03O3 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, Bi0.9Ho0.1Fe0.97Ni0.03O3 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.

  14. Molecular dynamics simulation of fast particle irradiation on the single crystal CeO2

    NASA Astrophysics Data System (ADS)

    Sasajima, Y.; Ajima, N.; Osada, T.; Ishikawa, N.; Iwase, A.

    2013-11-01

    We used a molecular dynamics method to simulate structural relaxation caused by the high-energy-ion irradiation of single crystal CeO2. As the initial condition, we assumed high thermal energy was supplied to the individual atoms within a cylindrical region of nanometer-order diameter located in the center of the single crystal. The potential proposed by Inaba et al. was utilized to calculate interactions between atoms [H. Inaba, R. Sagawa, H. Hayashi, K. Kawamura, Solid State Ionics 122 (1999) 95-103]. The supplied thermal energy was first spent to change the crystal structure into an amorphous one within a short period of about 0.3 ps, then it was dissipated in the crystal. We compared the obtained results with those of computer simulations for UO2 and found that CeO2 was more stable than UO2 when supplied with high thermal energy.

  15. 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

  16. Sponge phase producing porous CeO2 for catalytic oxidation of CO.

    PubMed

    Song, Shasha; Wang, Haiqiao; Song, Aixin; Dong, Shuli; Hao, Jingcheng

    2014-07-14

    The aggregation behavior of mixtures of the alkaline amino acid L-Arginine (L-Arg) and bis(2-ethylhexyl)phosphoric acid (DEHPA) in water was studied in detail. At a fixed L-Arg concentration, a phase sequence of micellar phase (L1 phase), vesicle phase (Lαv phase), planar lamellar phase (Lαl phase), and sponge phase (L3 phase) was obtained with increasing DEHPA concentration due to changes in the packing parameter. The phase transition of the lamellar structures was determined by freeze-fracture TEM and (2)H NMR spectroscopy. Rheological measurements reflected the phase transition through significant variations of both the elastic modulus and the viscous modulus. Porous CeO2 materials were produced by utilizing the L3 phase as template, and the porous CeO2 exhibited excellent catalytic oxidation activity toward CO due to its high surface area, which provides more active sites for CO conversion. PMID:24895013

  17. 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.

  18. 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.

  19. 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

  20. Role of molting on the biodistribution of CeO2 nanoparticles within Daphnia pulex.

    PubMed

    Auffan, Mélanie; Bertin, Delphine; Chaurand, Perrine; Pailles, Christine; Dominici, Christian; Rose, Jérôme; Bottero, Jean-Yves; Thiery, Alain

    2013-08-01

    As all arthropods, microcrustaceans shed their chitinous exoskeleton (cuticule, peritrophic membrane) to develop and grow. While the molting is the most crucial stage in their life cycle, it remains poorly investigated in term of pollutant biodistribution within the organisms. In this paper, we used optical, electronic, and X ray-based microscopies to study the uptake and release of CeO2 nanoparticles by/from Daphnia pulex over a molting stage. We measured that D. pulex molts every 59 ± 21 h (confidence interval) with growth rates about 1.1 or 1.8 μm per stage as a function of the pieces measured. Ingestion via food chain was the main route of CeO2 nanoparticles uptake by D. pulex. The presence of algae during the exposure to nanoparticles (sub-lethal doses) enhanced by a factor of 3 the dry weight concentration of Ce on the whole D. pulex. Nanoparticles were localized in the gut content, in direct contact with the peritrophic membrane, and on the cuticle. Interestingly, the depuration (24 h with Chlorella pseudomonas) was not efficient to remove the nanoparticles from the organisms. From 40% to 100% (depending on the feeding regime during exposure) of the CeO2 taken up by D. pulex is not release after the depuration process. However, we demonstrated for the first time that the shedding of the chitinous exoskeleton was the crucial mechanism governing the released of CeO2 nanoparticles regardless of the feeding regime during exposure. PMID:23664411

  1. 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.

  2. 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.

  3. 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.

  4. Ceramics

    NASA Astrophysics Data System (ADS)

    Chen, Song; Zhu, De-Gui; Cai, Xu-Sheng

    2014-08-01

    The dense monoclinic-SrAl2Si2O8 ceramics have been prepared by a two-step sintering process at a sintering temperature of 1173 K (900 °C). Firstly, the pre-sintered monoclinic-SrAl2Si2O8 powders containing small SiO2·Al2O3 crystal phases were obtained by continuously sintering a powder mixture of SrCO3 and kaolin at 1223 K (950 °C) for 6 hours and 1673 K (1400 °C) for 4 hours, respectively. Subsequently, by the combination of the pre-sintered ceramic powders with the composite flux agents, which are composed of a SrO·3B2O3 flux agent and α-Al2O3, the low-temperature densification sintering of the monoclinic-SrAl2Si2O8 ceramics was accomplished at 1173 K (900 °C). The low-temperature sintering behavior and microstructure evolvement of the monoclinic-SrAl2Si2O8 ceramics have been investigated in terms of Al2O3 in addition to the composite flux agents. It shows that due to the low-meting characteristics, the SrO·3B2O3 flux agent can urge the dense microstructure formation of the monoclinic-SrAl2Si2O8 ceramics and the re-crystallization of the grains via a liquid-phase sintering. The introduction of α-Al2O3 to the SrO·3B2O3 flux agent can apparently lead to more dense microstructures for the monoclinic-SrAl2Si2O8 ceramics but also cause the re-precipitation of SiO2·Al2O3 compounds because of an excessive Al2O3 content in the SrO·3B2O3 flux agent.

  5. STM and XPS study of CeO2(111) reduction by atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Shahed, Syed Mohammad Fakruddin; Hasegawa, Tomo; Sainoo, Yasuyuki; Watanabe, Yoshihide; Isomura, Noritake; Beniya, Atsushi; Hirata, Hirohito; Komeda, Tadahiro

    2014-10-01

    Reduction of CeO2(111)/Ru(0001) surface by atomic hydrogen was investigated using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). We observed the formation of oxygen vacancy trimers and hydroxyl trimers on the stoichiometric CeO2(111) surface when it was exposed to atomic hydrogen at room temperature. The reaction of an impinging hydrogen atom with a surface oxygen atom yields a hydroxyl species, which diffuse on the surface until stabilized by the formation of OH trimers. The hydrogen atoms were located at atop sites of the oxygen atoms in the topmost surface layer. A reaction between the hopping hydrogen atom and the hydroxyl species yields a water molecule, which is desorbed from the surface leaving an oxygen defect. The oxygen vacancies were also observed as a trimer of vacancies. XPS measurements showed an increase of a reduced Ce and hydroxyl species with an amount of exposed hydrogen atoms. The former was estimated by measuring the ratio of Ce3 +/Ce4 + in the Ce 3d components. Our study shows the formation of hydroxyl trimer species in atomic scale upon atomic hydrogen exposure to CeO2(111) surface which could offer new catalytic activity.

  6. Oxygen vacancy-assisted coupling and enolization of acetaldehyde on CeO2(111).

    PubMed

    Calaza, Florencia C; Xu, Ye; Mullins, David R; Overbury, Steven H

    2012-10-31

    The temperature-dependent adsorption and reaction of acetaldehyde (CH(3)CHO) on a fully oxidized and a highly reduced thin-film CeO(2)(111) surface have been investigated using a combination of reflection-absorption infrared spectroscopy (RAIRS) and periodic density functional theory (DFT+U) calculations. On the fully oxidized surface, acetaldehyde adsorbs weakly through its carbonyl O interacting with a lattice Ce(4+) cation in the η(1)-O configuration. This state desorbs at 210 K without reaction. On the highly reduced surface, new vibrational signatures appear below 220 K. They are identified by RAIRS and DFT as a dimer state formed from the coupling of the carbonyl O and the acyl C of two acetaldehyde molecules. This dimer state remains up to 400 K before decomposing to produce another distinct set of vibrational signatures, which are identified as the enolate form of acetaldehyde (CH(2)CHO¯). Furthermore, the calculated activation barriers for the coupling of acetaldehyde, the decomposition of the dimer state, and the recombinative desorption of enolate and H as acetaldehyde are in good agreement with previously reported TPD results for acetaldehyde adsorbed on reduced CeO(2)(111) [Chen et al. J. Phys. Chem. C 2011, 115, 3385]. The present findings demonstrate that surface oxygen vacancies alter the reactivity of the CeO(2)(111) surface and play a crucial role in stabilizing and activating acetaldehyde for coupling reactions. PMID:23020248

  7. MnO2/CeO2 for catalytic ultrasonic degradation of methyl orange.

    PubMed

    Zhao, He; Zhang, Guangming; Zhang, Quanling

    2014-05-01

    Catalytic ultrasonic degradation of aqueous methyl orange was studied in this paper. Heterogeneous catalyst MnO2/CeO2 was prepared by impregnation of manganese oxide on cerium oxide. Morphology and specific surface area of MnO2/CeO2 catalyst were characterized and its composition was determined. Results showed big differences between fresh and used catalyst. The removal efficiency of methyl orange by MnO2/CeO2 catalytic ultrasonic process was investigated. Results showed that ultrasonic process could remove 3.5% of methyl orange while catalytic ultrasonic process could remove 85% of methyl orange in 10 min. The effects of free radical scavengers were studied to determine the role of hydroxyl free radical in catalytic ultrasonic process. Results showed that methyl orange degradation efficiency declined after adding free radical scavengers, illustrating that hydroxyl free radical played an important role in degrading methyl orange. Theoretic analysis showed that the resonance size of cavitation bubbles was comparable with the size of catalyst particles. Thus, catalyst particles might act as cavitation nucleus and enhance ultrasonic cavitation effects. Measurement of H2O2 concentration in catalytic ultrasonic process confirmed this hypothesis. Effects of pre-adsorption on catalytic ultrasonic process were examined. Pre-adsorption significantly improved methyl orange removal. The potential explanation was that methyl orange molecules adsorbed on catalysts could enter cavitation bubbles and undergo stronger cavitation. PMID:24369902

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

    PubMed Central

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

    2015-01-01

    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. PMID:25835175

  9. 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.

  10. 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.

  11. Fate and effects of CeO2 nanoparticles in aquatic ecotoxicity tests.

    PubMed

    Van Hoecke, Karen; Quik, Joris T K; Mankiewicz-Boczek, Joanna; De Schamphelaere, Karel A C; Elsaesser, Andreas; Van der Meeren, Paul; Barnes, Clifford; McKerr, George; Howard, C Vyvyan; Van de Meent, Dik; Rydzyński, Konrad; Dawson, Kenneth A; Salvati, Anna; Lesniak, Anna; Lynch, Iseult; Silversmit, Geert; De Samber, Björn; Vincze, Laszlo; Janssen, Colin R

    2009-06-15

    Cerium dioxide nanoparticles (CeO2 NPs) are increasingly being used as a catalyst in the automotive industry. Consequently, increasing amounts of CeO2 NPs are expected to enter the environment where their fate in and potential impacts are unknown. In this paper we describe the fate and effects of CeO2 NPs of three different sizes (14, 20, and 29 nm) in aquatic toxicity tests. In each standard test medium (pH 7.4) the CeO2 nanoparticles aggregated (mean aggregate size approximately 400 nm). Four test organisms covering three different trophic levels were investigated, i.e., the unicellular green alga Pseudokirchneriella subcapitata, two crustaceans: Daphnia magna and Thamnocephalus platyurus, and embryos of Danio rerio. No acute toxicity was observed for the two crustaceans and D. rerio embryos, up to test concentrations of 1000, 5000, and 200 mg/L, respectively. In contrast, significant chronic toxicity to P. subcapitata with 10% effect concentrations (EC10s) between 2.6 and 5.4 mg/L was observed. Food shortage resulted in chronic toxicity to D. magna, for wich EC10s of > or = 8.8 and < or = 20.0 mg/L were established. Chronic toxicity was found to increase with decreasing nominal particle diameter and the difference in toxicity could be explained by the difference in surface area. Using the data set, PNEC(aquatic)S > or = 0.052 and < or = 0.108 mg/L were derived. Further experiments were performed to explain the observed toxicity to the most sensitive organism, i.e., P. subcapitata. Toxicity could not be related to a direct effect of dissolved Ce or CeO2 NP uptake or adsorption, nor to an indirect effect of nutrient depletion (by sorption to NPs) or physical light restriction (through shading by the NPs). However, observed clustering of NPs around algal cells may locally cause a direct or indirect effect. PMID:19603674

  12. Raman study of CeO2 texture as a buffer layer in the CeO2/La2Zr2O7/Ni architecture for coated conductors.

    PubMed

    Jiménez, C; Caroff, T; Bartasyte, A; Margueron, S; Abrutis, A; Chaix-Pluchery, O; Weiss, F

    2009-04-01

    The CeO(2)/La(2)Zr(2)O(7)/Ni piled-up structure is a very promising architecture for YBa(2)Cu(3)O(7) (YBCO) coated conductors. We have grown YBCO/CeO(2)/LZO/Ni epitaxial structures by metalorganic decomposition (MOD) and metalorganic chemical vapor deposition (MOCVD) methods. The crystallographic quality of the CeO(2) layer is not well determined by conventional X-ray diffraction (XRD) due to the superposition of LZO and CeO(2) reflections. An alternative simple Raman spectroscopy analysis of the crystalline quality of the CeO(2) films is proposed. The F(2g) Raman mode of CeO(2) can be quantified either by using two polarization configurations (crossed or parallel) or at two different rotation angles around the normal axis (0 degrees and 45 degrees ) to obtain information about the sample texture. The sample texture can be determined via a quality factor (referred to as the Raman intensity ratio, RIR) consisting of calculating the ratio of the integrated intensity of the CeO(2) F(2g) mode at 0 degrees and 45 degrees in parallel polarization. This factor correlates with superconducting performance and the technique can be used as an on-line nondestructive characterization method. PMID:19366505

  13. Selective substitution and tetragonality by Co-doping of dysprosium and thulium on dielectric properties of barium titanate ceramics

    NASA Astrophysics Data System (ADS)

    Kim, Jungdae; Kim, Dowan; Kim, Jinseong; Kim, Yong-Nam; Hui, K. N.; Lee, Heesoo

    2011-06-01

    Barium titanate (BaTiO3) ceramics co-doped with rare-earth elements were investigated in terms of selective substitution and tetragonality. The dielectrics were designed by addition of various Dy2O3 and Tm2O3 contents, for a total of 1 mol. % concentration, and analyzed in a temperature range from -55°C to 150°C. The dielectric constant of the 0.7 mol. % Dy2O3 and the 0.3 mol. % Tm2O3 co-doped BaTiO3 was 2250, which was about 27% higher than those of specimens doped with 1 mol. % Tm2O3 and 1 mol. % Dy2O3 at room temperature. The tendency of dielectric properties was verified through the changes of lattice parameters and binding energy. The substitution of Dy3+ led to a decrease of tetragonality and grain growth; however, amphoteric substitution caused by the co-doping of Dy2O3 and Tm2O3 compensated for those adverse effects. It can be concluded that the improvement of dielectric properties originated from the increase of the site substitution rate of Dy3+ and Tm3+ ions according to the ionic size the in rare-earth doped BaTiO3 system.

  14. 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.

  15. 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.

  16. 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.

  17. Effect of cerium oxide doping on the performance of CaO-based sorbents during calcium looping cycles.

    PubMed

    Wang, Shengping; Fan, Shasha; Fan, Lijing; Zhao, Yujun; Ma, Xinbin

    2015-04-21

    A series of CaO-based sorbents were synthesized through a sol-gel method and doped with different amounts of CeO2. The sorbent with a Ca/Ce molar ratio of 15:1 showed an excellent absorption capacity (0.59 gCO2/g sorbent) and a remarkable cycle durability (up to 18 cycles). The admirable capture performance of CaCe-15 was ascribed to its special morphology formed by the doping of CeO2 and the well-distributed CeO2 particles. The sorbents doped with CeO2 possessed a loose shell-connected cross-linking structure, which was beneficial for the contact between CaO and CO2. CaO and CeO2 were dispersed homogeneously, and the existence of CeO2 also decreased the grain size of CaO. The well-dispersed CeO2, which could act as a barrier, effectively prevented the CaO crystallite from growing and sintering, thus the sorbent exhibited outstanding stability. The doping of CeO2 also improved the carbonation rate of the sorbent, resulting in a high capacity in a short period of time. PMID:25815798

  18. 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.

  19. 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.

  20. Enhanced multiferroic properties in Ti-doped Bi{sub 2}Fe{sub 4}O{sub 9} ceramics

    SciTech Connect

    Tian, Z. M.; Qiu, Y.; Yuan, S. L.; Wu, M. S.; Huo, S. X.; Duan, H. N.

    2010-09-15

    Structural, magnetic, and ferroelectric properties have been investigated for Bi{sub 2}Fe{sub 4(1-x)}Ti{sub 4x}O{sub 9} (0{<=}x{<=}0.2) bulk ceramics, which were synthesized by a modified Pechini method. X-ray diffraction reveals that all samples are single phase with no impurities detected. Compared with antiferromagnetic Bi{sub 2}Fe{sub 4}O{sub 9} compound, doping with Ti ions induces the appearance of weak ferromagnetism at room temperature, which is discussed in terms of the collapse of the frustrated antiferromagnetic spin structure. Moreover, appropriate Ti doping also significantly reduces electric leakage and leads to the enhancement of electrical polarization. Among all samples, the optimal multiferroics with M{sub r{approx}}0.0188 emu/g and P{sub r{approx}}0.262 {mu}C/cm{sup 2} at room temperature is found for x=0.15 ceramics. It is thus shown that Ti-doped Bi{sub 2}Fe{sub 4}O{sub 9} is a promising candidate for preparing multiferroic materials.

  1. Radiation damage studies of cerium-doped radiation-resistant lead glass detectors

    NASA Astrophysics Data System (ADS)

    Adams, M. R.; Engelmann, R.; Grannis, P. D.; Horstkotte, J.; Godfrey, L.; Linn, S. L.; Marx, M. D.; Timms, J.; Tuts, P. M.; Willins, J.; Ahrens, L.; Aronson, S.; Levy, P. W.; Yamin, P.; Franzini, P.; Youssef, S.; Cutts, D.; Callas, J.

    1985-08-01

    Optical absorption measurements have been made on unirradiated and irradiated samples of cerium oxide doped lead silicate particle detector glasses. The addition of CeO 2 introduces one prominent and one weak absorption band near the ultraviolet transmission limit. However the CeO 2 greatly reduces the rate of formation of the radiation induced absorption. Detector size blocks of lead glass with 0.0, 0.25, and 1.2 weight percent CeO 2 were used to determine the energy resolution for 5 GeV electrons. The resolution deteriorates from 12 to 33% as the CeO 2 changes from 0.0 to 1.2%. At these CeO 2 levels, calculations indicate the yield of doped glass becomes superior to that of undoped glass for doses greater than 500 rad.

  2. 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. PMID:18312014

  3. 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.

  4. 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. PMID:25789459

  5. 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.

  6. 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

  7. 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. PMID:26317617

  8. 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

  9. 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

  10. Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Enzhu; Zou, Mengying; Duan, Shuxin; Xu, Ning; Yuan, Ying; Zhou, Xiaohua

    2014-11-01

    The effects of excess Li content on the phase structure and microwave dielectric properties, especially on the temperature coefficient, of LiNb0.6 Ti0.5O3 (LNT) ceramics were studied. The results show that small amounts of Li effectively enhanced the sintering process due to the compensation of high volatility of Li, leading to a densification and homogenous microstructure, and therefore enhanced the dielectric properties. However, too much Li leads to a secondary phase and cause abnormal grain growth. The LNT + 5 wt.% Li ceramic sintered at 1075°C in the air shows the best properties of ɛ r = 69.73, Q × f = 5543 GHz, and τ f = -4.4 ppm/°C.

  11. 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.

  12. [Microstructure and spectral property of Er3+ doped transparent oxyfluoride glass ceramics with high fluorine contents].

    PubMed

    Lin, Le-Jing; Ren, Guo-Zhong; Chen, Min-Peng; Liu, Yang

    2009-12-01

    The microstructure and spectral properties of Er3+ doped transparent oxyfluoride glass ceramics with high fluorine content were reported. Two samples with the same initial contents (50SiO2-45PbF2-5PbO-1ErF3) were prepared under the different preparation parameters. The final fluorine contents were detected by a fluoride ion selective electrode. The results shows that the final fluorine contents increase by covering crucibles with corundum lid during melt. The samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), absorption spectra and upconversion luminescence spectra. The results show that PbF2 crystals were precipitated in the sample with high fluorine content before heat treatment. And the PbF2 crystals precipitated inside the glass matrix are spherical with diameters of approximately 10-15 nm in size from the high resolution TEM micrograph. The absorption spectra, J-O parameters and the upconversion spectra show that the Er3+ ions were located in crystalline and vitreous mixed states. It is different from the sample with low fluorine content which is completely amorphous. After heat treatment, Er3+ ions that remain in the glassy phase entered into fluoride nanocrystals in the sample with high fluorine content. The fluorine environment decreases non-radiative transfer which eases the upconversion processes. Hence, the upconversion luminescence intensity of Er3+ ions in the high fluorine content sample after heat treatment is much stronger than that in the precursor sample. PMID:20210134

  13. 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.

  14. 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.

  15. 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.

  16. Effects of Co doping on electronic structure and electric/magnetic properties of La0.1Bi0.9FeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Wang, ShouYu; Feng, Yu; Liu, WeiFang; Yu, DaShu; Li, DeJun

    2013-10-01

    In this work, we report the influence of Co-doping on the electronic band structure, dielectric and magnetic properties of La0.1Bi0.9Fe1- x Co x O3 ceramics. X-ray photoelectron spectroscopy investigation shows that Co dopant can shift the valence band spectrum and core-level lines of constituent elements towards higher bind energy regions simultaneously increase the concentration of oxygen vacancies in ceramics. The effects of dopant are discussed with focus given to the Co-doping induced enhancement of electrical conductivity and resistive switching phenomena.

  17. 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}.

  18. 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

  19. Interface-engineered resistive switching: CeO(2) nanocubes as high-performance memory cells.

    PubMed

    Younis, Adnan; Chu, Dewei; Mihail, Ionsecu; Li, Sean

    2013-10-01

    We reported a novel and facile approach to fabricate self-assembled CeO2 nanocube-based resistive-switching memory device. The device was found to exhibit excellent bipolar resistive-switching characteristics with a high resistance state (HRS/OFF) to low resistance state (LRS/ON) ratio of 10(4), better uniformity, and stability up to 480 K. The presence of oxygen vacancies and their role was discussed to explain the resistive-switching phenomenon in the fabricated devices. Further, the effect of the film thickness on carrier concentrations and estimated electric field strength with the switching (OFF/ON) ratio were also discussed. PMID:24028707

  20. 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.

  1. Thermo-optical measurements of ytterbium doped ceramics (Sc2O3, Y203, Lu203, YAG) and crystals (YAG, CaF2) at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Le Garrec, B.; Cardinali, V.; Bourdet, G.

    2013-05-01

    In this paper, we report the measurements of the specific heat, the density and the thermal diffusivity at room and cryogenic temperatures of Ytterbium doped cubic sesquioxides (Sc2O3, Y2O3, Lu2O3) ceramics and of Ytterbium doped crystals (YAG, CaF2). These materials appear to have very interesting properties for setting up high average power laser chains useful for plasma physics and for inertial fusion energy drivers.

  2. 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. PMID:27022662

  3. Composition-driven structural phase transitions in rare-earth-doped BiFeO3 ceramics: a review.

    PubMed

    Arnold, Donna C

    2015-01-01

    Bismuth ferrite suffers from high leakage currents and the presence of a complex incommensurate spin cycloidal magnetic ordering, which has limited its commercial viability and has led researchers to investigate the functionality of doped BiFeO3 ceramics. In particular, the substitution of rare earths onto the Bi(3+) site of the perovskite lattice have been shown to lead to improved functional properties, including lower leakage currents and the suppression of the magnetic spin cycloid. There is particular interest in materials with compositions close to structural morphotropic phase boundaries, because these may lead to materials with enhanced electronic and magnetic properties analogous to the highly relevant PbZrO3- PbTiO3 solid solution. However, many contradictory crystal structures and physical behaviors are reported within the literature. To understand the structure-property relationships in these materials, it is vital that we first unravel the complex structural phase diagrams. We report here a comprehensive review of structural phase transitions in rare-earth-doped bismuth ferrite ceramics across the entire lanthanide series. We attempt to rationalize the literature in terms of the perovskite tool kit and propose an updated phase diagram based on an interpretation of the literature. PMID:25585391

  4. Calcium-doping effects on photovoltaic response and structure in multiferroic BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Tu, C. S.; Hung, C.-M.; Xu, Z.-R.; Schmidt, V. H.; Ting, Y.; Chien, R. R.; Peng, Y.-T.; Anthoninappen, J.

    2013-09-01

    Photovoltaic (PV) effects, power-conversion efficiencies, and structures have been systematically measured in (Bi1-xCax)FeO3-δ ceramics for x = 0.05, 0.10, and 0.15. The heterostructures of indium tin oxide (ITO) film/(Bi1-xCax)FeO3-δ ceramics/Au film exhibit significant PV effects under illumination of λ = 405 nm. The maximum power-conversion efficiency in the ITO/(Bi0.90Ca0.10)FeO2.95 (BFO10C)/Au can reach 0.0072%, which is larger than 0.0025% observed in the graphene/polycrystalline BFO/Pt films [Zang et al., Appl. Phys. Lett. 99, 132904 (2011)]. A theoretical model based on optically excited current in the depletion region between ITO film and Ca-doped BFO ceramics is used to describe the I-V characteristic, open-circuit voltage, and short-circuit current density as a function of illumination intensity. This work suggests that the Ca-substitution can reduce the rhombohedral distortion and stabilize the single-phase structure.

  5. 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

  6. 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.

  7. 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.

  8. Simulation and experimental study of rheological properties of CeO2-water nanofluid

    NASA Astrophysics Data System (ADS)

    Loya, Adil; Stair, Jacqueline L.; Ren, Guogang

    2015-10-01

    Metal oxide nanoparticles offer great merits over controlling rheological, thermal, chemical and physical properties of solutions. The effectiveness of a nanoparticle to modify the properties of a fluid depends on its diffusive properties with respect to the fluid. In this study, rheological properties of aqueous fluids (i.e. water) were enhanced with the addition of CeO2 nanoparticles. This study was characterized by the outcomes of simulation and experimental results of nanofluids. The movement of nanoparticles in the fluidic media was simulated by a large-scale molecular thermal dynamic program (i.e. LAMMPS). The COMPASS force field was employed with smoothed particle hydrodynamic potential (SPH) and discrete particle dynamics potential (DPD). However, this study develops the understanding of how the rheological properties are affected due to the addition of nanoparticles in a fluid and the way DPD and SPH can be used for accurately estimating the rheological properties with Brownian effect. The rheological results of the simulation were confirmed by the convergence of the stress autocorrelation function, whereas experimental properties were measured using a rheometer. These rheological values of simulation were obtained and agreed within 5 % of the experimental values; they were identified and treated with a number of iterations and experimental tests. The results of the experiment and simulation show that 10 % CeO2 nanoparticles dispersion in water has a viscosity of 2.0-3.3 mPas.

  9. Ab initio thermodynamic evaluation of Pd atom interaction with CeO(2) surfaces.

    PubMed

    Mayernick, Adam D; Janik, Michael J

    2009-08-28

    Palladium supported on ceria is an effective catalytic material for three-way automotive catalysis, catalytic combustion, and solid-oxide fuel cell (SOFC) anodes. The morphology, oxidation state, and particle size of Pd on ceria affect catalytic activity and are a function of experimental conditions. This work utilizes ab initio thermodynamics using density functional theory (DFT) (DFT+U) methods to evaluate the stability of Pd atoms, PdO(x) species, and small Pd particles in varying configurations on CeO(2) (111), (110), and (100) single crystal surfaces. Over specific oxygen partial pressure and temperature ranges, palladium incorporation to form a mixed surface oxide is thermodynamically favorable versus other single Pd atom states on each ceria surface. For example, Pd atoms may incorporate into Ce fluorite lattice positions in a Pd(4+) oxidation state on the CeO(2) (111) surface. The ceria support shifts the transition between formal Pd oxidation states (Pd(0), Pd(2+), Pd(4+)) relative to bulk palladium and stabilizes certain oxidized palladium species on each surface. We show that temperature, oxygen pressure, and cell potential in a SOFC can influence the stable states of palladium supported on ceria surfaces, providing insight into structural stability during catalytic operation. PMID:19725615

  10. Clustering of Oxygen Vacancies at CeO2(111): Critical Role of Hydroxyls.

    PubMed

    Wu, Xin-Ping; Gong, Xue-Qing

    2016-02-26

    By performing density functional theory calculations corrected by an on site Coulomb interaction, we find that the defects at the CeO_{2}(111) surface observed by the scanning tunneling microscopy (STM) measurements of Esch et al. [Science 309, 752 (2005)] are not mere oxygen vacancies or fluorine impurities as suggested by Kullgren et al. [Phys. Rev. Lett. 112, 156102 (2014)], but actually the hydroxyl-vacancy combined species. Specifically, we show that hydroxyls play a critical role in the formation and propagation of oxygen vacancy clusters (VCs). In the presence of neighboring hydroxyls, the thermodynamically unstable VCs can be significantly stabilized, and the behaviors of oxygen vacancies become largely consistent with the STM observations. In addition to the clarification of the long term controversy on the surface defect structures of CeO_{2}(111), the "hydroxyl-vacancy model" proposed in this work emphasizes the coexistence of hydroxyls and oxygen vacancies, especially VCs, which is important for understanding the catalytic and other physicochemical properties of reducible metal oxides. PMID:26967428

  11. 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

  12. Clustering of Oxygen Vacancies at CeO2(111 ) : Critical Role of Hydroxyls

    NASA Astrophysics Data System (ADS)

    Wu, Xin-Ping; Gong, Xue-Qing

    2016-02-01

    By performing density functional theory calculations corrected by an on site Coulomb interaction, we find that the defects at the CeO2(111 ) surface observed by the scanning tunneling microscopy (STM) measurements of Esch et al. [Science 309, 752 (2005)] are not mere oxygen vacancies or fluorine impurities as suggested by Kullgren et al. [Phys. Rev. Lett. 112, 156102 (2014)], but actually the hydroxyl-vacancy combined species. Specifically, we show that hydroxyls play a critical role in the formation and propagation of oxygen vacancy clusters (VCs). In the presence of neighboring hydroxyls, the thermodynamically unstable VCs can be significantly stabilized, and the behaviors of oxygen vacancies become largely consistent with the STM observations. In addition to the clarification of the long term controversy on the surface defect structures of CeO2(111 ) , the "hydroxyl-vacancy model" proposed in this work emphasizes the coexistence of hydroxyls and oxygen vacancies, especially VCs, which is important for understanding the catalytic and other physicochemical properties of reducible metal oxides.

  13. 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. PMID:26164115

  14. 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. PMID:27220740

  15. 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. PMID:23352517

  16. 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.

  17. 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

  18. Decomposition of 1,2-dichloroethane over CeO2 modified USY zeolite catalysts: effect of acidity and redox property on the catalytic behavior.

    PubMed

    Huang, Qinqin; Xue, Xiaomin; Zhou, Renxian

    2010-11-15

    CeO(2) modified ultrastable Y zeolite (CeO(2)-USY) catalysts were prepared and were used as the catalysts for the decomposition of 1,2-dichloroethane (DCE). The catalytic behavior of these catalysts was evaluated by micro-reaction and temperature-programmed surface reaction (TPSR) technique. The results reveal that CeO(2)-USY catalysts exhibit good catalytic activity for DCE decomposition and high selectivity to the formation of CO(2) and HCl. Both acidity and redox property play important roles in the DCE decomposition, and the synergy between CeO(2) species and USY zeolite shows an enhancement in the catalytic activity for DCE decomposition. CeO(2)-USY (1:8) with high dispersion of CeO(2) species and a much more suitable combination of acidity and redox property exhibits the best catalytic activity. PMID:20709452

  19. 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. PMID:25384333

  20. 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. PMID:26863393

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. Synthesis and characterization of Zn-B-Si-O nano-composites and their doped BaTiO{sub 3} ceramics

    SciTech Connect

    Niu, Ruiyuan; Cui, Bin; Du, Fengtao; Chang, Zhuguo; Tang, Zongxun

    2010-10-15

    We synthesized Zn-B-Si-O (ZBSO) nano-composites via sol-gel process, and then used them to dope BaTiO{sub 3} ceramics. The ZBSO nano-composites and their ceramics were characterized by means of thermogravimetric, Fourier-transform infrared, and X-ray diffraction methods, and using scanning and transmission electron microscopy. We also characterized the dielectric properties of the ceramics. The results indicated that the ZBSO nano-composites were nanometer-scale powders with an amorphous structure. The particle size of the powders increased with increasing pH value, but initially decreased and then increased with increasing calcining temperature. At pH about 2 and with calcining at 400 {sup o}C, the nano-composites attained minimum particle size (about 30 nm). The sintering temperature of the BaTiO{sub 3} ceramics could be reduced to 1100 {sup o}C by adding 5 wt% of the ZBSO nano-composites. Uniform, fine-grained BaTiO{sub 3} ceramics with a high permittivity ({epsilon}{sub r} = 2946 and {epsilon}{sub max} = 5072) were obtained by adding nano-composites; these properties were superior to the ZBSO glass doped BaTiO{sub 3} ceramics.

  6. 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

  7. (001) and (111) Single-Oriented Highly Epitaxial CeO2 Thin Films on r-Cut Sapphire Substrates

    NASA Astrophysics Data System (ADS)

    Bick, D. S.; Sharath, S. U.; Hoffman, I.; Major, M.; Kurian, J.; Alff, L.

    2015-08-01

    We have studied the growth of CeO2 thin films by molecular beam epitaxy on r-cut sapphire substrates. The oxidation state of the substrate surface controls the growth direction of CeO2. Oxygen pre-annealed substrates favor (001) growth, while oxygen vacancies lead to a mixed (001) and (111) orientation. Combining pre- and post-annealing, it is possible to achieve single- oriented CeO2 in both growth directions. Furthermore, post-annealing results in a dramatic increase of crystallinity with a rocking curve width of the (002) reflection as small as 0.004°. We provide a consistent growth model involving oxygen vacancies at the substrate to thin film interface.

  8. 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.

  9. Optical, Structural and Electrochemical Properties of CeO2--Al2O3--SiO2 Thin Films

    NASA Astrophysics Data System (ADS)

    Saygin Hinczewski, Dursen; Hinczewski, Michael; Sorar, Idris; Pehlivan, Esat; Tepehan, Fatma Z.; Tepehan, Galip G.

    2008-03-01

    CeO2 thin films can be used as counter-electrodes in electrochromic devices, but have the disadvantage of slow reaction kinetics. Thus research has shifted to composite CeO2 films as more promising ion-storage candidates. In this work, we examine the sol-gel coating and characterization of CeO2--Al2O3--SiO2 transparent thin films deposited onto glass microslides and indium-tin-oxide-coated conducting glass. We investigate the evolution of the surface morphology, and the optical, structural and electrochemical properties of the films with varying Si-Al-Ce mol ratios. In particular we find the formation of novel complex phase-segregated structures at the surface, which have the potential for enhancing Li ion insertion/extraction.

  10. 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. PMID:24303982

  11. 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.

  12. 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

  13. 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.

  14. Influence of interface point defect on the dielectric properties of Y doped CaCu3Ti4O12 ceramics

    NASA Astrophysics Data System (ADS)

    Deng, Jianming; Sun, Xiaojun; Liu, Saisai; Liu, Laijun; Yan, Tianxiang; Fang, Liang; Elouadi, Brahim

    2016-04-01

    CaCu3Ti4‑xYxO12 (0≤x≤0.12) ceramics were fabricated with conventional solid-state reaction method. Phase structure and microstructure of prepared ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The impedance and modulus tests both suggested the existence of two different relaxation behavior, which were attributed to bulk and grain boundary response. In addition, the conductivity and dielectric permittivity showed a step-like behavior under 405K. Meanwhile, frequency independence of dc conduction became dominant when above 405K. In CCTO ceramic, rare earth element Y3+ ions as an acceptor were used to substitute Ti sites, decreasing the concentration of oxygen vacancy around grain-electrode and grain boundary. The reason to the reduction of dielectric behavior in low frequencies range was associated with the Y doping in CCTO ceramic.

  15. Origin of enhanced multiferroic properties in Dy and Co co-doped BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    Structural, magnetic and ferroelectric properties of polycrystalline BiFeO3, Bi0.9Dy0.1FeO3, BiFe0.97Co0.03O3 and Bi0.9Dy0.1Fe0.97Co0.03O3, which were prepared by solid-state method, have been investigated. The X-ray diffraction (XRD) patterns reveal that all the samples are in single phase and show rhombohedrally distorted perovskite structure with R3c space group. Both XRD and Raman-scattering studies show that Dy and Co co-doped sample has a compressive lattice distortion induced by co-substitution of Dy and Co ions at the A and the B sites, respectively. Dy and Co co-doping favors weak ferromagnetism ordering with evident magnetic hysteresis loop and enhances magnetization values at room temperature. Ferroelectric hysteresis loop for Dy and Co co-doped sample shows the nearly saturated polarization at 40 kV/cm and large remnant polarization. Dy dopant is prominent in the reduced leakage current density, while Co dopant is remarkable in the improved remnant magnetization in Bi0.9Dy0.1Fe0.97Co0.03O3 ceramic. By using a simple model, it was found that the anharmonicity of canted spiral cycloidal spin structure was responsible for the weak ferromagnetism of pure BiFeO3, and the enhanced magnetization in Co-doped sample was attributed to the transition from the incommensurate cycloidal spiral spin structure towards the G-type canted collinear antiferromagnetic structure.

  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. 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.

  18. Facile synthesis of CeO2 nanoplates and nanorods by [100] oriented growth.

    PubMed

    Lin, Hsin-Lung; Wu, Cheng-Yu; Chiang, Ray-Kuang

    2010-01-01

    This study demonstrated a facile method for the synthesis of CeO(2) nanoplates and nanorods via the thermal decomposition of a mixture of cerium acetate, oleic acid, oleyamine and 1-octadecene under controlled atmospheres. Morphologies of the produced cerium oxides were controlled by the adding procedures of activators. Activators added at room temperature and heated with the reaction mixture result in the formation of nanoplates. Injection of activators at high temperature leads to the formation of nanorods. Both the nanoplates and nanorods are achieved via the [100] oriented assembly of smaller particles. A blue-shifting of the UV absorption threshold edge are observed for the cerium oxide nanoplates and nanorods, contrasting with the bulk commercial powders. PMID:19833346

  19. 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.

  20. 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. PMID:19435083

  1. On the properties of aluminium doped zinc oxide thin films deposited on plastic substrates from ceramic targets

    NASA Astrophysics Data System (ADS)

    Girtan, M.; Vlad, A.; Mallet, R.; Bodea, M. A.; Pedarnig, J. D.; Stanculescu, A.; Mardare, D.; Leontie, L.; Antohe, S.

    2013-06-01

    We report on the deposition of Al doped ZnO (AZO) thin films on unheated polyethylene terephthalate (PET) substrates by pulsed laser deposition technique using a UV excimer laser and Al2O3:ZnO ceramic targets (1.5 and 2 wt% Al2O3). The deposited AZO films have been investigated by atomic force microscopy, scanning electron microscopy, X-ray diffraction, and optical spectrophotometry. Films present excellent optical and electrical properties (transmission in the visible range T > 85%; resistivity at room temperature ρ = 1.3 × 10-3 Ω cm) as electrodes for plastic solar cells. A good correlation was found between deposition conditions (laser fluence) and structural, morphological, optical and electrical properties.

  2. 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.

  3. 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.

  4. Enhanced ferromagnetism in co-doped BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Trivedi, Harsh; Singh, Deepa; Gupta, Rajeev; Garg, Ashish

    2012-02-01

    BiFeO3 (BFO) is the most studied multiferroic material with high ferroelectric polarization as well above room temperature transition temperatures. Studies have shown significant improvements in the electrical and magnetic properties of BFO upon atomic substitutions at Bi (A) and Fe (B) sites. While enhanced ferromagnetism upon A-site doping is attributed to the suppression of cycloidal spin ordering of Fe moments, B site substitution reduces leakage current by eliminating oxygen vacancies. This study aims to combine these two aspects by co-doping the material at A- and B- sites using La^3+ and V^3+/V^+5 respectively and to investigate the electrical and magnetic characteristics of co-doped BFO. La-doped LaxBi1-xFeO3 and co-doped LaxBi1-xVyFe1-yO3 (x = .05, 0.1, 0.15, 0.2; y = 0.03) samples were prepared solid-state reaction method. While La-doped samples show only reduced leakage without any discernible change in the magnetic characteristics, co-doped samples (La^3+ & V^5+ ) show significant enhancements in magnetic properties in addition to reduced leakage attributed to the elimination of oxygen vacancies. Improvement in the magnetic characteristics can be understood as a consequence of enhanced double exchange interaction between adjacent Fe ions. This argument is further strengthened by our observation that co-doped samples made by substitution of Fe with V^+3 show a magnetic response equivalent to that of only La-doped BFO samples.

  5. Structural Transition and Enhanced Ferromagnetic Properties of La, Nd, Gd, and Dy-Doped BiFeO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Kumar, Ashwini; Varshney, Dinesh

    2015-11-01

    The structural, electrical, and magnetic properties of rare-earth-doped Bi0.8 RE0.2FeO3 ceramics (rare-earth (RE) = La, Nd, Gd, and Dy) synthesized by solid-state reaction are reported and discussed. The x-ray diffraction (XRD) patterns of Bi0.8La0.2FeO3 and Bi0.8Nd0.2FeO3 were indexed to rhombohedral ( R3 c) and triclinic ( P1) structures, respectively. Rietveld refinement of the XRD pattern of Bi0.8Dy0.2FeO3 confirmed its biphasic nature ( Pnma + R3 c space groups) whereas for Bi0.8Gd0.2FeO3 the orthorhombic phase with Pna21 symmetry made a major contribution, with minor contributions from the orthorhombic ( Pnma) and rhombohedral ( R3 c) phases. Raman spectroscopy revealed changes in BiFeO3 mode positions, in addition to structural changes, on RE ion substitution. The effect of RE ion substitution on dielectric constant and loss tangent were studied at room temperature in a wide range of frequency, 50 Hz-1 MHz. Room temperature magnetization-magnetic field ( M- H) measurements indicated that magnetization increased with increasing structural distortion and with partial destruction of the spin cycloid as a result of doping of BiFeO3 ceramics with rare earth ions. These compounds, with improved remnant magnetization and coercive field, are suitable for use in spin-based electronic devices.

  6. Performance of Europium-Doped Strontium Iodide, Transparent Ceramics and Bismuth-loaded Polymer Scintillators

    SciTech Connect

    Cherepy, Nerine; Payne, Stephen A.; Sturm, Benjamin; O’Neal, S P; Seeley, Zachary; Drury, Owen; Haselhorst, L K; Rupert, B. L.; Sanner, Robert; Thelin, P; Fisher, S E; Hawrami, Rastgo; Shah, Kanai; Burger, Arnold; Ramey, Joanne Oxendine; Boatner, Lynn A

    2011-01-01

    Recently discovered scintillators for gamma ray spectroscopy, single crystal SrI2(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 SrI2(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 ~75,000 Ph/MeV, high stopping, and low radiation damage. Implementation of single crystal SrI2(Eu), Gd-based transparent ceramics, and Bi-loaded plastic scintillators can advance the state-of-the art in ionizing radiation detection systems.

  7. 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.

  8. 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).

  9. Performance of europium-doped strontium iodide, transparent ceramics and bismuth-loaded polymer scintillators

    NASA Astrophysics Data System (ADS)

    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.

    2011-09-01

    Recently discovered scintillators for gamma ray spectroscopy - single-crystal SrI2(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 SrI2(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 SrI2(Eu), Gd-based transparent ceramics, and Bi-loaded plastic scintillators can advance the state-of-the art in ionizing radiation detection systems.

  10. Demonstration of a Yb3+-doped Lu3Al5O12 ceramic thin-disk laser.

    PubMed

    Nakao, Hiroaki; Shirakawa, Akira; Ueda, Ken-ichi; Yagi, Hideki; Yanagitani, Takagimi; Weichelt, Birgit; Wentsch, Katrin; Ahmed, Marwan Abdou; Graf, Thomas

    2014-05-15

    Yb:LuAG ceramic is very promising for thin-disk laser and amplifier architectures since it exhibits a higher thermal conductivity at high doping concentrations and a larger emission cross section than Yb:YAG. In this Letter, we present what we believe to be the first demonstration of a thin-disk laser based on Yb:LuAG ceramic. A maximum output power of 101 W with an optical efficiency of 56% and a slope efficiency of 64% was obtained with a multimode laser resonator. Fundamental-mode laser operation with near diffraction limited beam quality (M2≈1.22) was also achieved. The fundamental-mode laser resonator showed the output power of 49 W, an optical efficiency of 31%, and a slope efficiency of 44%. A linearly polarized output beam was demonstrated in multimode operation using an intracavity Brewster window. The depolarization loss was measured to be as low as 0.15% per round trip. PMID:24978228

  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. Nanostructures of Sr2+ doped BiFeO3 multifunctional ceramics with tunable photoluminescence and magnetic properties.

    PubMed

    Mandal, S K; Rakshit, T; Ray, S K; Mishra, S K; Krishna, P S R; Chandra, Amreesh

    2013-02-01

    Careful tuning of formation (calcination) temperature of Sr(2+) doped BiFeO(3) multiferroic ceramics results in tailorable particle morphologies ranging from spherical to pillar-like. Based on the minimization of Gibb's free energy approach, the dominant homogeneous mechanism for particle growth is suggested. The chemical substitution of a trivalent ion (Bi(3+)) by a divalent ion (Sr(2+)) causes the transformation of certain fraction of Fe(3+) to Fe(4+) and/or the appearance of oxygen vacancies. This has been respectively proved by the analysis of XPS and refinement of neutron diffraction data. Although significant modification in the particle morphology is observed, the crystal unit cell remains rhombohedral with a R3c space group but interesting variations in physical properties are achieved. O-vacancies induced strong and sharp photoluminescence activity in the IR region, similar to ZnO, is reported for the first time. This observation opens up a new application for multiferroic ceramics. SQUID M-H data confirms the straightening of the canted spin structure of BiFeO(3), which in turn results in magnetism similar to ferromagnetic materials. Findings of the magneto-dielectric effect are also discussed to claim the multiferroic nature of the sample. PMID:23300169

  13. Nanostructures of Sr2+ doped BiFeO3 multifunctional ceramics with tunable photoluminescence and magnetic properties

    NASA Astrophysics Data System (ADS)

    Mandal, S. K.; Rakshit, T.; Ray, S. K.; Mishra, S. K.; Krishna, P. S. R.; Chandra, Amreesh

    2013-02-01

    Careful tuning of formation (calcination) temperature of Sr2+ doped BiFeO3 multiferroic ceramics results in tailorable particle morphologies ranging from spherical to pillar-like. Based on the minimization of Gibb’s free energy approach, the dominant homogeneous mechanism for particle growth is suggested. The chemical substitution of a trivalent ion (Bi3+) by a divalent ion (Sr2+) causes the transformation of certain fraction of Fe3+ to Fe4+ and/or the appearance of oxygen vacancies. This has been respectively proved by the analysis of XPS and refinement of neutron diffraction data. Although significant modification in the particle morphology is observed, the crystal unit cell remains rhombohedral with a R3c space group but interesting variations in physical properties are achieved. O-vacancies induced strong and sharp photoluminescence activity in the IR region, similar to ZnO, is reported for the first time. This observation opens up a new application for multiferroic ceramics. SQUID M-H data confirms the straightening of the canted spin structure of BiFeO3, which in turn results in magnetism similar to ferromagnetic materials. Findings of the magneto-dielectric effect are also discussed to claim the multiferroic nature of the sample.

  14. 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

  15. 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)

  16. 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.

  17. Enhanced photocatalytic activity of CeO2 using β-cyclodextrin on visible light assisted decoloration of methylene blue.

    PubMed

    Pitchaimuthu, Sakthivel; Velusamy, Ponnusamy

    2014-01-01

    An attempt has been made to enhance the photocatalytic activity of CeO(2) for visible light assisted decoloration of methylene blue (MB) dye in aqueous solutions by β-cyclodextrin (β-CD). The inclusion complexation patterns between host and guest (i.e., β-CD and MB) have been confirmed with UV-visible spectral data. The interaction between CeO(2) and β-CD has also been characterized by field emission scanning electron microscopy analysis. The photocatalytic activity of the catalyst under visible light was investigated by measuring the photodegradation of MB in aqueous solution. The effects of key operational parameters such as initial dye concentration, initial pH, CeO(2) concentration as well as illumination time on the decolorization extents were investigated. Among the processing parameters, the pH of the reaction solution played an important role in tuning the photocatalytic activity of CeO(2). The maximum photodecoloration rate was achieved at basic pH (pH 11). Under the optimum operational conditions, approximately 99.6% dye removal was achieved within 120 min. The observed results indicate that the decolorization of the MB followed a pseudo-first order kinetics. PMID:24434976

  18. 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

  19. Cyclotron production of radioactive CeO(2) nanoparticles and their application for in vitro uptake studies.

    PubMed

    Simonelli, Federica; Marmorato, P; Abbas, K; Ponti, J; Kozempel, J; Holzwarth, U; Franchini, F; Rossi, F

    2011-03-01

    Nowadays, a wide variety of nanoparticles (NPs) are applied in different fields such as medical science and industry. Due to their large commercial volume, the OECD Working Party on Manufactured Nanomaterials (NMs) has proposed to study a set of 14 nanomaterials, one of which being cerium oxide (CeO(2)). In particular, CeO(2) based NPs are widely used in automotive industry, healthcare, and cosmetics. In this paper, we propose a method for the production of radioactive CeO(2) NPs.We demonstrate that they maintain the same physicochemical characteristics as the “cold” ones in terms of size distribution and Zeta potential; we develop a new protocol to assess their cellular interaction in immortalized mouse fibroblast cell line Balb/3T3, a model for the study of basal cytotoxicity and carcinogenic potential induced by chemicals and in the present case by NPs. Experimental result of this work, which shows a quasi-linear concentration-uptake response of cells, can be useful as a reference dose-uptake curve for explaining effects following biological uptake after exposure to CeO(2) NPs. PMID:21518669

  20. 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. PMID:26878202

  1. Optical and electrochemical properties of sol-gel spin-coated CeO2-TiO2 films

    NASA Astrophysics Data System (ADS)

    Ozer, Nilgun; De Souza, Selmar; Lampert, Carl M.

    1995-08-01

    The optical and electrochemical properties of sol-gel spin coated CeO2-TiO2 (50% CeO2) films were investigated for electrochromic applications. The coating solutions were prepared by using mixed organic-inorganic [Ti(OC2H5)4 and Ce(NH4)2 (NO3)6] precursors. X-ray diffraction studies showed the sol-gel spin- coated films were composed of an amorphous matrix of titanium oxide containing nanocrystallites of cerium oxide. The coating solar transmission value was Ts equals 0.8 (250 nm thick). The refractive index and the extinction coefficient were derived from transmittance measurements in the UV-VIS-NIR regions. These films had refractive index value of n equals 2.18 and extinction coefficient value of k equals 8 X 10-4 at (lambda) equals 550 nm. Cyclic voltametric measurements showed reversible electrochemical insertion of lithium ions in a CeO2-TiO2/LiClO4-propylene carbonate electrochemical cell. During cycling the films maintain high optical transmittance. Spectrophotometric and electrochemical investigations performed on CeO2-TiO2 films revealed that these films are suitable as an optically passive counter-electrode in lithium electrochromic devices.

  2. 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.

  3. 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

  4. 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...

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. 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. PMID:26377118

  15. Spectroscopic characteristics of Dy3+ doped Y3Al5O12 transparent ceramics

    NASA Astrophysics Data System (ADS)

    Lupei, A.; Lupei, V.; Gheorghe, C.; Ikesue, A.; Enculescu, M.

    2011-10-01

    The spectroscopic characteristics of Dy3+ in YAG (Y3Al5O12) transparent ceramics prepared by solid state synthesis were investigated, with special attention to the visible (yellow, blue) emissions that could be pumped directly by the new developed blue-violet or near UV laser diodes. The absorption and emission spectra, recorded at different temperatures from 10 to 300 K, were analyzed and relevant new parameters, improved energy level scheme, temperature effects, intensity parameters based on Judd-Ofelt theory and radiative transition rates, branching ratios, etc., were estimated and the data are compared with previous reports on garnet single crystals. The potential of the Dy3+: YAG transparent ceramics for yellow or blue laser emission is discussed.

  16. Synthesis and optical properties of Pr and Ti doped BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Singh, Vikash; Sharma, Subhash; Dwivedi, R. K.

    2016-05-01

    Bi1-xPrxFe1-xTixO3 ceramics with x = 0.00, 0.10 and 0.20 were synthesized by solid state reaction method. Rietveld fitting of diffraction data reveals structural transition from rhombohedral phase (R3C) for x ≤ 0.10 to orthorhombic phase (Pnma) for x = 0.20. FTIR spectra exhibit broad absorption bands, which may be due to the overlapping of Fe-O and Bi-O vibrations in these ceramics. UV-visible spectroscopy results show strong absorption of light in the spectral range of 400-600 nm, indicating optical band gap in the visible region for these samples.

  17. Piezoelectric/photoluminescence effects in rare-earth doped lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Yao, Qirong; Wang, Feifei; Jin, Chengchao; Tang, Yanxue; Wang, Tao; Shi, Wangzhou

    2013-10-01

    In the present work, we report the environmentally-friendly multifunctional effects—piezoelectric/photoluminescence effects, which originated from the combination of the electromechanical properties and the photoluminescence effect through introducing the rare-earth elements (Pr and Eu) into the (Bi0.5Na0.5)TiO3-BaTiO3 ceramics with the composition around the morphotropic phase boundary. Compared to the pure piezoelectric ceramic, the proposed system simultaneously exhibited enhanced ferroelectric, piezoelectric, dielectric properties along with strong photoluminescence effects, which exhibited potential applications in sensor, and electro-mechano-optical integration. In addition, the present work also provides a promising path for us to fabricate multifunctional composites.

  18. Precipitation of ZnO in Al 2O 3-doped zinc borate glass ceramics

    NASA Astrophysics Data System (ADS)

    Masai, Hirokazu; Ueno, Takahiro; Takahashi, Yoshihiro; Fujiwara, Takumi

    2011-10-01

    Crystallization behavior of the oxide semiconductor ZnO in zinc borate glass was investigated. The precipitated crystalline phase of glass ceramics containing a small amount of Al 2O 3 was α-Zn 3B 2O 6 whereas that of the glass ceramics containing a large amount of Al 2O 3 was ZnO. It was found that the c-oriented precipitation of ZnO in a glass ceramic was brought about by the in-plane crystal growth of needle-like ZnO crystallites along the a-axis. Amount of Al 2O 3 that can make glass network affected the coordination state of B 2O 3 in the glass, and a three-coordinated BO 3 unit was preferentially formed in the glass containing a higher amount of Al 2O 3. The present results suggest that crystallization of ZnO from multi-component glass is dominated by the local coordination state of the mother glass.

  19. Optoenergy storage, stimulated processes in optical amplification with electro-optic ceramic gain media of Nd3+ doped lanthanum lead zirconate titanate

    NASA Astrophysics Data System (ADS)

    Wu, Ye; Zhao, Hua; Zou, Yingyin K.; Chen, Xuesheng; Bartolo, Baldassare Di; Zhang, Jingwen W.

    2011-08-01

    Optical amplification was observed in electro-optic (EO) ceramic plates of neodymium doped lanthanum-modified lead zirconate titanate (Nd3+:PLZT), when the pumping and seeding beams are not overlapped temporarily. This striking feature in the gain measurement and the accompanying slowly trailing-off both seen in the optical amplification as well as in the lasing action are satisfactorily explained by electron releasing from the rich vacancy-based carrier traps in the intrinsically disordered ceramics, i.e., the consecutively optical, thermal stimuli are found responsible for the long persistent optoenergy storage, and consequently the slow response of the gain dynamics. These findings in optical amplification, the slowly trailing-off, and the underlying mechanism have opened a new way of developing novel controllable optical devices. The model thus established could serve as a guide in design and refinement of a new generation of products out of this excellent, well commercialized EO PLZT ceramics family and similar others.

  20. 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

  1. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Jinglei; Li, Fei; Li, Chao; Yang, Guang; Xu, Zhuo; Zhang, Shujun

    2015-02-01

    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.

  2. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics.

    PubMed

    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

  3. Fabrication and characterization of Er+3 doped SiO2/SnO2 glass-ceramic thin films for planar waveguide applications

    NASA Astrophysics Data System (ADS)

    Guddala, S.; Chiappini, A.; Armellini, C.; Turell, S.; Righini, G. C.; Ferrari, M.; Narayana Rao, D.

    2015-02-01

    Glass-ceramics are a kind of two-phase materials constituted by nanocrystals embedded in a glass matrix and the respective volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramics. Among these properties transparency is crucial in particular when confined structures, such as, dielectric optical waveguides, are considered. Moreover, the segregation of dopant rare-earth ions, like erbium, in low phonon energy crystalline medium makes these structures more promising in the development of waveguide amplifiers. Here we are proposing a new class of low phonon energy tin oxide semiconductor medium doped silicate based planar waveguides. Er3+ doped (100-x) SiO2-xSnO2 (x= 10, 20, 25 and 30mol%), glass-ceramic planar waveguide thin films were fabricated by a simple sol-gel processing and dip coating technique. XRD and HRTEM studies indicates the glass-ceramic phase of the film and the dispersion of ~4nm diameter of tin oxide nanocrystals in the amorphous phase of silica. The spectroscopic assessment indicates the distribution of the dopant erbium ions in the crystalline medium of tin oxide. The observed low losses, 0.5±0.2 dB/cm, at 1.54 μm communication wavelength makes them a quite promising material for the development of high gain integrated optical amplifiers.

  4. 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. PMID:26851092

  5. Stability and Temperature-Induced Agglomeration of Rh Nanoparticles Supported by CeO2.

    PubMed

    Varga, Erika; Pusztai, Péter; Oszkó, Albert; Baán, Kornélia; Erdőhelyi, András; Kónya, Zoltán; Kiss, János

    2016-03-22

    The effects of reduction by H2 and by heat treatment in vacuum and in O2 flow on Rh particle size changes of Rh/CeO2 samples were studied by X-ray photoelectron spectroscopy (XPS), high-resolution electron microscopy (HRTEM), and CO adsorption followed by diffuse reflectance infrared spectroscopy (DRIFTS). Low-temperature (373-423 K) reduction of Rh without agglomeration is demonstrated. An average particle size of 2.3 ± 1.1 nm was measured by HRTEM regardless of the metal loading (1-5%). On Rh/CeO2, a significant particle size increase of the Rh particles was detected on heating (773 K). In this work, we suggest that the temperature-induced surface decrease resulting from the sintering of Rh is favored only for well-dispersed particles. XP spectra revealed that the mobile oxygens of CeO2 fundamentally determine the oxidation state of the supported metals. At elevated temperature, the oxidation of the reduced support surface as well as the metal component takes place because of the segregation of ceria oxygens. When the aggregated particles were reoxidized, the redispersion of Rh was observed probably because of the formation of Rh-O-Ce bonds. PMID:26914641

  6. 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

  7. 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.

  8. 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. PMID:27341245

  9. 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

  10. A 1,2-propylene oxide sensor utilizing cataluminescence on CeO2 nanoparticles.

    PubMed

    Liu, Hongmei; Zhang, Yantu; Zhen, Yanzhong; Ma, Yuan; Zuo, Weiwei

    2014-12-01

    A simple and sensitive gas sensor was proposed for the determination of 1,2-propylene oxide (PO) based on its cataluminescence (CTL) by oxidation in the air on the surface of CeO2 nanoparticles. The luminescence characteristics and optimal conditions were investigated in detail. Under optimized conditions, the linear range of the CTL intensity versus the concentration of PO was 10-150 ppm, with a correlation coefficient (r) of 0.9974 and a limit of detection (S/N = 3) of 0.9 ppm. The relative standard deviation for 40 ppm PO was 1.2% (n = 7). There was no or only weak response to common foreign substances including acetone, formaldehyde, ethyl acetate, acetic acid, chloroform, propanol, carbon tetrachloride, ether and methanol. There was no significant change in the catalytic activity of the sensor for 100 h. The proposed method was simple and sensitive, with a potential of detecting PO in the environment and industry. PMID:24802092

  11. 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

  12. Room temperature dielectric and magnetic properties of Gd and Ti co-doped BiFeO{sub 3} ceramics

    SciTech Connect

    Basith, M. A. E-mail: arima@yz.yamagata-u.ac.jp; Kurni, O.; Alam, M. S.; Sinha, B. L.; Ahmmad, Bashir E-mail: arima@yz.yamagata-u.ac.jp

    2014-01-14

    Room temperature dielectric and magnetic properties of BiFeO{sub 3} samples, co-doped with magnetic Gd and non-magnetic Ti in place of Bi and Fe, respectively, were reported. The nominal compositions of Bi{sub 0.9}Gd{sub 0.1}Fe{sub 1–x}Ti{sub x}O{sub 3} (x = 0.00-0.25) ceramics were synthesized by conventional solid state reaction technique. X-ray diffraction patterns revealed that the substitution of Fe by Ti induces a phase transition from rhombohedral to orthorhombic at x > 0.20. Morphological studies demonstrated that the average grain size was reduced from ∼1.5 μm to ∼200 nm with the increase in Ti content. Due to Ti substitution, the dielectric constant was stable over a wide range of high frequencies (30 kHz to 20 MHz) by suppressing the dispersion at low frequencies. The dielectric properties of the compounds are associated with their improved morphologies and reduced leakage current densities probably due to the lower concentration of oxygen vacancies in the compositions. Magnetic properties of Bi{sub 0.9}Gd{sub 0.1}Fe{sub 1–x}Ti{sub x}O{sub 3} (x = 0.00-0.25) ceramics measured at room temperature were enhanced with Ti substitution up to 20% compared to that of pure BiFeO{sub 3} and Ti undoped Bi{sub 0.9}Gd{sub 0.1}FeO{sub 3} samples. The enhanced magnetic properties might be attributed to the substitution induced suppression of spiral spin structure of BiFeO{sub 3}. An asymmetric shifts both in the field and magnetization axes of magnetization versus magnetic field curves was observed. This indicates the presence of exchange bias effect in these compounds notably at room temperature.

  13. Room temperature dielectric and magnetic properties of Gd and Ti co-doped BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Basith, M. A.; Kurni, O.; Alam, M. S.; Sinha, B. L.; Ahmmad, Bashir

    2014-01-01

    Room temperature dielectric and magnetic properties of BiFeO3 samples, co-doped with magnetic Gd and non-magnetic Ti in place of Bi and Fe, respectively, were reported. The nominal compositions of Bi0.9Gd0.1Fe1-xTixO3 (x = 0.00-0.25) ceramics were synthesized by conventional solid state reaction technique. X-ray diffraction patterns revealed that the substitution of Fe by Ti induces a phase transition from rhombohedral to orthorhombic at x > 0.20. Morphological studies demonstrated that the average grain size was reduced from ˜1.5 μm to ˜200 nm with the increase in Ti content. Due to Ti substitution, the dielectric constant was stable over a wide range of high frequencies (30 kHz to 20 MHz) by suppressing the dispersion at low frequencies. The dielectric properties of the compounds are associated with their improved morphologies and reduced leakage current densities probably due to the lower concentration of oxygen vacancies in the compositions. Magnetic properties of Bi0.9Gd0.1Fe1-xTixO3 (x = 0.00-0.25) ceramics measured at room temperature were enhanced with Ti substitution up to 20% compared to that of pure BiFeO3 and Ti undoped Bi0.9Gd0.1FeO3 samples. The enhanced magnetic properties might be attributed to the substitution induced suppression of spiral spin structure of BiFeO3. An asymmetric shifts both in the field and magnetization axes of magnetization versus magnetic field curves was observed. This indicates the presence of exchange bias effect in these compounds notably at room temperature.

  14. Sucrose-assisted synthesis of three-dimensionally ordered macroporous CeO2 and its use as a support for promotional catalytic performance of CO oxidation

    NASA Astrophysics Data System (ADS)

    Liu, Zhi; Tan, Xiuli; Lv, Cong

    2013-10-01

    In this work, several three-dimensionally ordered macroporous (3DOM) CeO2 having hierarchical pore structure were successfully prepared via a dual ‘hard-soft’ templating strategy using Ce(NO3)3·6H2O containing sucrose as the ceria precursor. The resulting CeO2 samples were characterized by N2 adsorption-desorption analysis, scanning electron microscopy, and transmission electron microscopy, which showed that the hierarchical 3DOM CeO2 possessed interconnected networks of the ordered macropore structures with large mesopores, and both the BET surface area and pore volume increased significantly compared with the conventional 3DOM CeO2. The content of sucrose had a great effect on the textural parameters of the 3DOM CeO2. The improved textural parameters should be attributed to the emergence of mesopores in the interconnected three-dimensional skeleton, which were formed by oxidative removal of carbon produced from carbonization of sucrose. The hierarchical 3DOM CeO2 exhibited a superior performance to the conventional 3DOM or bulk CeO2 when used as supports for Ir catalysts in CO oxidation.

  15. Renewable H2 from glycerol steam reforming: effect of La2O3 and CeO2 addition to Pt/Al2O3 catalysts.

    PubMed

    Montini, Tiziano; Singh, Rakesh; Das, Piyali; Lorenzut, Barbara; Bertero, Nicolás; Riello, Pietro; Benedetti, Alvise; Giambastiani, Giuliano; Bianchini, Claudio; Zinoviev, Sergey; Miertus, Stanislav; Fornasiero, Paolo

    2010-05-25

    Glycerol is the main byproduct of biodiesel production and its increased production volume derives from the increasing demand for biofuels. The conversion of glycerol to hydrogen-rich mixtures presents an attractive route towards sustainable biodiesel production. Here we explored the use of Pt/Al(2)O(3)-based catalysts for the catalytic steam reforming of glycerol, evidencing the influence of La(2)O(3) and CeO(2) doping on the catalyst activity and selectivity. The addition of the latter metal oxides to a Pt/Al(2)O(3) catalyst is found to significantly improve the glycerol steam reforming, with high H(2) and CO(2) selectivities. A good catalytic stability is achieved for the Pt/La(2)O(3)/Al(2)O(3) system working at 350 degrees C, while the Pt/CeO(2)/Al(2)O(3) catalyst sharply deactivates after 20 h under similar conditions. Studies carried out on fresh and exhausted catalysts reveal that both systems maintain high surface areas and high Pt dispersions. Therefore, the observed catalyst deactivation can be attributed to coke deposition on the active sites throughout the catalytic process and only marginally to Pt nanoparticle sintering. This work suggests that an appropriate support composition is mandatory for preparing high-performance Pt-based catalysts for the sustainable conversion of glycerol into syngas. PMID:20422673

  16. Enhanced dielectric response of GeO{sub 2}-doped CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

    SciTech Connect

    Amaral, F.; Rubinger, C. P. L.; Valente, M. A.; Costa, L. C.; Moreira, R. L.

    2009-02-01

    CaCu{sub 3}Ti{sub 4}O{sub 12} ceramic samples were prepared by solid state conventional route using stoichiometric amounts of CuO, TiO{sub 2}, and CaCO{sub 3}. Afterward the material was doped with GeO{sub 2} with concentrations up to 6% by weight and sintered at 1050 deg. C for 12 h. The influence of doping on the microstructure, vibrational modes, and dielectric properties of the material was investigated by x-ray diffraction, scanning electron microscopy coupled with an energy dispersive spectrometer, and infrared and dielectric measurements between 100 Hz and 30 MHz. The materials presented huge dielectric response, which increases with doping level relative to undoped CaCu{sub 3}Ti{sub 4}O{sub 12}. The main effect of doping on the microstructure is the segregation of Cu-rich phase in the ceramic grain boundaries. Cole-Cole modeling correlates well the effects of this segregation with the relaxation parameters obtained. The intrinsic phonon contributions for the dielectric response were obtained and discussed together with the structural evolution of the system.

  17. 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

  18. 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

  19. Study of the growth of biaxially textured CeO2 films during ion-beam-assisted deposition

    NASA Astrophysics Data System (ADS)

    Kim, Chang Su; Jo, Sung Jin; Jeong, Soon Moon; Kim, Woo Jin; Baik, Hong Koo; Lee, Se Jong; Song, Kie Moon

    2005-03-01

    Biaxially textured CeO2 films were deposited on Hastelloy C276 substrates at room temperature using ion-beam-assisted e-beam evaporation with the ion beam directed at 55° to the normal of the film plane. The crystalline structure and in-plane orientation of films were investigated by x-ray diffraction 2θ-scan and phgr-scan. The orientation of the films was studied as a function of ion-to-atom ratio and film thickness. The ion-to-atom ratio was varied by independently adjusting the deposition rate and the ion current density. Under optimum condition, (200) textured CeO2 films have been successfully grown on Hastelloy C276.

  20. 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.

  1. A perfectly stoichiometric and flat CeO2(111) surface on a bulk-like ceria film

    NASA Astrophysics Data System (ADS)

    Barth, C.; Laffon, C.; Olbrich, R.; Ranguis, A.; Parent, Ph.; Reichling, M.

    2016-02-01

    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.

  2. 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.

  3. Effect of Microstructure on the Radioluminescence and Transparency of Ce-Doped Strontium Hafnate Ceramics

    PubMed Central

    van Loef, Edgar V.; Wang, Yimin; Miller, Stuart R.; Brecher, Charles; Rhodes, William H.; Baldoni, Gary; Topping, Stephen; Lingertat, Helmut; Sarin, Vinod K.; Shah, Kanai S.

    2011-01-01

    In this paper we report on the fabrication and characterization of SrHfO3:Ce ceramics. Powders were prepared by solid-state synthesis using metal oxides and carbonates. X-ray diffraction measurements showed that phase-pure SrHfO3 is formed at 1200°C. Inductively coupled plasma spectroscopy confirmed the purity and composition of each batch. SrHfO3 exhibits several phase changes in the solid, but this does not appear to be detrimental to the ceramics. Microprobe experiments showed uniform elemental grain composition, whereas aluminum added as charge compensation for trivalent cerium congregated at grain boundaries and triple points. Radioluminescence spectra revealed that the light yield decreases when the concentration of excess Sr increases. The decrease in the light yield may be related to the change of Ce3+ into Ce4+ ions. For stoichiometric SrHfO3:Ce, the light yield is about four times that of bismuth germanate (BGO), the conventional benchmark, indicating great potential for many scintillator applications. PMID:21339835

  4. Effects of fluorine doping on thermoelectric properties of Sr0.61Ba0.39Nb2O6 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Yi; Liu, Jian; Wang, Zhen; Zhou, YuCheng; Wang, Chunlei; Li, Jichao; Zhu, Yuanhu; Li, Maokui; Mei, Liangmo

    2015-02-01

    The thermoelectric properties of Sr0.61Ba0.39Nb2O6 ceramics, doped with different contents of fluorine at the oxygen sites, were investigated in the temperature range of 323 to 1073 K. The electrical resistivity is reduced significantly after fluorine doping. However, the magnitudes of electrical resistivity, Seebeck coefficient (S), and slope of S at high temperatures (dS/dT) vary non-monotonically with increasing doping contents, indicating that doped fluorine ions not only act as electron donors, but also influence band structure. The lattice thermal conductivity decreases when fluorine ions are slightly doped, and increases with increasing fluorine content because of the increasing average grain size. The thermoelectric performance is enhanced by slight fluorine doping due to the increase of the power factor and the reduction of thermal conductivity. The thermoelectric figure of merit reaches maximum value (0.21 at 1073 K) in the Sr0.61Ba0.39Nb2O5.95F0.05 sample.

  5. 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

  6. Au and Pd nanoparticles supported on CeO2, TiO2, and Mn2O3 oxides

    NASA Astrophysics Data System (ADS)

    Nascente, P. A. P.; Maluf, S. S.; Afonso, C. R. M.; Landers, R.; Pinheiro, A. N.; Leite, E. R.

    2014-10-01

    Gold and palladium nanoparticles were incorporated on CeO2, TiO2, and Mn2O3 supports prepared by a sol-gel method. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution TEM (HRTEM), scanning TEM (STEM) in high angle annular dark field mode (HAADF), and energy filtered TEM (EFTEM) using electron energy loss spectroscopy (EELS). The XRD diffractograms presented sharp and intense peaks indicating that the samples are highly crystalline, but it did not detected any peak corresponding to Au or Pd phases. This indicates that the Au and Pd NPs were incorporated into the structures of the oxides. It was not possible to obtain an Au 4f spectrum for Au/Mn2O3 due to an overlap with the Mn 3p spectrum. The XPS Au 4f spectra for Au/CeO2 and Au/TiO2 present negative chemical shifts that could be attributed to particle-size-related properties. The XPS Pd 3d spectra indicate that for both CeO2 and TiO2 substrates, the Pd NPs were in the metallic state, while for the Mn2O3 substrate, the Pd NPs were oxidized. The HRTEM results show the formation of nanocrystalline oxides having particles sizes between 50 and 200 nm. TEM micrographs show that the addition of Au caused the formation of Au clusters in between the CeO2 NPS, formation of Au NPs for the TiO2 support, and homogeneous distribution of Au clusters for the Mn2O3 support. The addition of Pd yielded a homogeneous dispersion throughout the CeO2 and TiO2, but caused the formation of Pd clusters for the Mn2O3 support.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Field induced polarization and magnetization behaviour of Gd-doped lead magnesium niobate ceramics

    NASA Astrophysics Data System (ADS)

    Pandey, Adityanarayan; Gupta, Surya Mohan; Nigam, Arun Kumar

    2016-05-01

    Both superparaelectric and superparamagnetic behaviour has been observed in rare earth magnetic ion Gd3+ doped Lead Magnesium Niobate (Gd-PMN). Field induced polarization and magnetization studies reveal hystresis loss free P-E and M-H loop at 300K and 5K, respectively. Temperature dependence of inverse susceptibility plot shows deviation at a temperature "td" when fitted with the Curie-Weiss law. This deviation has been attributed to transition from paramagnetic to superparamagnetic behaviour as reported in amorphous Pd-Ni-Fe-P alloys.

  14. 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

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. Influence of laser power on the orientation and microstructure of CeO 2 films deposited on Hastelloy C276 tapes by laser chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Pei; Ito, Akihiko; Tu, Rong; Goto, Takashi

    2010-08-01

    CeO 2 films were prepared on LaMnO 3/MgO/Gd 2Zr 2O 7 multi-coated Hastelloy C276 tapes by laser chemical vapor deposition at different laser power ( PL) from 46 to 101 W. Epitaxial (1 0 0) CeO 2 films were prepared at PL = 46-93 W (deposition temperature, Tdep = 705-792 K). Epitaxial CeO 2 films had rectangular-shaped grains at PL = 46-77 W ( Tdep = 705-754 K), while square-shaped grains were obtained at PL = 85-93 W ( Tdep = 769-792 K). CeO 2 films showed a columnar microstructure. Epitaxial (1 0 0) CeO 2 films with rectangular grains exhibited full width at half maximum of ω-scan on (2 0 0) reflection and ϕ-scan on (2 2 0) reflection of 3.4-3.2° and 6.0-7.2°, respectively. The deposition rate of the epitaxial (1 0 0) CeO 2 films had a maximum of 4.6 μm h -1 at PL = 77 W ( Tdep = 754 K).

  20. Optical study of the effect of the impurity content on the ferroelectric properties of Er3+ doped SBN glass-ceramic samples

    NASA Astrophysics Data System (ADS)

    Haro-González, P.; Martín, L. L.; Pérez-Rodríguez, C.; Martín, I. R.; Mujica, A.

    2011-10-01

    Photoluminescence measurements have been performed on glass ceramic samples of strontium barium niobate doped with Er3+. The glass-ceramic samples were obtained from the precursor glass by thermal treatment and were doped with different contents of Er3+ ions. The average size of the nanocrystals in the samples was about 50 nm. The optical properties of the Er3+ ions were studied upon 532 nm excitation and the luminescence changes were measured as a function of temperature. The study of the luminescence spectra with increasing temperature has allowed us to ascertain the occurrence of the ferroelectric-paraelectric phase transition in the strontium barium niobate nanocrystals embedded in the glass matrix. We have particularly focused on the temperature range around the Curie temperature, when the system undergoes the transition from the ferroelectric phase to the paraelectric phase. Doping of the strontium barium niobate samples results in a change in the measured value of the Curie temperature which induces a change in the ferroelectric properties. It is interesting to note that this phase transition in the nanocrystals immersed in the glass matrix had previously not been detected.

  1. 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.

  2. Reduction of the 1.55 µm Er3+ emission band half-width in Er doped and Er/Yb co-doped oxy-fluoride glass-ceramics fibers

    NASA Astrophysics Data System (ADS)

    Augustyn, E.; Żelechower, M.; Czerska, E.; Świderska, M.; Sozańska, M.

    2014-05-01

    In earlier papers the authors have shown by XRD measurements and HRTEM imaging/SAED (selected area electron diffraction)/STEM imaging/EDS X-ray spectra that erbium or erbium/ytterbium-enriched nano-crystals are formed in erbium doped and erbium/ytterbium co-doped oxy-fluoride glass-ceramics fibers by their controlled heat-treatment. By the analysis of XRD, HRTEM and SAED patterns three crystalline compounds have been identified (Pb5Al3F19, Er4F2O11Si3, Er3FO10Si3). Additionally, STEM imaging combined with EDS X-ray analysis revealed higher erbium/ytterbium content in nano-crystals than in glassy host. According to several reports on homogeneous/inhomogeneous broadening of emission lines we can expect in glass-ceramics material the distinct reduction of the 1.55 μm Er3+ linewidth (FWHM) as a consequence of structurally ordered (crystalline) vicinity of erbium ions in glass-ceramics fibers. Additionally the Stark splitting of Er3+ ions sub-levels should be observed due to the crystalline electric field surrounding the erbium ion, which lifts the atomic state degeneracy, however identified crystals possess rather low symmetry (monoclinic or triclinic unit cell).

  3. Efficient ceramic anodes infiltrated with binary and ternary electrocatalysts for SOFCs operating at low temperatures

    NASA Astrophysics Data System (ADS)

    Hussain, A. Mohammed; Høgh, Jens V. T.; Zhang, Wei; Bonanos, Nikolaos

    2012-10-01

    Electrocatalyst precursor of various combinations: Pt, Ru, Pd, Ni and Gd-doped CeO2 (CGO) were infiltrated into a porous Sr0.94Ti0.9Nb0.1O3 (STN) backbone, to study the electrode performance of infiltrated ceramic anodes at low temperature ranges of 400-600 °C. The performance of the binary electrocatalyst infiltrated ceramic backbones are Pt-CGO>Ru-CGO>Pd-CGO>Ni-CGO. Ternary electrocatalyst of Ni-Pd-CGO and Ni-Pt-CGO showed the lowest polarization resistance of 0.31 and 0.11 Ωcm2, respectively at 600 °C in H2/3% H2O. The average particle size of the ternary electrocatalyst was larger than the binary Pd-CGO and Pt-CGO due to the particle coarsening of Ni nanoparticles. High resolution transmission electron microscopic analysis on the best performing Ni-Pt-CGO electrocatalyst infiltrated anode reveals the formation of Ni-Pt nanocrystalline alloy and a homogenous distribution of nanoparticles on STN backbone.

  4. 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.)

  5. 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.

  6. Dielectric, multiferroic properties and resistance modulation of Ta-doped Bi0.97Ba0.03FeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Wang, X.; Wang, S. Y.; Liu, W. F.; Guo, F.; Xi, X. J.; Wang, H. J.; Li, D. J.

    2014-02-01

    Single phase Bi0.97Ba0.03Fe1-xTaxO3 ceramics with x = 0, 0.01, 0.03, 0.05 were synthesized by modified rapid sintering process method. The formation of rhombohedral perovskite-like structure was confirmed by X-ray diffraction investigation for all the samples. Dielectric and leakage current measurements indicated that the content of the oxygen vacancy in the samples decreased as a function of the substitution of Ta5+ ions. A distinct threshold switching behavior was observed in the leakage current density. The impedance measurements suggested that the grain effect made a major contribution to the resistance. The changes in dielectric, multiferroic properties and resistance modulation of the Ta5+ and Ba2+ co-doped BiFeO3 ceramics could have a huge potential for material application.

  7. Characterization of Sm-Doped Ceria Ceramics Synthesized by Two Different Methods

    NASA Astrophysics Data System (ADS)

    Arabaci, Aliye; Serin, Özgün

    2015-07-01

    Ceria-based materials have attracted much attention as electrolyte materials for low and intermediate temperature solid oxide fuel cells (SOFCs). In this study, we examined the effect of synthesis method on the microstructure and the ionic conductivity of ceria-based electrolytes. Sm0.2Ce0.8O1.9 (SDC) electrolytes for SOFCs were prepared using the Pechini and cellulose templating (CT) methods. Microstructures of the calcined and sintered samples were characterized by XRD and SEM techniques. The XRD results indicate that a single-phase fluorite structure formed at the relatively low calcination temperature of 500 °C. The relative densities of the sintered pellets were higher than 90%, which was proved by the SEM images. Calcined powders were characterized by FTIR technique. The electrical properties of the samarium-doped ceria electrolytes were analyzed by electrochemical impedance spectroscopy. The total ionic conductivities are 3.02 × 10-2 and 3.42 × 10-2 S/cm at 750 °C for the SDC electrolytes prepared by the Pechini method and the CT method, respectively.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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

  13. Mechanical Properties and Corrosion Behavior of CeO2 and SiC Incorporated Al5083 Alloy Surface Composites

    NASA Astrophysics Data System (ADS)

    Amra, M.; Ranjbar, Khalil; Dehmolaei, R.

    2015-08-01

    In this investigation, nano-sized cerium oxide (CeO2) and silicon carbide (SiC) particles were stirred and mixed into the surface of an Al5083 alloy rolled plate using friction stir processing (FSP) to form a surface nano-composite layer. For this purpose, various volume ratios of the reinforcements either separately or in the combined form were packed into a pre-machined groove on the surface of the plate. Microstructural features, mechanical properties, and corrosion behavior of the resultant surface composites were determined. Microstructural analysis, optical microscopy and scanning electron microscopy, showed that reinforcement particles were fairly dispersed inside the stir zone and grain refinement was gained. Compared with the base alloy, all of the FSP composites showed higher hardness and tensile strength values with the maximum being obtained for the composite containing 100% SiC particles, i.e., Al5083/SiC. The corrosion behavior of the samples was studied by conducting potentiodynamic polarization tests and assessed in terms of corrosion potential, pitting potential, and passivation range. The result shows a significant increase in corrosion resistance of the base alloy; i.e., the longest passivation range when CeO2 alone was incorporated into the surface by acting as cathodic inhibitors. Composites reinforced with SiC particles exhibited lower pitting resistance due to the formation of microgalvanic couples between cathodic SiC particles and anodic aluminum matrix. The study was aimed to fabricate metal matrix surface composites with improved hardness, tensile strength, and corrosion resistance by the incorporation of CeO2 and SiC reinforcement particles into the surface of Al5083 base alloy. Optimum mechanical properties and corrosion resistance were obtained for the FSP composite Al5083/(75%CeO2 + 25%SiC). In this particular FSP composite, hardness and tensile strength were increased by 30, and 14%, respectively, and passivation range was increased to 0.19 V/SCE compared to the base alloy with no passivation range.

  14. Extracellular polymeric substances (EPS) of freshwater biofilms stabilize and modify CeO2 and Ag nanoparticles.

    PubMed

    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

  15. 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.

  16. A spray drying system for synthesis of rare-earth doped cerium oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Sharma, Vaneet; Eberhardt, Kathryn M.; Sharma, Renu; Adams, James B.; Crozier, Peter A.

    2010-08-01

    We have constructed a spray dryer to synthesize doped ceria nanoparticles. The system was employed to synthesize mixed oxide nanoparticles of praseodymium doped CeO 2 (Ce 0.97Pr 0.03O 2, Ce 0.90Pr 0.10O 2, and Ce 0.80Pr 0.20O 2). X-ray diffraction confirmed the fluorite-like cubic crystal structure of the synthesized materials after heat treatment at 700 °C for 2 h. As-dried CeO 2 samples were found to have an average particle size of (6.0 ± 0.2) nm which increased to (17.0 ± 0.4) nm after heat treatment with an improvement in crystallinity. The particle size increased steadily with Pr content. The lattice parameter of Pr-doped CeO 2 was found to increase or decrease with Pr content depending on the heat treatment process.

  17. 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.

  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. PMID:24231324

  19. Study of vanadium doped strontium bismuth niobate tantalate ferroelectric ceramics and thin films

    NASA Astrophysics Data System (ADS)

    Wu, Yun

    First part of the dissertation is the research on the material system strontium bismuth niobate vanadates, SrBi2(Nb,V)2O 9, (SBNV) ferroelectrics. Present research includes two parts: (1) enhancement of ferroelectric and dielectric properties through partial vanadium substitution and (2) thin films of SBNV ferroelectrics by sol-gel processing. The experimental results demonstrated that the partial incorporation of vanadium into the crystal structure resulted in a significantly enhanced ferroelectric and dielectric properties, which include approximately 300% increase in remanent polarization and 100% reduction in coercive field. Such a significant property enhancement was attributed to the fact that the incorporation of V 5+ with smaller radius (58 pm), in comparison with that of Nb 5+ (69 pm), resulted in an increased "rattling space" for spontaneous polarization. It was also found that the incorporation of vanadium improved other properties of the ferroelectrics including reduced DC conductivity and tangent loss. In addition, some preliminary work has been done on the sol-gel processing and film deposition of SBNV ferroelectrics. A sol-gel process has been successfully developed and single phase SBNV ferroelectrics have been obtained after heat treatment at 600--800°C. Smooth dense thin films of SBNV ferroelectrics with an average grain size of ˜100 nm were obtained through sol-gel coating. Second part of the dissertation is the study on the influence of the vanadium doping on the strontium bismuth tantalate, SrBi2Ta2O9, (SBT) system. Partial substitution (10 at%) of pentavalent tantalum ions by pentavalent vanadium ions with a relatively smaller ionic radius in the SBT layered perovskite ferroelectrics leads to an enhanced dielectric constants, a broadened peak, and a reduced stability of layered tetragonal perovskite structure, as evidenced by an increased para-ferroelectric transition temperature. It was found that the frequency dependence of para

  20. 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.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. Microstructure and electrical transport in nano-grain sized Ce 0.9Gd 0.1O 2-δ ceramics

    NASA Astrophysics Data System (ADS)

    Ruiz-Trejo, Enrique; Santoyo-Salazar, Jaime; Vilchis-Morales, Ruben; Benítez-Rico, Adriana; Gómez-García, Francisco; Flores-Morales, Carlos; Chávez-Carvayar, José; Tavizón, Gustavo

    2007-11-01

    An enhancement of the electrical conductivity has been found in nano-grain sized Ce 0.9Gd 0.1O 2-δ ceramics when measured in N 2 ( p=3.5×10 -6 atm) in comparison with the most commonly accepted values of bulk ionic conductivity. We first present the synthesis and characterisation of the nanoparticles later used for the preparation of dense nanoceramics of Gd-doped CeO 2. The nanoparticles were characterised by X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The good sintering properties of these nanopowders allowed us to obtain very dense ceramics (>90% theoretical density) while keeping the grain size close to 100 nm. The microstructure of these nanoceramics was analysed by AFM and scanning electron microscopy (SEM) while the electrical characterisation was performed by the 4-point dc technique between 500 and 950 °C in air or N 2 and ac impedance between 150 and 400 °C in air and or argon. We briefly discuss the possibilities of electron vs. oxygen ion conduction and grain boundary vs. bulk conductivity. The features exhibited by these ceramics represent an increased potential to process solid electroceramics materials with specific levels of electronic and/or ionic conductivities for a variety of electrochemical devices.

  6. Enhanced piezoelectricity and photoluminescence in Dy-doped Ba0.85Ca0.15Ti0.9Zr0.1O3 lead-free multifunctional ceramics

    NASA Astrophysics Data System (ADS)

    Lei, Fengying; Jiang, Na; Luo, Lingling; Guo, Yongquan; Zheng, Qiaoji; Lin, Dunmin

    2015-12-01

    Lead-free multifunctional ceramics of Ba0.85Ca0.15Ti0.9Zr0.1O3-x mol% Dy have been prepared by an ordinary sintering method and the effects of Dy2O3 doping on structure, piezoelectric, ferroelectric and photoluminescent properties of the ceramics have been studied. The ceramics possess a single phase perovskite structure. The grain growth of the ceramics is prohibited and the ferroelectric-paraelectric phase transition at TC becomes more diffusive after the addition of Dy2O3. Dy2O3 doping improves the piezoelectricity of the ceramics and the optimal piezoelectric properties d33 = 335 pC/N is obtained at x = 0.5. The addition of 2 mol% Dy enhances the photoluminescent properties of the ceramics and strong emissions at ˜ 478 nm and ˜ 575 nm are observed. Our study shows that the ceramics with low Dy2O3 levels exhibit simultaneously the strong piezoelectricity, ferroelectricity and photoluminescence and may have a potential application in mechano-electro-optic integration and coupling device.

  7. 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.

  8. 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.

  9. Effect of Thermal Treatment on the Textural Properties of CeO2 Powders Synthesized in Near- and Supercritical Alcohols.

    PubMed

    Slostowski, Cédric; Marre, Samuel; Babot, Odile; Toupance, Thierry; Aymonier, Cyril

    2015-11-16

    CeO2 nanocrystals (NCs) have attracted increasing interest over the past few years, in particular for their use in catalytic reactions. Syntheses mediated by near- and supercritical alcohols have proven to be innovative ways to obtain CeO2 NCs with controlled crystallite sizes (from 3 to 8 nm depending on the alcohol) and surface functionalities, with alcohol moieties. When submitted to a thermal treatment at 500 °C, required to desorb/degrade surface organic species, these powders displayed different behaviors depending on the alcohol used during the synthesis. Cerium oxide powders synthesized in sc-MeOH, sc-EtOH and sc-iPrOH undergo sintering during treatment at 500 °C, with a decrease of their specific surface area. Conversely, those synthesized in sc-BuOH, nc-PentOH and nc-HexOH keep their initial crystallite sizes and morphology, but show a great enhancement of their specific surface area (up to 200 m(2) g(-1)), which is unprecedented after such a thermal treatment. PMID:26333851

  10. Fluorinated Cerium(IV) Enaminolates: Alternative Precursors for Chemical Vapor Deposition of CeO2 Thin Films.

    PubMed

    Schläfer, J; Graf, D; Fornalczyk, G; Mettenbörger, A; Mathur, S

    2016-06-01

    High-yield synthesis of four new fluorinated enaminones LH2 (RfC(O)C2H2NH)2C2H4 (Rf = CF3 (2a), C2F5 (2b), C3F7 (2c)) and (F3CC(O)C2H2NH)2C3H6 (2a') as dianionic ligands is described. The ligands were characterized in solution (via nuclear magnetic resoannce (NMR)) as well as in the solid state (via X-ray diffraction (XRD)). The ligating ability of the enaminones was verified by reacting them with [Ce2(O(i)Pr)8(HO(i)Pr)2], which resulted in monomeric cerium(IV) complexes [CeL2] (3a-c, 3a') based on tetradentate chelation of the ligands. Cerium enaminolates were comprehensively analyzed by NMR spectroscopy, mass spectrometry, and single-crystal XRD studies to verify their monomeric nature. High stability under ambient conditions and high volatility makes them a potential precursor for the gas-phase synthesis of CeO2. Complexes 3a and 3b were applied as precursors in thermal and plasma-enhanced chemical vapor deposition to obtain crystalline ceria films with different surface morphologies. The purity and surface states of the films were analyzed by X-ray photoelectron spectroscopy, which revealed a high amount of Ce(3+) on the subsurface of CeO2 films. PMID:27159551

  11. Enhanced blue light shielding property of light-diffusion polycarbonate composites by CeO2-coated silicate microspheres

    NASA Astrophysics Data System (ADS)

    Zhao, Yu; Shi, Liyi; Tang, Anjie; Song, Na; Tang, Shengfu; Ding, Peng

    2015-07-01

    The CeO2 coated silicate microspheres (SMSs) core-shell particles (SMS-CeO2) were synthesized for enhancing blue light shielding property of polycarbonate (PC) composites. The structure analysis showed that CeO2 particles were homogenously coated on SMS by Ce-O-Si bonds. The optical analysis indicated that the transmittance of PC/SMS-CeO2 composites were enhanced to 63.2% from 42.9% for PC/SMS/CeO2 composites when 0.6 wt.% fillers were loaded, while there was no obvious influence on the haze of the composites. UV-Vis analysis showed that the absorbance at 450-nm wavelength of blue-light increased from 24% of PC/SMS to 50% of PC/SMS-CeO2 composites, while the absorbance at 650-nm wavelength of red-light was unchanged. These results indicated that the PC/SMS-CeO2 composites had blue light shielding property and better performance on transmitting other visible lights.

  12. 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.

  13. 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. PMID:25080384

  14. 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.

  15. 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

  16. 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.

  17. 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. PMID:17957316

  18. 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

  19. 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

    2016-03-16

    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. PMID:26910311

  20. 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. PMID:25983225

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. Photoluminescence and energy transfer in Tb{sup 3+}/Mn{sup 2+} co-doped ZnAl{sub 2}O{sub 4} glass ceramics

    SciTech Connect

    Lakshminarayana, Gandham; Wondraczek, Lothar

    2011-08-15

    We report on Tb{sup 3+} as efficient sensitizer for red photoemission from Mn{sup 2+}-centers in ZnO-B{sub 2}O{sub 3}-Al{sub 2}O{sub 3}-Si{sub 2}O-Na{sub 2}O-SrO glasses and corresponding gahnite glass ceramics. In comparison to singly or co-doped glasses, the glass ceramics exhibit significantly increased emission intensity. Structural considerations, ESR, and dynamic luminescence spectroscopy indicate partial incorporation of Mn{sup 2+} as well as Tb{sup 3+} into the crystalline phase, the former on octahedral Zn{sup 2+}-sites. Interionic distance and charge transfer probability between both species depend on crystallization conditions. This enables control of the energy transfer process and, hence, tunability of the color of photoemission by simultaneous emission from Tb{sup 3+} and Mn{sup 2+} centers. Concentration quenching in Mn{sup 2+}-singly doped materials was found at a critical dopant concentration of about 1.0 mol%. The energy transfer process was studied in detail by dynamic as well as static luminescence spectroscopy. Spectroscopic results suggest the application of the studied materials as single or dual-mode emitting phosphor for luminescent lighting. - Graphical abstract: In the prepared Tb{sup 3+}/Mn{sup 2+} codoped glass ceramics containing gahnite (ZnAl{sub 2}O{sub 4}) nanocrystals, the luminescence color is changed from green light to yellowish-red light with an increase in Mn{sup 2+} concentration due to enhanced energy transfer from Tb{sup 3+} to Mn{sup 2+} ions. This tunability should have potential applications in solid state lighting to produce white light, which can be obtained by appropriately optimizing the ratio of Tb{sup 3+}/Mn{sup 2+} ions under UV(350 nm) excitation. Highlights: > Photoluminescence from Mn{sup 2+} and Tb{sup 3+} singly and co-doped glasses and gahnite glass ceramics was studied. > Occurrence of energy transfer from Tb{sup 3+} to Mn{sup 2+} was confirmed. > Luminescence color tunability is achieved by varying dopant

  6. 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.

  7. Atomic-scale observation of the grain-boundary structure of Yb-doped and heat-treated silicon nitride ceramics

    SciTech Connect

    Ziegler, A.; Cinibulk, M. K.; Kisielowski, C.; Ritchie, R. O.

    2007-10-01

    The effect of secondary sintering additives and/or a post-sintering heat treatment on the semicrystalline atomic structure of the intergranular phase in silicon nitride ceramics is investigated. Three different Yb-doped Si{sub 3}N{sub 4} ceramic compositions are examined using a scanning transmission electron microscope, whereby the intergranular atomic structure is directly imaged with A ring ngstrom resolution. The resulting high-resolution images show that the atomic arrangement of the Yb takes very periodic positions along the interface between the intergranular phase and the matrix grains, and that a postsintering 1250 deg. C heat treatment, as well as a change of the secondary sintering additives (Al{sub 2}O{sub 3} vs SiO{sub 2}), does not alter the atomic positions of Yb. This result has implications for the understanding of how the mechanical properties of ceramics are influenced by the presence of the nanoscale intergranular phase, and for associated computational modeling of its precise role and atomic structure.

  8. 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+.

  9. Improved multiferroic properties of La-doped 0.6BiFeO3—0.4SrTiO3 solid solution ceramics

    NASA Astrophysics Data System (ADS)

    Ma, Zheng-Zheng; Li, Jian-Qing; Tian, Zhao-Ming; Qiu, Yang; Yuan, Song-Liu

    2012-10-01

    The 0.6(Bi1-xLax)FeO3—0.4SrTiO3 (x = 0, 0.1) multiferroic ceramics are prepared by a modified Pechini method to study the effect of substitution of SrTiO3 and La in BiFeO3. The X-ray diffraction patterns confirm the single phase characteristics of all the compositions each with a rhombohedral structure. The magnetic properties of the ceramics are significantly improved by a solid solution with SrTiO3 and substitution of La. The values of the dielectric constant ɛr and loss tangent tan δ of all the samples decrease with increasing frequency and become constant at room temperature. The La-doped 0.6BiFeO3—0.4SrTiO3 ceramics exhibit improved dielectric and ferroelectric properties, with higher dielectric constant enhanced remnant polarization (Pr) and lower leakage current at room temperature. Compared with a anti-ferromagnetic BiFeO3 compound, the 0.6(Bi0.9La0.1)FeO3—0.4SrTiO3 sample shows the optimal ferromagnetism with remnant magnetization Mr ~ 0.135 emμ/g and ferroelectricity with Pr ~ 5.94 μC/cm2 at room temperature.

  10. Preparation and properties of ceramic interconnecting materials, La 0.7Ca 0.3CrO 3- δ doped with GDC for IT-SOFCs

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaoliang; Ma, Jianjun; Deng, Feijun; Meng, Guangyao; Liu, Xingqin

    One of the challenges for improving the performance and cost-effectiveness of solid oxide fuel cells (SOFCs) is the development of effective interconnect materials. A widely used interconnect ceramic for SOFCs is doped lanthanum chromite. In this paper, we report a doped lanthanum chromite, La 0.7Ca 0.3CrO 3- δ (LCC) + x wt.% Gd 0.2Ce 0.8O 1.9 (GDC) (x = 0-10), with improved electrical conductivity and sintering capability. In this composite material system, LCC + GDC were prepared by an auto-ignition process and the electrical conductivity was characterized in air and in H 2. The LCC powders exhibited a better sintering ability and could reach a 94.7% relative density at 1400 °C for 4 h in air and with the increase of GDC content the relative density increased, reached 98.5% when the GDC content was up to 10 wt.%. The electrical conductivity of the samples dramatically increased with GDC addition until a maximum of 134.48 S cm -1 in air at 900 °C when the materials contained 3 wt.% GDC. This is 5.5 times higher than pure LCC (24.63 S cm -1). For the sample with a 1 wt.% GDC content, the conductivity in pure H 2 at 900 °C was a maximum 5.45 S cm -1, which is also higher than that of pure LCC ceramics (4.72 S cm -1). The average thermal expansion coefficient (TEC) increased with the increase of GDC content, ranging from 11.12 to 14.32 × 10 -6 K -1, the majority of which unfortunately did not match that of 8YSZ. The oxygen permeation measurement presented a negligible oxygen ionic conduction, indicating that it is still an electronically conducting ceramic. Therefore, it is a very promising interconnect material for higher performance and cost-effectiveness for SOFCs.

  11. High Pressure Studies on (111)-Terminated CeO2 Nano-Octahedrons: The Major Effect of Non-Hydrostatic Conditions

    NASA Astrophysics Data System (ADS)

    Bo, Liu; Quanjun, Li; Ran, Liu; Mingguang, Yao; Bingbing, Liu

    2013-06-01

    The effect of nonhydrostatic conditions on high pressure phase transition on (111)-terminated CeO2 nano-octahedrons were studied using in situ high-pressure Raman spectroscopy. Under non-hydrostatic conditions (with no pressure medium) the CeO2 nano-octahedrons underwent a reversible phase transition from fluorite phase to α-PbCl2 phase at 26 GPa, which is lower than the bulk counterpart. In contrast, in our previous research, the CeO2 nano-octahedrons under hydrostatic conditions are shown to be more stable than the bulk, which is driven by lower compressibility of the exposed (111) planes. The transition pressure from cubic to orthorhombic phase is approximately 3 GPa higher than bulk materials. Further analysis shows that lager stress existing in the grain boundaries is believed to major factor to reduce the phase transition under non-hydrostatic conditions.

  12. Influence of the Ion-to-Atom Ratio on the Structure of CeO2 Buffer Layer by Ion Beam Assisted E-Beam Evaporation

    NASA Astrophysics Data System (ADS)

    Kim, Chang Su; Jo, Sung Jin; Kim, Woo Jin; Koo, Won Hoe; Baik, Hong Koo; Lee, Se Jong

    2005-09-01

    Using ion-beam assisted e-beam evaporation with the ion beam directed at 55° to the normal of the film plane, (200) oriented CeO2 films with biaxial texture were deposited on Hastelloy C276 substrates at room temperature. The crystalline quality and in-plane orientation of films was investigated by X-ray diffraction 2θ-scan and Φ-scan, atomic force microscopy (AFM). It was shown that the in-plane and out-of-plane textures of the CeO2 films were controlled by the deposition parameters. The orientation of the films was studied as a function of ion-to-atom ratio and film thickness. The ion-to-atom ratio was varied by independently adjusting the deposition rate and the ion current density. Under optimum condition, (200) textured CeO2 films have been successfully grown on Hastelloy C276.

  13. 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.

  14. 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.

  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. 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.

  17. 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). PMID:26767436

  18. Structure and intense UV up-conversion emissions in RE3+-doped sol-gel glass-ceramics containing KYF4 nanocrystals

    NASA Astrophysics Data System (ADS)

    Yanes, A. C.; Santana-Alonso, A.; Méndez-Ramos, J.; del-Castillo, J.

    2013-12-01

    Transparent nano-glass-ceramics containing KYF4 nanocrystals were successfully obtained by the sol-gel method, doped with Eu3+ and co-doped with Yb3+ and Tm3+ ions. Precipitation of cubic KYF4 nanocrystals was confirmed by X-ray diffraction and high-resolution transmission electron microscope images. Excitation and emission spectra let us to discern between ions into KYF4 nanocrystals and those remaining in a glassy environment, supplemented with time-resolved photoluminescence decays, that also clearly reveal differences between local environments. Unusual high-energy up-conversion emissions in the UV range were obtained in Yb3+-Tm3+ co-doped samples, and involved mechanisms were discussed. The intensity of these high-energy emissions was analyzed as a function of Yb3+ concentration, heat treatment temperature of precursor sol-gel glasses and pump power, determining the optimum values for potential optical applications as highly efficient UV up-conversion materials in UV solid-state lasers.

  19. 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.

  20. Electro-caloric effect in lead-free Sn doped BaTiO{sub 3} ceramics at room temperature and low applied fields

    SciTech Connect

    Upadhyay, Sanjay Kumar; Reddy, V. Raghavendra E-mail: vrreddy@csr.res.in; Bag, Pallab; Rawat, R.; Gupta, S. M.; Gupta, Ajay

    2014-09-15

    Structural, dielectric, ferroelectric (FE), {sup 119}Sn Mössbauer, and specific heat measurements of polycrystalline BaTi{sub 1–x}Sn{sub x}O{sub 3} (x = 0% to 15%) ceramics are reported. Phase purity and homogeneous phase formation with Sn doping is confirmed from x-ray diffraction and {sup 119}Sn Mössbauer measurements. With Sn doping, the microstructure is found to change significantly. Better ferroelectric properties at room temperature, i.e., increased remnant polarization (38% more) and very low field switchability (225% less) are observed for x = 5% sample as compared to other samples and the results are explained in terms of grain size effects. With Sn doping, merging of all the phase transitions into a single one is observed for x ≥ 10% and for x = 5%, the tetragonal to orthorhombic transition temperature is found close to room temperature. As a consequence better electro-caloric effects are observed for x = 5% sample and therefore is expected to satisfy the requirements for non-toxic, low energy (field) and room temperature based applications.

  1. 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.

  2. Effect of lanthanum doping on the structural, ferroelectric, and strain properties of Bi1/2(Na0.82K0.18)1/2TiO3 lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Dinh, Thi Hinh; Lee, Hyun-Young; Yoon, Chang-Ho; Malik, Rizwan Ahmed; Kong, Young-Min; Lee, Jae-Shin; Tran, Vu Diem Ngoc

    2013-04-01

    To clarify the effect of A-site donor doping on the phase transition and the strain enhancement, we investigated the crystal structure, as well as the piezoelectric, ferroelectric and electric-field-induced strain (EFIS) properties of La-doped Bi1/2(Na0.82K0.18)1/2TiO3 (BNKT) ceramics. Similarly to our previous studies on BNKT doped with B-site donors such as Nb and Ta, La doping was found to induce a ferroelectric-to-nonpolar (FE-NP) phase transition, leading to a large enhancement in EFIS just after the transition. The result provides strong evidence that a close relationship exists between the Goldschumidt's tolerance factor and the FE-NP transition in BNKT, which has been observed in B-site-donor or isovalent impurity-doped BNKT.

  3. 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.

  4. Epitaxial CeO2 buffer layers for YBa2Cu3O(7-delta) films on sapphire

    NASA Astrophysics Data System (ADS)

    Maul, M.; Schulte, B.; Haeussler, P.; Frank, G.; Steinborn, T.; Fuess, H.; Adrian, H.

    1993-08-01

    The paper reports the successful in situ preparation of thin epitaxial CeO2 buffer layers and YBa2Cu3O(7-delta) (YBCO) films on (1 -1 0 2) Al2O3 substrates by electron beam coevaporation, using an evaporation system (Leybold L560) with four sources. Electron beam sources were used for Y, Ba, and Ce, while Cu was evaporated from a resistively heated tungsten boat. The buffer layers show very smooth surfaces and structural properties close to those of a single crystal. High quality YBCO films grown on these buffer layers have Tc not 88 K or above and j(c) values of 10 exp 6 A/sq cm or greater.

  5. On the adsorption and formation of Pt dimers on the CeO2(111) surface

    NASA Astrophysics Data System (ADS)

    Bruix, Albert; Nazari, Fariba; Neyman, Konstantin M.; Illas, Francesc

    2011-12-01

    The direct adsorption of Pt2 dimers on CeO2(111) and their formation from isolated adsorbed Pt atoms have been studied using periodic slab model calculations based on density functional theory and including the so-called on-site Hubbard parameter (GGA + U). In the most stable configuration Pt2 is found to be almost parallel to the surface; the electronic ground state is closed shell and there is no evidence of charge transfer towards or from the surface. The formation of Pt2 from two single adsorbed Pt atoms involves a rather small energy barrier of ˜0.10 eV only. On the contrary, dissociation of adsorbed Pt2 requires to overcome a considerable barrier of ˜1.43 eV. This indicates that once Pt2 is formed it will remain on the surface, thus likely triggering the growth of larger supported Pt particles.

  6. 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

  7. Application of the method of increments to the adsorption of CO on the CeO2(110) surface

    NASA Astrophysics Data System (ADS)

    Müller, Carsten; Herschend, Björn; Hermansson, Kersti; Paulus, Beate

    2008-06-01

    We have combined an embedded-cluster model with an extension of the method of increments to treat the adsorption of molecules on a surface. In this way we are able to investigate the physisorption of CO on CeO2(110) at the MP2, MP4(SDTQ), and CCSD(T) levels with only moderate computational costs. We find that, at the CCSD(T) level, 25% of the adsorption energy originates from electron correlation. The interactions of the CO molecule with its five nearest cerium and oxygen neighbors in the surface layer make the largest contributions to the electron correlation. Approximately 97% of the adsorption-induced electron correlation energy part of the adsorption energy is recovered by the method of increments (in our chosen expansion), at the MP2 level.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. Effect of tetragonal distortion on ferroelectric domain switching: A case study on La-doped BiFeO3-PbTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Leist, Thorsten; Granzow, Torsten; Jo, Wook; Rödel, Jürgen

    2010-07-01

    The ferroelectric and piezoelectric properties of (1-x)BiFeO3-xPbTiO3 (BF-PT) ceramics were investigated as a function of tetragonal distortion. The latter was adjusted by employing La-doping (0-30 at %) while keeping the material near the morphotropic phase boundary by varying x between 0.35 and 0.46. This allows changing the c/a ratio of tetragonal BF-PT in the range from 1.10-1.01 and consequently alters the level of compatibility stresses. It was found that the c/a ratio has a significant influence on domain switching as inferred from electric field induced polarization, strain hysteresis, and Rayleigh measurements. Specifically, a threshold c/a ratio of about 1.045 was identified below which the electric field induced domain mobility increases sharply.

  13. Highly Efficient Lasing Action of Nd3+- and Cr3+-Doped Yttrium Aluminum Garnet Ceramics Based on Phonon-Assisted Cross-Relaxation Using Solar Light Source

    NASA Astrophysics Data System (ADS)

    Saiki, Taku; Nakatsuka, Masahiro; Imasaki, Kazuo

    2010-08-01

    We constructed a theory to explain the mechanism of laser generation with a high optical-optical conversion efficiency for Nd3+- and Cr3+-doped yttrium aluminum ceramics when sunlight or lamplight sources are used for pumping. As a result, a unique mechanism of laser action was found where the solar or lamp-light power could be converted to laser power with a high efficiency close to 80%, which has not previously been observed. The high conversion efficiency was not only considered to be based on one-to-one photon conversion but on two-photon excitation by a single photon with phonon assistance. Thus, the mechanism of lasing action should include a process where thermal energy is converted to photon energy. The theoretical results we obtained were consistent with those of the experiments.

  14. Dramatic influence of Dy3+ doping on strain and domain structure in lead-free piezoelectric 0.935(Na1/2Bi1/2)TiO3-0.065BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Li, C. Q.; Yao, Q. R.; Zhang, J. Z.; Hu, Z. G.; Wang, F. F.; Liu, A. Y.; Shi, W. Z.; Chu, J. H.

    2015-12-01

    An electric-field induced giant strain response and doping level dependent domain structural variations have been studied in the dysprosium (Dy3+)-modified 0.935(Na1/2Bi1/2)TiO3-0.065BaTiO3(xDy : NBBT) ceramics with the doping levels of 0%, 0.5%, 1%, and 2%. X-ray diffraction and Raman spectroscopy analyses not only demonstrates the change in ionic configurations induced by Dy3+ doping, but also shows the local crystal symmetry for x ≥ 0.5% doping levels to deviate from the idealized cubic structure. Piezoresponse force microscopy measurement exhibits the presence of an intermediate phase with orthorhombic symmetry at the critical Dy3+ doping level of 2%. Moreover, at this doping level, a giant recoverable nonlinear strain of ˜0.44% can be observed with high normalized strain (Smax/Emax) of 728 pm/V. At the same applied field, the strain exhibits a 175% increase than that of NBBT ceramic. Such a large strain stems from the varying coherence lengths of polar nanoregions (PNRs) and an unusual reversible 90° domain switching caused by the symmetry conforming property of point defects, where the restoring force is provided by unswitchable defects. The mechanism reveals a new possibility to achieve large electric-field strain effect for a wide range of ferroelectric systems, which can lead to applications in novel "on-off" actuators.

  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. 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

    2016-05-01

    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.

  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. 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. PMID:27100013

  19. 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

  20. 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.

  1. 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 ...

  2. 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

  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. Surface controlled reduction kinetics of nominally undoped polycrystalline CeO2.

    PubMed

    Knoblauch, Nicole; Dörrer, Lars; Fielitz, Peter; Schmücker, Martin; Borchardt, Günter

    2015-02-28

    Ceria is an interesting material for high temperature redox applications like solar-thermal splitting of CO2 and H2O. Technical implementation and reactor design for solar-thermal redox-based fuel generation requires reliable data for the chemical surface exchange coefficient and the chemical diffusivity of oxygen. The results of thermogravimetric relaxation experiments and equilibrium oxygen isotope exchange experiments with subsequent depth profiling analysis suggest that the reduction reaction of even dense samples of pure ceria (1 mm thickness, 93% of theoretical density) with a grain size of about 20 μm is surface reaction controlled. The chemical surface exchange coefficient exhibits a negative apparent activation energy (-64 kJ mol(-1)). This finding is corroborated by similar data from literature for the tracer surface exchange coefficient. The structure of the derived expression for the apparent activation energy further suggests that the chemical surface exchange coefficient should show only a very weak dependence on temperature for ceria doped with lower valence cations. PMID:25630597

  6. Rapid liquid phase sintered Mn doped BiFeO3 ceramics with enhanced polarization and weak magnetization

    NASA Astrophysics Data System (ADS)

    Kumar, Manoj; Yadav, K. L.

    2007-12-01

    Single-phase BiFe1-xMnxO3 multiferroic ceramics have been synthesized by rapid liquid phase sintering method to study the influence of Mn substitution on their crystal structure, dielectric, magnetic, and ferroelectric behaviors. From XRD analysis it is seen that Mn substitution does not affect the crystal structure of the BiFe1-xMnxO3 system. An enhancement in magnetization was observed for BiFe1-xMnxO3 ceramics. However, the ferooelectric hysteresis loops were not really saturated, we observed a spontaneous polarization of 10.23μC /cm2 under the applied field of 42kV/cm and remanent polarization of 3.99μC/cm2 for x =0.3 ceramic.

  7. FTIR and optical assessment of zinc doped calcium phospho-borosilicate sol-gel glasses/glass-ceramics

    NASA Astrophysics Data System (ADS)

    Kumar, V.; Arora, N.; Pandey, O. P.; Kaur, G.

    2015-08-01

    CaO-P2O5-ZnO-SiO2-B2O3 glasses with varying compositions of calcium oxide and phosphorous oxide are synthesized using sol-gel technique. The glasses are heat-treated for a duration of 10 h at 500°C to obtain the glass-ceramics. The glass-ceramics and glasses are characterized using Fourier transform infrared spectroscopy (FTIR) and UV-Visible spectroscopy. Extinction coefficients, attenuation coefficients and dielectric constant have been obtained for all the glasses as well as glass ceramics. The results are discussed in light of non-bridging oxygens (NBO) and heat-treatment of glasses. In addition to this, the effect of calcium and phosphorous on the infra-red spectra has been analysed thoroughly.

  8. 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.

  9. 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

    2016-04-01

    Lead-free ceramics (Ba0.85Ca0.15)(Zr0.9Ti0.1)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.

  10. 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.

  11. 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.

  12. Laser and optical properties of Yb:YAG ceramics with layered doping distribution: design, characterization and evaluation of different production processes

    NASA Astrophysics Data System (ADS)

    Toci, Guido; Lapucci, Antonio; Ciofini, Marco; Esposito, Laura; Hostaša, Jan; Gizzi, Leonida A.; Labate, Luca; Ferrara, Paolo; Pirri, Angela; Vannini, Matteo

    2016-03-01

    The laser, optical and spectroscopic properties of multilayer Yb:YAG ceramic structures, differently activated, were investigated. The structures were designed by means of Finite Element Modeling, adjusting the doping distributions to reduce peak temperature, surface deformation and thermally induced stresses, depending on the pump and cooling geometry. Two ceramic processes were used, i.e. dry pressing of spray-dried powders (SD) and tape casting (TC), resulting in different defect density and size distribution: TC gives a more uniform transmission, whereas SD results in larger, unevenly scattered defects. The spectroscopic properties were found independent from the production process. The laser performance has been characterized under high intensity pumping in a longitudinally diode pumped laser cavity, comparing the behavior of the different structures in terms of slope efficiency, stability under increasing thermal load, spatial uniformity of laser emission. Slope efficiency values as high as 58% in Quasi-CW pumping conditions and 54% in CW conditions was measured in two-layers structures. The production process and the number of layers influenced the behavior of the samples, in particular regarding the spatial uniformity of the laser emission. Samples made by tape casting have shown overall a better thermal stability with respect to the samples made by spray drying.

  13. 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.

  14. [Research on SCR denitrification of MnOx/Al2O3 modified by CeO2 and its mechanism at low temperature].

    PubMed

    Guo, Jing; Li, Cai-Ting; Lu, Pei; Cui, Hua-Fei; Peng, Dun-Liang; Wen, Qing-Bo

    2011-08-01

    The Al2O3,which has large specific surface area and is used as carrier,was prepared by sol-gel method in this study. Series catalysts of MnOx, CeO2 plus MnOx supported on Al2O3 by isometric impregnation method. The SCR denitrification experimental conditions were as follows: NH3 as reductive agent, certain gas velocity and suitable ratio of gas mixed was setup. Furthermore, the experiments of BET, XRD and SEM were also carried out respectively in order to obtain physicochemical properties of the prepared catalysts. The experimental results showed that the loading of active component and calcination temperature made a big difference to the catalysts' performance. With appropriate addition of CeO2, MnOx/Al2O3 exhibits better activity and stability. For MnOx/Al2O3, the catalytic activity on NO was greatly influenced by its loaded content, and 7% MnOx/Al2O3 showed superior catalytic activity among the MnOx/Al2O3. The addition of CeO2 could greatly improve the dispersibility of MnOx on the carrier and increase its catalytic activity. The 4% CeO2 addition was the optimum loaded mass precent. Forthermore, 550 degrees C is the best calcination temperature, as MnOx formed different crystalline phases with temperature, at the same time, the addition of CeO2 could affect MnOx crystalline phase. The catalytic mechanism of SCR on NO was also discussed. PMID:22619944

  15. Thick CeO2-TiO2 sol-gel coatings for Li-ion storage electrode in electrochromic devices

    NASA Astrophysics Data System (ADS)

    Choi, Kyo-Sook; Heusing, Sabine; Aegerter, Michel A.

    2002-10-01

    CeO2-TiO2 sol-gel coatings are well known as Li-ion storage electrode in electrochromic (EC) devices of the form glass/ TE /WO3/ electrolyte/ CeO2-TiO2/ TE/ glass (TE: transparent electrode, e.g. SnO2:F, FTO). The charge capacity of the CeO2-TiO2 coating is a limiting factor to get a high coloration intensity of such devices. In order to improve the charge capacity of these electrodes, new routes for the preparation of thick porous CeO2-TiO2 sol-gel layers were tested. One route was the preparation of thick porous TiO2 coatings on a conducting glass support (FTO) using a solution of colloidal TiO2 particles. After heat treatment at temperatures up to 550°C the coatings were soaked in a solution of a cerium-IV (Ce(NH4)2(NO3)6) or a cerium-III salt (Ce(NO3)3 6H2O) and heat treated again. Another route was the preparation of sols by mixing a solution of the cerium-IV or cerium-III salt or a colloidal CeO2-sol with the colloidal solution of TiO2. After dip coating on FTO-glass the coatings were also heat treated at temperatures up to 500°C. ALl these coatings were studied electrochemically in 1 M LiC1O4 in propylene carbonate electrolyte. Although thick porous single coatings could be obtained, typically 450 nm for TiO2 and 600 nm for cerium-titanium oxide, the intercalated and deintercalcated Li+ charges remain small and lie in the range of 2 mC/cm2 to 3 mC/cm2. The reasons for such low charge capacity is discussed.

  16. 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

  17. Improvement of ground granulated blast furnace slag on stabilization/solidification of simulated mercury-doped wastes in chemically bonded phosphate ceramics.

    PubMed

    Liu, Zhongzhe; Qian, Guangren; Zhou, Jizhi; Li, Chuanhua; Xu, Yunfeng; Qin, Zhe

    2008-08-30

    This paper investigated the effectiveness of (ground granulated blast furnace slag) GGBFS-added chemically bonded phosphate ceramic (CBPC) matrix on the stabilization/solidification (S/S) of mercury chloride and simulated mercury-bearing light bulbs (SMLB). The results showed that the maximal compressive strength was achieved when 15% and 10% ground GGBFS was added for HgCl(2)-doped and SMLB-doped CBPC matrices, respectively. The S/S performances of GGBFS-added matrices were significantly better than non-additive matrices. As pore size was reduced, the leaching concentration of Hg(2+) from GGBFS-added CBPC matrix could be reduced from 697 microg/L to about 3 microg/L when treating HgCl(2). Meanwhile, the main hydrating product of GGBFS-added matrices was still MgKPO(4).6H(2)O. The improvement of S/S effectiveness was mainly due to physical filling of fine GGBFS particles and microencapsulation of chemical cementing gel. PMID:18289781

  18. 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

  19. 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.

  20. 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.