Overall water splitting on (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution photocatalyst: relationship between physical properties and photocatalytic activity.

PubMed

Maeda, Kazuhiko; Teramura, Kentaro; Takata, Tsuyoshi; Hara, Michikazu; Saito, Nobuo; Toda, Kenji; Inoue, Yasunobu; Kobayashi, Hisayoshi; Domen, Kazunari

2005-11-03

The physical and photocatalytic properties of a novel solid solution between GaN and ZnO, (Ga(1-x)Zn(x))(N(1-x)O(x)), are investigated. Nitridation of a mixture of Ga(2)O(3) and ZnO at 1123 K for 5-30 h under NH(3) flow results in the formation of a (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution with x = 0.05-0.22. With increasing nitridation time, the zinc and oxygen concentrations decrease due to reduction of ZnO and volatilization of zinc, and the crystallinity and band gap energy of the product increase. The highest activity for overall water splitting is obtained for (Ga(1-x)Zn(x))(N(1-x)O(x)) with x = 0.12 after nitridation for 15 h. The crystallinity of the catalyst is also found to increase with increasing the ratio of ZnO to Ga(2)O(3) in the starting material, resulting in an increase in activity.

Coprecipitation of nickel zinc malonate: A facile and reproducible synthesis route for Ni{sub 1−x}Zn{sub x}O nanoparticles and Ni{sub 1−x}Zn{sub x}O/ZnO nanocomposites via pyrolysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lontio Fomekong, Roussin, E-mail: lonforou@yahoo.fr; Institut de la Matière Condensée et des Nanosciences, Université Catholique de Louvain, Croix du Sud 1, 1348 Louvain-La-Neuve; Kenfack Tsobnang, Patrice

2015-10-15

Nanoparticles of Ni{sub 1−x}Zn{sub x}O and Ni{sub 1−x}Zn{sub x}O/ZnO, which can be good candidates for selective gas sensors, were successfully obtained via a two-step synthetic route, in which the nickel zinc malonate precursor was first synthesized by co-precipitation from an aqueous solution, followed by pyrolysis in air at a relatively low temperature (~500 °C). The precursor was characterized by ICP-AES, FTIR and TG and the results indicate the molecular structure of the precursor to be compatible with Ni{sub 1−x}Zn{sub x}(OOCCH{sub 2}COO)·2H{sub 2}O. The decomposition product, characterized using various techniques (FTIR, XRD, ToF-SIMS, SEM, TEM and XPS), was established to bemore » a doped nickel oxide (Ni{sub 1−x}Zn{sub x}O for 0.01≤x≤0.1) and a composite material (Ni{sub 1−x}Zn{sub x}O/ZnO for 0.2≤x≤0.5). To elucidate the form in which the Zn is present in the NiO structure, three analytical techniques were employed: ToF-SIMS, XRD and XPS. While ToF SIMS provided a direct evidence of the presence of Zn in the NiO crystal structure, XRD showed that Zn actually substitutes Ni in the structure and XPS is a bit more specific by indicating that the Zn is present in the form of Zn{sup 2+} ions. - Highlights: • Coprecipitation synthesis of nickel zinc malonate single bath precursor was achieved. • The as synthesized precursors are an homogeneous mixture of nickel and zinc malonate. • XRD, ToF-SIMS, XPS, SEM and TEM was used to characterized decomposition products. • Ni{sub 1−x}Zn{sub x}O nanoparticles (0.01≤x≤0.1) formed after pyrolysis (~500 °C) of precursor. • Ni{sub 1−x}Zn{sub x}O/ZnO nanocomposite (0.2≤x≤0.5) formed after pyrolysis at 500 °C of precursor.« less

Low temperature magnetization and anomalous high temperature dielectric behaviour of (1-x) YMnO3/xZnFe2O4 composites

NASA Astrophysics Data System (ADS)

Kumar, Virendra; Gaur, Anurag

2018-04-01

We synthesized YMnO3 and ZnFe2O4 composites, (1-x)YMnO3/x(ZnFe2O4) with x = 0, 0.05, 0.10, and 0.15 by high temperature sintering. X-ray diffraction (XRD) patterns indicate the successful formation of composites. Weak ferromagnetism is manifested below Néel temperature (TN) for pristine YMnO3, according to (M-H) study performed at 10 K. For (1-x)YMnO3/xZnFe2O4 (x = 0.05, 0.10, 0.15) a thin coercivity is observed in all compositions, due to short range magnetic ordering at low temperature after the insertion of ZnFe2O4. For pristine YMnO3 explicit divarication between FC-ZFC curves is observed, with crimps observed in both FC and ZFC curves at 75 K, which is the TN of YMnO3. For 1-x(YMnO3)/x ZnFe2O4 composites (x = 0.05, 0.10, 0.15) crimps are perceived only in ZFC curves at slightly varying values of 39.8, 42.32 and 45.63 K respectively. Anomalous peaks are observed in high temperature dielectric curves above 400 K for 1-x(YMnO3)/xZnFe2O4 (x = 0, 0.05, 0.10, 0.15) composites due to Maxwell-Wagner relaxation effect.

Identification of NpO2+x in the binary Np-O system

NASA Astrophysics Data System (ADS)

Tayal, Akhil; Conradson, Steven D.; Baldinozzi, Gianguido; Namdeo, Sonu; Roberts, Kevin E.; Allen, Patrick G.; Shuh, David K.

2017-07-01

In contrast to UO2 and PuO2, there is no consensus on the existence of mixed valence NpO2+x, resulting in a gap between NpO2 and Np2O5 (the highest binary oxide of Np) in the Np-O phase diagram. We now show NpO2+x via Np LIII Extended X-ray Absorption Fine Structure (EXAFS) spectra of three samples of NpO2 that, analogous to U and Pu, exhibit multisite Np-O distributions with varying numbers of oxygen atoms at 1.87-1.91 Å. This is supported by the diffraction pattern of the sample with the largest amount of this oxo-type species that can be refined with both the simple fluorite structure and a trigonal one related to α-U4O9. The implied Np(V)-bridging oxo moieties as well as possible indications of OHbar found by detailed EXAFS analysis suggest that NpO2+x more closely resembles PuO2+x than UO2+x. An additional common characteristic suggested by the EXAFS and X-Ray Diffraction (XRD) is the phase separation into NpO2 and what would be previously unreported Np4O9(-δ), indicative of O clustering.

Thermophysical properties and oxygen transport in (Th x,Pu 1-x)O 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galvin, C. O. T.; Cooper, M. W. D.; Rushton, M. J. D.

Using Molecular Dynamics, this paper investigates the thermophysical properties and oxygen transport of (Th x,Pu 1–x)O 2 (0 ≤ x ≤ 1) between 300–3500 K. Specifically, the superionic transition is investigated and viewed via the thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure. Oxygen diffusivity and activation enthalpy are also investigated. Below the superionic temperature an increase of oxygen diffusivity for certain compositions of (Th x,Pu 1–x)O 2 compared to the pure end members is predicted. Oxygen defect formation enthalpies are also examined, as they underpin the superionic transition temperature and themore » increase in oxygen diffusivity. The increase in oxygen diffusivity for (Th x,Pu 1–x)O 2 is explained in terms of lower oxygen defect formation enthalpies for (Th x,Pu 1–x)O 2 than PuO 2 and ThO 2, while links are drawn between the superionic transition temperature and oxygen Frenkel disorder.« less

Thermophysical properties and oxygen transport in (Th x,Pu 1-x)O 2

DOE PAGES

Galvin, C. O. T.; Cooper, M. W. D.; Rushton, M. J. D.; ...

2016-10-31

Using Molecular Dynamics, this paper investigates the thermophysical properties and oxygen transport of (Th x,Pu 1–x)O 2 (0 ≤ x ≤ 1) between 300–3500 K. Specifically, the superionic transition is investigated and viewed via the thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure. Oxygen diffusivity and activation enthalpy are also investigated. Below the superionic temperature an increase of oxygen diffusivity for certain compositions of (Th x,Pu 1–x)O 2 compared to the pure end members is predicted. Oxygen defect formation enthalpies are also examined, as they underpin the superionic transition temperature and themore » increase in oxygen diffusivity. The increase in oxygen diffusivity for (Th x,Pu 1–x)O 2 is explained in terms of lower oxygen defect formation enthalpies for (Th x,Pu 1–x)O 2 than PuO 2 and ThO 2, while links are drawn between the superionic transition temperature and oxygen Frenkel disorder.« less

Enhancement of the physical properties of novel (1- x) NiFe2O4 + ( x) Al2O3 nanocomposite

NASA Astrophysics Data System (ADS)

Mansour, S. F.; Ahmed, M. A.; El-Dek, S. I.; Abdo, M. A.; Kora, H. H.

2017-07-01

NiFe2O4, Al2O3 and their nanocomposites; (1- x) NiFe2O4 + ( x) Al2O3, 0.0 ≤ x ≤ 1; were synthesized using the citrate-nitrate technique. The crystal structure was examined by X-ray diffraction, the microstructure was observed by transmission electron microscopy. The Curie temperature T C grows until reaching more than 1100 K with increasing alumina content ( x), while the saturation magnetization ( M s) decreased. The large improvement of room temperature resistivity which achieved two orders of magnitude from x = 0 to x = 70% was interpreted from the fact that the NiFe2O4 grains become electrically isolated and the conduction path is broken by the insulating Al2O3 nanoparticulates in the composite. The electrical properties of the nanocomposite could thus be tuned easily by adjusting the Al2O3 ratio to realize the targeted value of losses and resistivity at any temperature and frequency.

A molecular dynamics study of the atomic structure of (CaO)x(SiO2)1-x glasses.

PubMed

Mead, Robert N; Mountjoy, Gavin

2006-07-27

The local atomic environment of Ca in (CaO)x(SiO2)1-x glasses is of interest because of the role of Ca in soda-lime glass, the application of calcium silicate glasses as biomaterials, and the previous experimental measurement of the Ca-Ca correlation in CaSiO(3) glass. Molecular dynamics has been used to obtain models of (CaO)x(SiO2)1-x glasses with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5, and with approximately 1000 atoms and size approximately 25 A. As expected, the models contain a tetrahedral silica network, the connectivity of which decreases as x increases. In the glass-forming region, i.e., x = 0.4 and 0.5, Ca has a mixture of 6- and 7-fold coordination. Bridging oxygen makes an important contribution to the coordination of Ca, with most bridging oxygens coordinated to 2 Si plus 1 Ca. The x = 0.5 model is in reasonable agreement with previous experimental studies, and does not substantiate the previous theory of cation ordering, which predicted Ca arranged in sheets. In the phase-separated region, i.e., x = 0.1 and 0.2, there is marked clustering of Ca.

Ba{sub 3}ZnTa{sub 2-x}Nb{sub x}O{sub 9} and Ba{sub 3}MgTa{sub 2-x}Nb{sub x}O{sub 9} (0{<=}x{<=}1): synthesis, structure and dielectric properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thirumal, M.; Jawahar, I.N.; Surendiran, K.P.

2002-11-20

Oxides belonging to the families Ba{sub 3}ZnTa{sub 2-x}Nb{sub x}O{sub 9} and Ba{sub 3}MgTa{sub 2-x}Nb{sub x}O{sub 9} were synthesized by the solid state reaction route. Sintering temperatures of 1300 deg. C led to oxides with disordered (cubic) perovskite structure. However, on sintering at 1425 deg. C hexagonally ordered structures were obtained for Ba{sub 3}MgTa{sub 2-x}Nb{sub x}O{sub 9} over the entire range (0{<=}x{<=}1) of composition, while for Ba{sub 3}ZnTa{sub 2-x}Nb{sub x}O{sub 9} the ordered structure exists in a limited range (0{<=}x{<=}0.5). The dielectric constant is close to 30 for the Ba{sub 3}ZnTa{sub 2-x}Nb{sub x}O{sub 9} family of oxides while the Mg analoguesmore » have lower dielectric constant of {approx}18 in the range 50 Hz to 500 kHz. At microwave frequencies (5-7 GHz) dielectric constant increases with increase in niobium concentration (22-26) for Ba{sub 3}ZnTa{sub 2-x}Nb{sub x}O{sub 9}; for Ba{sub 3}MgTa{sub 2-x}Nb{sub x}O{sub 9} it varies between 12 and 14. The 'Zn' compounds have much higher quality factors and lower temperature coefficient of resonant frequency compared to the 'Mg' analogues.« less

Structural investigation of (111) oriented (BiFeO3)(1-x)Λ/(LaFeO3)xΛ superlattices by X-ray diffraction and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Belhadi, J.; Yousfi, S.; Bouyanfif, H.; El Marssi, M.

2018-04-01

(BiFeO3)(1-x)Λ/(LaFeO3)xΛ superlattices (SLs) with varying x have been grown by pulsed laser deposition on (111) oriented SrTiO3 substrates. In order to obtain good epitaxy and flat samples, a conducting SrRuO3 buffer has been deposited prior to the superlattices to screen the polar mismatch for such (111) SrTiO3 orientation. X-ray diffraction reciprocal space mapping on a different family of planes was collected and evidenced a room temperature structural change at x = 0.5 from a rhombohedral/monoclinic structure for rich BiFeO3 to an orthorhombic symmetry for rich LaFeO3. This symmetry change has been confirmed by Raman spectroscopy and demonstrates the different phase stability compared to similar SLs grown on (100) SrTiO3. The strongly anisotropic strain and oxygen octahedral rotation/tilt system compatibility at the interfaces probably explain the orientation dependence of the phase stability in such superlattices.

(Ba1- x Bi0.33 x Sr0.67 x )(Ti1- x Bi0.67 x V0.33 x )O3 and (Ba1- x Bi0.5 x Sr0.5 x )(Ti1- x Bi0.5 x Ti0.5 x )O3 solid solutions: phase evolution, microstructure, dielectric properties and impedance analysis

NASA Astrophysics Data System (ADS)

Chen, Xiuli; Li, Xiaoxia; Yan, Xiao; Liu, Gaofeng; Zhou, Huanfu

2018-06-01

Perovskite solid solution ceramics of (Ba1- x Bi0.33 x Sr0.67 x )(Ti1- x Bi0.67 x V0.33 x )O3 and (Ba1- x Bi0.5 x Sr0.5 x )(Ti1- x Bi0.5 x Ti0.5 x )O3 (BBSTBV, BBSTBT, 0.02 ≤ x ≤ 0.2) were prepared by the traditional solid state reaction technique. The phase evolution, microstructure and dielectric properties of BBSTBV and BBSTBT ceramics were researched. X-Ray diffraction results illustrated that both BBSTBV and BBSTBT could form a homogenous solid solution which has a similar structure with BaTiO3. The optimized properties of (Ba0.8Bi0.1Sr0.1)(Ti0.8Bi0.1Ti0.1)O3 ceramics with stable ɛ r ( 1769-2293), small Δ ɛ/ ɛ 25 °C values (± 15%) over a broad temperature range from - 58 to 151 °C and low tan δ ≤ 0.03 from - 11 to 131 °C were obtained. In the high-temperature region, the relaxation and conduction process are attributed to the thermal activation and the oxygen vacancies may be the ionic charge carriers in perovskite ferroelectrics.

Monoclinic Sr(1-x)Na(x)SiO(3-0.5x): new superior oxide ion electrolytes.

PubMed

Singh, Preetam; Goodenough, John B

2013-07-10

Oxide ion electrolytes determine the temperature of operation of solid oxide fuel cells, oxygen separation membranes, and oxygen sensors. There is a strong incentive to lower their operating temperatures, in a solid oxide fuel cell, for example, from Top > 800 °C to Top ≈ 500 °C. The use of low-cost Na(+) rather than K(+) as the dopant in monoclinic SrSiO3 (C12/C1) is shown to provide a larger solid solution range (0 < x ≤ 0.45) in Sr1-xNaxSiO3-0.5x and to achieve an oxide ion conductivity σo ≥ 10(-2) S·cm(-1) by 525 °C as a result of lowering the temperature of a smooth transition to full disorder of the mobile oxide ions. The Sr1-xNaxSiO3-0.5x electrolytes are much less hygroscopic than Sr1-xKxSiO3-0.5x and are stable with a nickel composite anode in 5% H2/Ar as well as with cathodes such as La1-xSrxMnO3-δ and Sr0.7Y0.3CoO3-δ in air, which makes them candidate electrolytes for intermediate-temperature solid oxide fuel cells or for other applications of oxide ion electrolytes.

Two-photon momentum density in La2-xSrxCuO4 and Nd2-xCexCuO4

NASA Astrophysics Data System (ADS)

Blandin, P.; Massidda, S.; Barbiellini, B.; Jarlborg, T.; Lerch, P.; Manuel, A. A.; Hoffmann, L.; Gauthier, M.; Sadowski, W.; Walker, E.; Peter, M.; Yu, Jaejun; Freeman, A. J.

1992-07-01

We present calculations of the electron-positron momentum density for the high-Tc superconductors La2-xSrxCuO4 and Nd2-xCexCuO4, together with experimental two-dimensional angular correlation of annihilation radiation (2D-ACAR) for Nd2-xCexCuO4. The calculations are based on first-principles electronic structure obtained using the full-potential linearized augmented-plane-wave and the linear muffin-tin orbital methods. Our results indicate a non-negligible overlap of the positron wave function with the CuO2 plane electrons responsible for the Fermi surfaces in these compounds. Therefore, these compounds may be well suited for investigating Fermi-surface-related effects. After the folding of umklapp terms according to Lock, Crisp, and West, the predicted Fermi-surface breaks are mixed with strong effects induced by the positron wave function in La2-xSrxCuO4, while their resolution is better in Nd2-xCexCuO4. A comparison of our calculations with the most recent experimental results for La2-xSrxCuO4 shows good agreement. For Nd2-xCexCuO4 good agreement is observed between theoretical and experimental 2D-ACAR profiles.

Preparation and study of (1 - x)CuFe2O4-xBaTiO3 (x = 0, 0.1 and 1) composite multiferroics

NASA Astrophysics Data System (ADS)

Murtaza, Tahir; Ali, Javid; Khan, M. S.

2018-07-01

The parent and mixed spinel-perovskite composite of (1 - x)CuFe2O4-xBaTiO3 (x = 0, 0.1 and 1) has been prepared by solid-state reaction method and studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, magnetometry and P-E lope tracer. The XRD results showed the formation of single phase tetragonal spinel CuFe2O4 and tetragonal perovskite BaTiO3 at room temperature, further XRD of composite 0.1CuFe2O4-0.9BaTiO3 reflects the two crystallographic phases with 1:9 ratio. The SEM micrographs show the homogeneous and uniform formation of the samples. Through EDAX analysis, the chemical composition of the sample is found to be same as the nominal composition. The high field Mossbauer data of CuFe2O4 sample shows the ferrimagnetic ordering in the sample. The observed M-H and P-E loops of the composite 0.1CuFe2O4-0.9BaTiO3 sample show the presence of spontaneous magnetization and spontaneous electric polarization indicating the multiferroic nature of the sample.

Dielectric Properties of BST/(Y 2O 3) x(ZrO 2) 1-x/BST Trilayer Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sahoo, Santosh K.; Misra, D.

2011-01-31

Thin films of Ba1-xSrxTiO3 (BST) are being actively investigated for applications in dynamic random access memories (DRAM) because of their properties such as high dielectric constant, low leakage current, and high dielectric breakdown strength. Various approaches have been used to improve the dielectric properties of BST thin films such as doping, graded compositions, and multilayer structures. We have found that inserting a ZrO2 layer in between two BST layers results in a significant reduction in dielectric constant as well as dielectric loss. In this work the effect of Y2O3 doped ZrO2 on the dielectric properties of BST/ZrO2/BST trilayer structure ismore » studied. The structure Ba0.8Sr0.2TiO3/(Y2O3)x(ZrO2)1-x/Ba0.8Sr0.2TiO3 is deposited by a sol-gel process on platinized Si substrate. The composition (x) of the middle layer is varied while keeping the total thickness of the trilayer film constant. The dielectric constant of the multilayer film decreases with the increase of Y2O3 amount in the film whereas there is a slight variation in dielectric loss. In Y2O3 doped multilayer thin films, the dielectric loss is lower in comparison to other films and also there is good frequency stability in the loss in the measured frequency range and hence very suitable for microwave device applications.« less

The photocatalytic properties of hollow (GaN)1-x(ZnO)x composite nanofibers synthesized by electrospinning

NASA Astrophysics Data System (ADS)

Wang, Ding; Zhang, Minglu; Zhuang, Huaijuan; Chen, Xu; Wang, Xianying; Zheng, Xuejun; Yang, Junhe

2017-02-01

(GaN)1-x(ZnO)x composite nanofibers with hollow structure were prepared by initial electrospinning, and the subsequent calcination and nitridation. The structure and morphology characteristics of samples were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The characterization results showed the phase transition from ZnGa2O4 to (GaN)1-x(ZnO)x solid-solution under ammonia atmosphere. The preparation conditions were explored and the optimum nitridation temperature and holding time are 750 °C and 2 h, respectively. The photocatalytic properties of (GaN)1-x(ZnO)x with different Ga:Zn atomic ratios were investigated by degrading Rhodamine B under the visible light irradiation. The photocatalytic activity sequence is (GaN)1-x(ZnO)x (Ga:Zn = 1:2) > (GaN)1-x(ZnO)x (Ga:Zn = 1:3) > ZnO nanofibers > (GaN)1-x(ZnO)x (Ga:Zn = 1:4) > (GaN)1-x(ZnO)x (Ga:Zn = 1:1). The photocatalytic mechanism of the (GaN)1-x(ZnO)x hollow nanofibers was further studied by UV-vis diffuse reflectance spectra. The excellent photocatalytic performance of (GaN)1-x(ZnO)x hollow nanofibers was attributed to the narrow band gap and high surface area of porous nanofibers with hollow structure.

Structural and magnetic properties of nanostructured composites (SrFe12O19)x(CaCu3Ti4O12)1-x

NASA Astrophysics Data System (ADS)

Gavrilova, T. P.; Deeva, J. A.; Yatsyk, I. V.; Yagfarova, A. R.; Gilmutdinov, I. F.; Lyadov, N. M.; Milovich, F. O.; Chupakhina, T. I.; Eremina, R. M.

2018-05-01

(SrFe12O19)x(CaCu3Ti4O12)1-x (x = 0.01, 0.03, 0.07, 0.1) composites were synthesized using a solid state method, while the pre-synthesized strontium hexaferrite SrFe12O19 (SFO) was added to the stoichiometric amount of CaO, CuO and TiO oxides to form the CaCu3Ti4O12 (CCTO) structure around SFO microinclusions. The structural and microstructural properties of obtained composites were studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. The magnetic properties were studied by electron spin resonance and magnetometry methods. Based on all experimental data we can conclude, that SFOxCCTO1-x nanostructured composites were formed only for concentrations x = 0.03 and x = 0.07, where SFO nanoinclusions are inside CCTO matrix, that leads to the strong mutual influence of the magnetic properties of both component.

Composition dependence of superconductivity in YBa2(Cu(3-x)Al(x))O(y)

NASA Technical Reports Server (NTRS)

Bansal, N. P.

1993-01-01

Eleven different compositions in the system YBa2(Cu(3-x)Al(x))O(y) (x = 0 to 0.3) have been synthesized and characterized by electrical resistivity measurements, powder X-ray diffraction, and scanning electron microscopy. The superconducting transition temperature T sub c (onset) was almost unaffected by the presence of alumina due to its limited solubility in YBa2Cu3O(7-x). However, T sub c(R = 0) gradually decreased, and the resistive tails became longer with increasing Al2O3 concentration. This was probably due to formation of BaAl2O4 and other impurity phases from chemical decomposition of the superconducting phase by reaction with Al2O3.

Heteroepitaxial growth of Ba1 - xSrxTiO3/YBa2Cu3O7 - x by plasma-enhanced metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Chern, C. S.; Liang, S.; Shi, Z. Q.; Yoon, S.; Safari, A.; Lu, P.; Kear, B. H.; Goodreau, B. H.; Marks, T. J.; Hou, S. Y.

1994-06-01

Epitaxial Ba1-xSrxTiO3(BST)/YBa2Cu3O7-x heterostructures with superior electrical and dielectric properties have been fabricated by plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD). Data of x-ray diffraction and high resolution transmission electron microscopy showed that <100> oriented Ba1-xSrxTiO3 layers were epitaxially deposited on epitaxial (001) YBa2Cu3O7-x layers. The leakage current density through the Ba1-xSrxTiO3 films was about 10-7 A/cm2 at 2 V (about 2×105 V/cm) operation. Moreover, the results of capacitance-temperature measurements showed that the PE-MOCVD Ba1-xSrxTiO3 films had Curie temperatures of about 30 °C and a peak dielectric constant of 600 at zero bias voltage. The Rutherford backscattering spectrometry and x-ray diffraction results showed that the BST film composition was controlled between Ba0.75Sr0.25TiO3 and Ba0.8Sr0.2TiO3. The structural and electrical properties of the Ba1-xSrxTiO3/YBa2Cu3O7-x heterostructure indicated that conductive oxide materials with close lattice to Ba1-xSrxTiO3 can be good candidates for the bottom electrode.

Oxidation and reduction behaviors of a prototypic MgO-PuO2-x inert matrix fuel

NASA Astrophysics Data System (ADS)

Miwa, Shuhei; Osaka, Masahiko

2017-04-01

Oxidation and reduction behaviors of prototypic MgO-based inert matrix fuels (IMFs) containing PuO2-x were experimentally investigated by means of thermogravimetry. The oxidation and reduction kinetics of the MgO-PuO2-x specimen were determined. The oxidation and reduction rates of the MgO-PuO2-x were found to be low compared with those of PuO2-x. It is note that the changes in O/Pu ratios of MgO-PuO2-x from stoichiometry were smaller than those of PuO2-x at high oxygen partial pressure.

Synthesis of SiO(x) powder using DC arc plasma.

PubMed

Jung, Chan-Ok; Park, Dong-Wha

2013-02-01

SiO(x) was prepared by DC arc plasma and applied to the anode material of lithium ion batteries. A pellet of a mixture of Si and SiO2 was used as the raw material. The ratios of the silicon and silicon dioxide (SiO2) mixtures were varied by controlling the Si-SiO2 molar ratio (Si-SiO2 = 1-4). Hydrogen gas was used as the reduction atmosphere in the chamber. The prepared SiO(x) was collected on the chamber wall. The obtained SiO(x) was characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD and TEM showed that the phase composition of the prepared particles was composed of amorphous SiO(x) and crystalline Si. The prepared SiO(x) showed wire and spherical morphology. XPS indicated the bonding state and 'x' value of the prepared SiO(x), which was close to one. The result of prepared SiO(x) is discussed from thermodynamic equilibrium calculations. The electrochemical behavior of the silicon monoxide anode was investigated.

Non-switching to switching transferring mechanism investigation for Ag/SiO x /p-Si structure with SiO x deposited by HWCVD

NASA Astrophysics Data System (ADS)

Liu, Yanhong; Wang, Ruoying; Li, Zhongyue; Wang, Song; Huang, Yang; Peng, Wei

2018-04-01

We proposed and fabricated an Ag/SiO x /p-Si sandwich structure, in which amorphous SiO x films were deposited through hot wire chemical vapor deposition (HWCVD) using tetraethylorthosilicate (TEOS) as Si and O precursor. Experimental results indicate that the I–V properties of this structure transfer from non-switching to switching operation as the SiO x deposition temperature increased. The device with SiO x deposited at high deposition temperature exhibits typical bipolar switching properties, which can be potentially used in resistive switching random accessible memory (RRAM). The transferring mechanism from non-switching to switching can be ascribed to the change of structural and electronic properties of SiO x active layer deposited at different temperatures, as evidenced by analyzing FTIR spectrum and fitting its I–V characteristics curves. This work demonstrates a safe and practicable low-temperature device-grade SiO x film deposition technology by conducting HWCVD from TEOS.

Characterization of ZrO2 and (ZrO2)x(Al2O3)1-X thin films on Si substrates: effect of the Al2O3 component

NASA Astrophysics Data System (ADS)

Vitanov, P.; Harizanova, A.; Ivanova, T.

2014-05-01

ZrO2 and (ZrO2)x(Al2O3)1-x films were deposited by the sol-gel technique on Si substrates. The effect of the Al2O3 additive on the film surface morphology was studied by atomic force microscopy (AFM). The mixed oxide films showed a smoother morphology and lower values of the root-mean-square (RMS) roughness compared to ZrO2. Further, FTIR spectra indicated that ZrO2 underwent crystallization. The electrical measurements of the MIS structure revealed that the presence of Al2O3 and the amorphization affects its dielectric properties. The MIS structure with (ZrO2)x(Al2O3)1-x showed a lower fixed charge (~ 6×1010 cm-2) and an interface state density in the middle of the band gap of 6×1011 eV-1 cm-2). The dielectric constant measured was 22, with the leakage current density decreasing to 2×10-8 A cm-2 at 1×106 V cm-1.

Perovskite-Type Oxides. I. Structural, Magnetic, and Morphological Properties of LaMn 1- xCu xO 3 and LaCo 1- xCu xO 3 Solid Solutions with Large Surface Area

NASA Astrophysics Data System (ADS)

Porta, Piero; De Rossi, Sergio; Faticanti, Marco; Minelli, Giuliano; Pettiti, Ida; Lisi, Luciana; Turco, Maria

1999-09-01

Perovskite-type compounds of general formula LaMn1-xCuxO3 and LaCo1-xCuxO3 (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared by calcining the citrate gel precursors at 823, 923, and 1073 K. The decomposition of the precursors was followed by thermal analysis and the oxides were investigated by means of elemental analysis (atomic absorption and redox titration), X-ray powder diffraction, BET surface area, X-ray absorption (EXAFS and XANES), electron microscopy (SEM and TEM), and magnetic susceptibility. LaMn1-xCuxO3 samples are perovskite-like single phases up to x=0.6. At x=0.8 CuO and La2CuO4 phases are present in addition to perovskite. For x=1.0 the material is formed by CuO and La2CuO4. Mn(IV) was found by redox titration in all Mn-based perovskite samples, its fraction increasing with the increase in copper content. EXAFS and XANES analyses confirmed the presence of Mn(IV). Cation vacancies in equal amounts in the 12-coordinated A and octahedral B sites are suggested in the samples with x=0.0 and x=0.2, while for x=0.6 anionic vacancies are present. Materials with sufficiently high surface area (22-36 m2 g-1 for samples fired at 923 K and 14-22 m2 g-1 for those fired at 1073 K) were obtained. Crystallite sizes in the ranges 390-500 and 590-940 Å for samples calcined at 923 and 1073 K, respectively, were determined from the FWHM of the (102) X-ray diffraction peak. TEM patterns of LaMnO3 showed almost regular hexagonal prismatic crystals with sizes of the same order of magnitude (800 Å) of those drawn from X-ray diffraction, while no evidence of defect clustering was drawn out from TEM and electron diffraction images. For the sample with x=0.6, TEM and electron diffraction patterns revealed perturbation of the structure. Magnetic susceptibility studies show a ferromagnetic behavior that decreases with increase in x. LaCo1-xCuxO3 samples are perovskite-like single phases up to x=0.2. For x=0.4 a small amount of La2CuO4, in addition to perovskite, is detected. For

Positron annihilation study of Y 1- xPr xBa 2Cu 3O 7

NASA Astrophysics Data System (ADS)

Zhao, Y. G.; Cao, B. S.; Yu, W. Z.; Du, Z. H.; Wang, Y. J.; Luo, C. Y.; Hu, H.; Wang, S.; Yang, J. H.; He, A. S.; Gu, B. L.

1995-02-01

A positron annihilation study of Y 1- xPr xBa 2Cu 3O 7 was performed. The results showed that charge transfer between the CuO 2 planes and 1D CuO chains upon Pr doping, as proposed in the literature, did not occur. Pr doping suppressed the anomaly of positron annihilation lifetime near and below Tc which has been observed in YBa 2Cu 3O 7. The perfection of the 1D CuO chains was reduced by Pr doping and this may be partly responsible for the increase of resistivity with Pr doping, and finally the semiconducting behaviour of DC resistivity in Y 1- xPr xBa 2Cu 3O 7 with x > 0.6.

Investigations on the local structures of Cu2+ at various BaO concentrations in 59B2O3-10K2O-(30-x)ZnO-xBaO-1CuO glasses

NASA Astrophysics Data System (ADS)

Jin, Jia-Rui; Wu, Shao-Yi; Hong, Jian; Liu, Shi-Nan; Song, Min-Xian; Teng, Bao-Hua; Wu, Ming-He

2017-11-01

The local structures and electron paramagnetic resonance (EPR) parameters for Cu2+ in 59B2O3-10K2O-(30-x)ZnO-xBaO-1CuO (BKZBC) glasses are theoretically investigated with distinct modifier BaO concentrations x (= 0, 6, 12, 18, 24 and 30 mol %). The ? clusters are found to undergo the relative tetragonal elongations of about 13.5 and 5.0% at zero and higher BaO concentrations. The concentration dependences of the measured d-d transition bands, g factors and A// are suitably reproduced from the Fourier type functions or sign functions of the relevant quantities with x by using only six adjustable parameters. The features of the EPR parameters and the local structures of Cu2+ are analysed in a consistent way by considering the differences in the local ligand field strength and electronic cloud admixtures around Cu2+ under addition of Ba2+ with the highest ionicity and polarisability. The present theoretical studies would be helpful to the researches on the structures, optical and EPR properties for the similar potassium barium zinc borate glasses containing copper with variation concentration of modifier BaO.

Lead-Free KNbO3:xZnO Composite Ceramics.

PubMed

Lv, Xiang; Li, Zhuoyun; Wu, Jiagang; Xiao, Dingquan; Zhu, Jianguo

2016-11-09

It is a tough issue to develop dense and water resistant KNbO 3 ceramics due to high evaporation and hygroscopicity of K 2 O. Here, KNbO 3 :xZnO composite ceramics were used to successfully solve this problem, where ZnO particles were randomly distributed into a KNbO 3 matrix. The addition of ZnO hardly affects the phase structure of KNbO 3 , and moreover, the enhancement of electrical properties, thermal stability, and aging characteristics was observed in KNbO 3 :xZnO composite ceramics. The composites possessed the maximum d 33 of 120 ± 5 pC/N, which is superior to that of pure KNbO 3 (d 33 = 80 pC/N). More importantly, a strong water resistance and an aging-free characteristic were observed in KNbO 3 :0.4ZnO. This is the first time for KNbO 3 ceramics to simultaneously improve electrical properties and resolve the water-absorbing properties. We believe that these composite ceramics are promising for practical applications.

Efficiency enhancement using a Zn1- x Ge x -O thin film as an n-type window layer in Cu2O-based heterojunction solar cells

NASA Astrophysics Data System (ADS)

Minami, Tadatsugu; Nishi, Yuki; Miyata, Toshihiro

2016-05-01

Efficiency enhancement was achieved in Cu2O-based heterojunction solar cells fabricated with a zinc-germanium-oxide (Zn1- x Ge x -O) thin film as the n-type window layer and a p-type Na-doped Cu2O (Cu2O:Na) sheet prepared by thermally oxidizing Cu sheets. The Ge content (x) dependence of the obtained photovoltaic properties of the heterojunction solar cells is mainly explained by the conduction band discontinuity that results from the electron affinity difference between Zn1- x Ge x -O and Cu2O:Na. The optimal value of x in Zn1- x Ge x -O thin films prepared by pulsed laser deposition was observed to be 0.62. An efficiency of 8.1% was obtained in a MgF2/Al-doped ZnO/Zn0.38Ge0.62-O/Cu2O:Na heterojunction solar cell.

Nanocrystalline Ce1- x La x O2- δ Solid Solutions Synthesized by Hydrolyzing and Oxidizing

NASA Astrophysics Data System (ADS)

Hou, Xueling; Xue, Yun; Han, Ning; Lu, Qianqian; Wang, Xiaochen; Phan, Manh-Huong; Zhong, Yunbo

2016-05-01

We undertook a novel batch production approach for the synthesis of CeO2 nanopowders doped with rare earth elements. Solid solution nanopowders of Ce1- x La x O2- δ ( x = 0.15) were successfully synthesized in a large-scale and low-cost production by hydrolyzing and oxidizing Ce-La-C alloys at room temperature and subsequent calcining of their powders at different temperatures (873-1073 K) for 1 h. The Ce-La-C alloys were prepared in a vacuum induction melting furnace. The final products were characterized by x-ray diffraction, transmission electron microscopy, Brunner-Emmet-Teller (BET) surface area analyzer, and Raman spectroscopy. The calculated lattice parameters of the cubic fluorite-type phase of CeO2 tended to increase when La3+ was incorporated into CeO2. The F 2g band shift and the absence of a peak corresponding to La2O3 in the Raman spectra consistently confirmed the incorporation of the La3+ ion into CeO2, and the formation of Ce1- x La x O2- δ solid solutions as manifested by increased oxygen vacancy defects. High-quality Ce1- x La x O2- δ nanopowders of ~10-15 nm diameter with a high BET surface area of ~77 m2 g-1 were obtained. The average crystallite size of Ce1- x La x O2- δ was found to be smaller than that of CeO2 for the same calcination temperature of 1073 K, demonstrating that the introduction of La3+ into CeO2 can stabilize the host lattice and refine the grain size at high temperatures.

Terahertz dielectric response of ferroelectric Ba(x)Sr(1-x)TiO3 thin films.

PubMed

Kang, Seung Beom; Kwak, Min Hwan; Choi, Muhan; Kim, Sungil; Kim, Taeyong; Cha, Eun Jong; Kang, Kwang Yong

2011-11-01

Terahertz time-domain spectroscopy has been used to investigate the dielectric and optical properties of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films for nominal x-values of 0.4, 0.6, and 0.8 in the frequency range of 0.3 to 2.5 THz. The ferroelectric thin films were deposited at approximately 700 nm thickness on [001] MgO substrate by pulsed laser deposition. The measured complex dielectric and optical constants were compared with the Cole-Cole relaxation model. The results show that the Cole-Cole relaxation model fits well with the data throughout the frequency range and the dielectric relaxation behavior of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films varies with the films compositions. Among the compositions of Ba(x)Sr(1-x)TiO(3) films with different Ba/Sr ratios, Ba(0.6)Sr(0.4)TiO(3) has the highest dielectric constants and the shortest dielectric relaxation time.

Effect of the Ti/Si ratio of spin coating solutions on surface passivation of crystalline silicon by TiO x -SiO x composite films

NASA Astrophysics Data System (ADS)

Yoshiba, Shuhei; Tanitsu, Katsuya; Suda, Yoshiyuki; Kamisako, Koichi

2017-06-01

Passivation films or antireflection coatings are generally prepared using costly vacuum or high-temperature processes. Thus, we report the preparation of TiO x -SiO x composite films by novel spin coatable solutions for the synthesis of low-cost passivation coating materials. The desired films were formed by varying the mixing ratios of TiO x and SiO x , and the resulting films exhibited excellent surface passivation properties. For the p-type wafer, an optimal effective surface recombination velocity (S eff) of 93 cm/s was achieved at \\text{TiO}x:\\text{SiO}x = 6:4, while a surface recombination current density (J 0s) of 195 fA/cm2 was obtained. In contrast, for the n-type wafer, an S eff of 27 cm/s and a J 0s of 38 fA/cm2 were achieved at \\text{TiO}x:\\text{SiO}x = 8:2. This excellent surface passivation effect could be attributed to the low interface state density and high positive fixed charge density. Furthermore, the thickness of the interfacial SiO x layer was determined to be important for obtaining the desired surface passivation effect.

EPR spectroscopic investigations in 15BaO-25Li2O-(60-x) B2O3-xFe2O3 glass system

NASA Astrophysics Data System (ADS)

Bhogi, Ashok; Kumar, R. Vijaya; Kistaiah, P.

2018-05-01

Glasses with composition 15BaO-25Li2O-(60-x) B2O3 -xFe2O3 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1 mol %) were prepared by the conventional melt quenching technique. These glasses were characterized using X-ray diffraction (XRD). Electron paramagnetic resonance (EPR) investigations have been carried out as a function of iron ion concentration. The observed EPR spectra of Fe3+ ion exhibits resonance signals at g= 2.0, 4.3 and 8.0. The resonance signal at g= 4.3 is due to isolated Fe3+ ions in site with rhombic symmetry where as the g= 2.0 resonance signal is attributed to the Fe3+ ions coupled by exchange interaction in a distorted octahedral environment and the signal at g= 8.0 arises from axially distorted sites. The number of spins participating in resonance (N) and its paramagnetic susceptibilities (χ) have also been evaluated. The peak-to-peak line width ΔB for the resonance lines at g ≈ 4.3 and at g ≈ 2.0 is increasing as function of the iron ion content. The line intensity of the resonance centered at g ≈ 4.3 and at g ≈ 2.0 increases up to 0.8 mol% of Fe2O3 and for 1 mol% of Fe2O3 its value is found to decrease. The analysis of these results indicated that the conversion some of Fe3+ cations to Fe2+ ions beyond 0.8 mol%.

Thermodynamic properties of Ba{sub 1-x}La{sub x}CoO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaur, N. K., E-mail: srl-nkgaur@yahoo.co.in; Thakur, Rasna, E-mail: rasnathakur@yahoo.com; Thakur, Rajesh K., E-mail: thakur.rajesh2009@gmail.com

2016-05-06

We have predicted the thermodynamic behavior of Ba{sub 1-x}La{sub x}CoO{sub 3} family at temperature 1K≤T≤300K using the Modified Rigid Ion Model (MRIM). The specific heat of BaCoO{sub 3} with La doping in the perovskite structure at A-site has been reported. Also, the cohesive energy (ϕ), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θ{sub D}), specific heat (C) and Gruneisen parameter (γ) of Ba{sub 1-x}La{sub x}CoO{sub 3} compounds are discussed.

Thermoelectric transport properties of Ca3Co4- x Ni x O9+ δ oxide materials

NASA Astrophysics Data System (ADS)

Park, K.; Cha, J. S.; Nam, S. W.; Choi, S.-M.; Seo, W.-S.; Lee, S.; Lim, Y. S.

2016-01-01

Nano-sized Ca3Co4- x Ni x O9+ δ (0 ≤ x ≤ 0.3) thermoelectric powders are synthesized by using the solution combustion method, with aspartic acid as a combustion fuel. The synthesized Ca3Co4- x Ni x O9+ δ nano-sized powders exhibit a spherical-like shape and a smooth surface. Higher Ni content results in a smaller grain size and a higher porosity, resulting in a decrease in the electrical conductivity. However, the Seebeck coefficient of Ni-added Ca3Co4O9 is much higher than that of Ca3Co4O9. The highest power factor (1.4 × 10-4 Wm-1K-2), which is more than nine times larger than that of Ca3Co4O9, is attained for Ca3Co0.38Ni0.2O9+ δ at 800 °C. The addition of a small amount of Ni is highly effective in improving the thermoelectric properties of Ca3Co4O9. We believe that Ca3Co4- x Ni x O9+ δ is a potential p-type thermoelectric material for renewable energy conversion.

High performance binder-free SiO x/C composite LIB electrode made of SiO x and lignin

DOE PAGES

Chen, Tao; Hu, Jiazhi; Zhang, Long; ...

2017-07-19

A high performance binder-free SiO x/C composite electrode was synthesized by mixing SiO x particles and Kraft lignin in a cryo-mill followed by heat treatment at 600 °C. After the heat treatment, lignin formed a conductive matrix hosting SiO x particles, ensuring electronic conductivity, connectivity, and accommodation of volume changes during lithiation/delithiation. As the result, no conventional binder or conductive agent was necessary. When electrochemically cycled, the composite electrode delivered excellent performance, maintaining ~900 mAh g -1 after 250 cycles at a rate of 200 mA g -1, and good rate capability. The robustness of the electrode was also examinedmore » by post-cycling SEM images, where few cracks were observed. The excellent electrochemical performance can be attributed to the comparatively small volume change of SiO x-based electrodes (160%) and the flexibility of the lignin derived carbon matrix to accommodate the volume change. In conclusion, this work should stimulate further interests in using bio-renewable resources in making advanced electrochemical energy storage systems.« less

High performance binder-free SiO x/C composite LIB electrode made of SiO x and lignin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Tao; Hu, Jiazhi; Zhang, Long

A high performance binder-free SiO x/C composite electrode was synthesized by mixing SiO x particles and Kraft lignin in a cryo-mill followed by heat treatment at 600 °C. After the heat treatment, lignin formed a conductive matrix hosting SiO x particles, ensuring electronic conductivity, connectivity, and accommodation of volume changes during lithiation/delithiation. As the result, no conventional binder or conductive agent was necessary. When electrochemically cycled, the composite electrode delivered excellent performance, maintaining ~900 mAh g -1 after 250 cycles at a rate of 200 mA g -1, and good rate capability. The robustness of the electrode was also examinedmore » by post-cycling SEM images, where few cracks were observed. The excellent electrochemical performance can be attributed to the comparatively small volume change of SiO x-based electrodes (160%) and the flexibility of the lignin derived carbon matrix to accommodate the volume change. In conclusion, this work should stimulate further interests in using bio-renewable resources in making advanced electrochemical energy storage systems.« less

Experimental and numerical study on transverse piezoelectricity of xBiInO3-(1 - x)PbTiO3 films by multilayer cantilevers

NASA Astrophysics Data System (ADS)

Sun, Ke-xue; Zhang, Shu-yi; Shui, Xiu-ji; Wasa, Kiyotaka

2018-02-01

The effective transverse piezoelectric coefficient of the piezoelectric films xBiInO3-(1 - x)PbTiO3 (x = 0,0.10,0.15,0.20) were studied experimentally and numerically by multilayer cantilevers. The xBiInO3-(1 - x)PbTiO3 thin films were deposited on (101)SrRuO3/(100)Pt/(100)MgO substrates and then covered with Pt electrode by RF-magnetron sputtering method. In experiments, the tip vibration amplitudes of the cantilevers for different x of the films were measured, in which the optimized compositions for maximizing the tip vibration can be found. Meanwhile, based on the bending model of multilayer piezoelectric cantilevers, the tip-deflection and transverse piezoelectricity of the cantilevers were simulated by COMSOL software. By comparing the experimental and numerical results, both are in agreement very well, and the mechanism of the optimized transverse piezoelectricity of the cantilevers was proposed finally.

First principles studies on the redox ability of (Ga(1-x)Zn(x))N(1-x)O(x) solid solutions and thermal reactions for H2 and O2 production on their surfaces.

PubMed

Du, Yaojun A; Chen, Yun-Wen; Kuo, Jer-Lai

2013-12-07

The (Ga1-xZnx)N1-xOx solid solution has been emerging as an effective photocatalyst for water splitting utilizing the visible solar spectrum, regarded as a host GaN bulk doped with ZnO impurities. H2 and O2 production occur simultaneously and stoichiometrically on the surface of (Ga1-xZnx)N1-xOx particles. In this work, we characterize the redox ability of (Ga1-xZnx)N1-xOx and find that a solid solution with a ZnO concentration of 0.125 < x < 0.250 is optimal for water splitting. This is consistent with the experimental finding that the maximum photocatalytic activity of (Ga1-xZnx)N1-xOx is achieved at x = 0.13. The thermal reactions of water splitting are modeled on both the GaN and an idealized (Ga1-xZnx)N1-xOx (101[combining macron]0) surface. The computed activation barriers allow us to gain some clues on the efficiency of water splitting on a specific photocatalyst surface. Our results suggest that the non-polar (101[combining macron]0) and polar (0001) surfaces may play different roles in water splitting, i.e., the (101[combining macron]0) surface is responsible for O2 production, while hydroxyl groups could dissociate on the (0001) surface.

Origin of giant dielectric permittivity and weak ferromagnetic behavior in (1-x)LaFeO3-xBaTiO3 (0.0 ≤ x ≤ 0.25) solid solutions

NASA Astrophysics Data System (ADS)

Sreenivasu, T.; Tirupathi, P.; Prabahar, K.; Suryanarayana, B.; Chandra Mouli, K.

The solid solutions of (1-x) LaFeO3-xBaTiO3 (0.0≤x≤0.25) have been synthesized successfully by the conventional solid-state reaction method. Room temperature (RT) X-ray diffraction studies reveal the stabilization of orthorhombic phase with Pbnm space group. Complete solubility in the perovskite series was demonstrated up to x=0.25. The dielectric permittivity shows colossal dielectric constant (CDC) at RT. The doping of BaTiO3 in LaFeO3 exhibit pronounced CDC up to a composition x=0.15, further it starts to decrease. The frequency-dependent dielectric loss exhibits polaronic conduction, which can attribute to presence of multiple valence of iron. The relaxation frequency and polaronic conduction mechanism was shifted towards RT as function of x. Moreover, large magnetic moment with weak ferromagnetic behavior is observed in doped LaFeO3 solid solution, which might be the destruction of spin cycloid structure due to insertion of Ti in Fe-O-Fe network of LaFeO3.

Magnetic properties of Zn1-xNixO

NASA Astrophysics Data System (ADS)

Mondal, A.; Giri, N.; Sarkar, S.; Ray, Ruma

2018-05-01

Ni doped ZnO (Zn1-xNixO for 0.01 ≤ x ≤ 0.11) have been prepared by chemical precipitation method. X-ray diffraction corroborates a hexagonal wurzite structure without any impurity phases upto 11% Ni doping. Morphology of the particles is investigated by FE-SEM which exhibits either rod or tube like structure depending on the dopant concentration. Magnetization of Zn1-xNixO for 0.03 ≤ x ≤ 0.11 measured at room temperature infers the paramagnetic behavior. Zero field cooled and field cooled magnetization for x = 0.11 follows Curie-Weiss behavior above 122 K with effective paramagnetic moment 3.9μB. The non-linear magnetic hysteresis loop at 2 K with a small coercivity (300 Oe) indicates signature of ferromagnetic ordering.

A Rutile Chevron Modulation in Delafossite-Like Ga 3–x In 3 Ti x O 9+x/2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rickert, Karl; Boullay, Philippe; Malo, Sylvie

2016-05-02

The structure solution of the modulated, delafossite-related, orthorhombic Ga 3–xIn 3Ti xO 9+x/2 for x = 1.5 is reported here in conjunction with a model describing the modulation as a function of x for the entire system. Previously reported structures in the related A 3–xIn 3Ti xO 9+x/2 (A = Al, Cr, or Fe) systems use X-ray diffraction to determine that the anion lattice is the source of modulation. Neutron diffraction, with its enhanced sensitivity to light atoms, offers a route to solving the modulation and is used here, in combination with precession electron diffraction tomography (PEDT), to solve themore » structure of Ga 1.5In 3Ti 1.5O 9.75. We construct a model that describes the anion modulation through the formation of rutile chevrons as a function of x. This model accommodates the orthorhombic phase (1.5 ≤ x ≤ 2.1) in the Ga 3-xIn 3Ti xO 9+x/2 system, which transitions to a biphasic mixture (2.2 ≤ x ≤ 2.3) with a monoclinic, delafossite-related phase (2.4 ≤ x ≤ 2.5). The optical band gaps of this system are determined, and are stable at ~3.4 eV before a ~0.4 eV decrease between x = 1.9 and 2.0. After this decrease, stability resumes at ~3.0 eV. Resistance to oxidation and reduction is also presented.« less

Low-temperature photoluminescence in NixMg1-xO nanocrystals

NASA Astrophysics Data System (ADS)

Churmanov, V. N.; Gruzdev, N. B.; Sokolov, V. I.; Pustovarov, V. A.; Ivanov, V. Yu.; Mironova-Ulmane, N. A.

2015-03-01

A study of the photoluminescence and photoluminescence excitation spectra of NixMg1-xO nanocrystals, at low-temperatures. We examine the processes of concentration quenching and supposed mechanisms of energy migration in NixMg1-xO. It is shown that the edge energies of the charge-transfer transitions in NixMg1-xO (x = 0.008) and NiO are practically identical.

Investigation of Thermal Conductivities and Expansion Coefficients of (Yb1 - x La x )2AlTaO7 Ceramics

NASA Astrophysics Data System (ADS)

Xiaoge, Chen; Hongsong, Zhang; Sai, Su; Yongde, Zhao; An, Tang; Haoming, Zhang

2017-12-01

The (Yb1 - x La x )2AlTaO7 ( x = 0, 0.1, 0.3, 0.5) ceramics were prepared by solid-state reaction method. The phase composition, microstructure, thermophysical properties of (Yb1 - x La x )2AlTaO7 ceramics were investigated. Results reveal that (Yb1 - x La x )2AlTaO7 ( x = 0, 0.1, 0.3) ceramics exhibit a single pyrochlore-type structure, and the (Yb0.5La0.5)2AlTaO7 has an orthorhombic weberite structure. The thermal conductivities of (Yb1 - x La x )2AlTaO7 ( x = 0, 0.1, 0.3) ceramics decrease with increasing Yb2O3 contents. (Yb0.5La0.5)2AlTaO7 has the highest thermal conductivity among all the ceramics studied, within the range of 1.48-1.75 W/m K (20-1200 °C). The thermal expansion coefficients of (Yb1 - x La x )2AlTaO7 ceramics decrease gradually with increasing La2O3 fractions, and the thermal expansion coefficients are close to those of YSZ.

Ce(x)O(y)⁻ (x = 2-3) + D₂O reactions: stoichiometric cluster formation from deuteroxide decomposition and anti-Arrhenius behavior.

PubMed

Felton, Jeremy A; Ray, Manisha; Waller, Sarah E; Kafader, Jared O; Jarrold, Caroline Chick

2014-10-30

Reactions between small cerium oxide cluster anions and deuterated water were monitored as a function of both water concentration and temperature in order to determine the temperature dependence of the rate constants. Sequential oxidation reactions of the Ce(x)O(y)⁻ (x = 2, 3) suboxide cluster anions were found to exhibit anti-Arrhenius behavior, with activation energies ranging from 0 to -18 kJ mol⁻¹. Direct oxidation of species up to y = x was observed, after which, -OD abstraction and D₂O addition reactions were observed. However, the stoichiometric Ce₂O₄⁻ and Ce₃O₆⁻ cluster anions also emerge in reactions between D₂O and the respective precursors, Ce₂O₃D⁻ and Ce₃O₅D₂⁻. Ce₂O₄⁻ and Ce₃O₆⁻ product intensities diminish relative to deuteroxide complex intensities with increasing temperature. The kinetics of these reactions are compared to the kinetics of the previously studied Mo(x)O(y)⁻ and W(x)O(y)⁻ reactions with water, and the possible implications for the reaction mechanisms are discussed.

Ultraviolet photodetector based on Mg{sub x}Zn{sub 1-x}O films using plasma-enhanced atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Yu-Chang; Lee, Hsin-Ying, E-mail: hylee@ee.ncku.edu.tw; Lee, Ching-Ting

2016-01-15

A plasma-enhanced atomic layer deposition (PE-ALD) system was used to deposit magnesium zinc oxide (Mg{sub x}Zn{sub 1−x}O) films with various Mg content (x). The Mg{sub x}Zn{sub 1-x}O films were applied to metal–semiconductor–metal ultraviolet (UV) photodetectors (MSM-UPDs) as an active layer. The Mg content in the Mg{sub x}Zn{sub 1-x}O films was modulated by adjusting the ZnO–MgO cycle ratios to 15:1, 12:1, and 9:1. Correspondingly, the Mg content in the Mg{sub x}Zn{sub 1-x}O films characterized using an energy dispersive spectrometer was 0.10, 0.13, and 0.16, respectively. The optical bandgap of the Mg{sub x}Zn{sub 1-x}O films increased from 3.56 to 3.66 eV withmore » an increase in Mg content from 0.10 to 0.16. The peak position of photoresponsivity for the Mg{sub x}Zn{sub 1-x}O MSM-UPDs was also shifted from 350 to 340 nm. The UV-visible rejection ratios of the Mg{sub x}Zn{sub 1-x}O MSM-UPDs were higher than 3 orders of magnitude. In addition, excellent detectivity and noise equivalent power for the Mg{sub x}Zn{sub 1-x}O MSM-UPDs were observed at a bias voltage of 5 V. The high performance of the Mg{sub x}Zn{sub 1-x}O MSM-UPDs was achieved by PE-ALD at a low temperature.« less

Epitaxial growth and properties of YBa2Cu3O(x)-Pb(Zr(0.6)Ti(0.4))O3-YBa2Cu3O(x) trilayer structure by laser ablation

NASA Astrophysics Data System (ADS)

Boikov, Iu. A.; Esaian, S. K.; Ivanov, Z. G.; Brorsson, G.; Claeson, T.; Lee, J.; Safari, A.

1992-08-01

YBa2Cu3O(x)Pb(Zr(0.6)Ti(0.4))O3-YBa2Cu3O(x) multilayer structure has been grown on SrTiO3 and Al2O3 substrates using laser ablation. The deposition conditions for the growth of trilayers and their properties are studied in this investigation. Scanning electron microscope images and X-ray diffraction analyses indicate that all the constituent films in the trilayer grow epitaxially on SrTiO3 and were highly oriented on Al2O3. Transport measurements on these multilayers show that top YBa2Cu3O(x) films have good superconducting properties.

Effect of interfacial SiO2- y layer and defect in HfO2- x film on flat-band voltage of HfO2- x /SiO2- y stacks for backside-illuminated CMOS image sensors

NASA Astrophysics Data System (ADS)

Na, Heedo; Lee, Jimin; Jeong, Juyoung; Kim, Taeho; Sohn, Hyunchul

2018-03-01

In this study, the effect of oxygen gas fraction during deposition of a hafnium oxide (HfO2- x ) film and the influence of the quality of the SiO2- y interlayer on the nature of flat-band voltage ( V fb) in TiN/HfO/SiO2- y /p-Si structures were investigated. X-ray photoemission spectroscopy analysis showed that the non-lattice oxygen peak, indicating an existing oxygen vacancy, increased as the oxygen gas fraction decreased during sputtering. From C- V and J- E analyses, the V fb behavior was significantly affected by the characteristics of the SiO2- y interlayer and the non-lattice oxygen fraction in the HfO2- x films. The HfO2- x /native SiO2- y stack presented a V fb of - 1.01 V for HfO2- x films with an oxygen gas fraction of 5% during sputtering. Additionally, the V fb of the HfO2- x /native SiO2- y stack could be controlled from - 1.01 to - 0.56 V by changing the deposition conditions of the HfO2- x film with the native SiO2- y interlayer. The findings of this study can be useful to fabricate charge-accumulating layers for backside-illuminated image sensor devices.

Topology-energy relationships and lowest energy configurations for pentagonal dodecahedral (H2O)20X clusters, X=empty, H2O, NH3, H3O+: The importance of O-topology

NASA Astrophysics Data System (ADS)

Anick, David J.

2010-04-01

For (H2O)20X water clusters consisting of X enclosed by the 512 dodecahedral cage, X=empty, H2O, NH3, and H3O+, databases are made consisting of 55-82 isomers optimized via B3LYP/6-311++G∗∗. Correlations are explored between ground state electronic energy (Ee) or electronic energy plus zero point energy (Ee+ZPE) and the clusters' topology, defined as the set of directed H-bonds. Linear regression is done to identify topological features that correlate with cluster energy. For each X, variables are found that account for 99% of the variance in Ee and predict it with a rms error under 0.2 kcal/mol. The method of analysis emphasizes the importance of an intermediate level of structure, the "O-topology," consisting of O-types and a list of O pairs that are bonded but omitting H-bond directions, as a device to organize the databases and reduce the number of structures one needs to consider. Relevant variables include three parameters, which count the number of H-bonds having particular donor and acceptor types; |M|2, where M is the cluster's vector dipole moment; and the projection of M onto the symmetry axis of X. Scatter diagrams for Ee or Ee+ZPE versus |M| show that clusters fall naturally into "families" defined by the values of certain discrete parameters, the "major parameters," for each X. Combining "family" analysis and O-topologies, a small group of clusters is identified for each X that are candidates to be the global minimum, and the minimum is determined. For X=H3O+, one cluster with central hydronium lies just 2.08 kcal/mol above the lowest isomer with surface hydronium. Implications of the methodology for dodecahedral (H2O)20(NH4+) and (H2O)20(NH4+)(OH-) are discussed, and new lower energy isomers are found. For MP2/TZVP, the lowest-energy (H2O)20(NH4+) isomer features a trifurcated H-bond. The results suggest a much more efficient and comprehensive way of seeking low-energy water cluster geometries that may have wide applicability.

Topology-energy relationships and lowest energy configurations for pentagonal dodecahedral (H2O)20X clusters, X = empty, H2O, NH3, H3O+: the importance of O-topology.

PubMed

Anick, David J

2010-04-28

For (H(2)O)(20)X water clusters consisting of X enclosed by the 5(12) dodecahedral cage, X = empty, H(2)O, NH(3), and H(3)O(+), databases are made consisting of 55-82 isomers optimized via B3LYP/6-311++G(**). Correlations are explored between ground state electronic energy (Ee) or electronic energy plus zero point energy (Ee+ZPE) and the clusters' topology, defined as the set of directed H-bonds. Linear regression is done to identify topological features that correlate with cluster energy. For each X, variables are found that account for 99% of the variance in Ee and predict it with a rms error under 0.2 kcal/mol. The method of analysis emphasizes the importance of an intermediate level of structure, the "O-topology," consisting of O-types and a list of O pairs that are bonded but omitting H-bond directions, as a device to organize the databases and reduce the number of structures one needs to consider. Relevant variables include three parameters, which count the number of H-bonds having particular donor and acceptor types; absolute value(M)(2), where M is the cluster's vector dipole moment; and the projection of M onto the symmetry axis of X. Scatter diagrams for Ee or Ee+ZPE versus absolute value(M) show that clusters fall naturally into "families" defined by the values of certain discrete parameters, the "major parameters," for each X. Combining "family" analysis and O-topologies, a small group of clusters is identified for each X that are candidates to be the global minimum, and the minimum is determined. For X = H(3)O(+), one cluster with central hydronium lies just 2.08 kcal/mol above the lowest isomer with surface hydronium. Implications of the methodology for dodecahedral (H(2)O)(20)(NH(4)(+)) and (H(2)O)(20)(NH(4)(+))(OH(-)) are discussed, and new lower energy isomers are found. For MP2/TZVP, the lowest-energy (H(2)O)(20)(NH(4)(+)) isomer features a trifurcated H-bond. The results suggest a much more efficient and comprehensive way of seeking low

Thermoelectric properties of LaRh(1-x)Ni(x)O(3).

PubMed

Shibasaki, S; Takahashi, Y; Terasaki, I

2009-03-18

We report measurements and analyses of resistivity, thermopower and thermal conductivity of polycrystalline samples of perovskite LaRh(1-x)Ni(x)O(3). The thermopower is found to be large at 800 K (185 µV K(-1) for x = 0.3), which is ascribed to the high-temperature stability of the low-spin state of Rh(3+)/Rh(4+) ions. This clearly contrasts with the thermopower of the isostructural oxide LaCoO(3), which rapidly decreases above 500 K owing to the spin-state transition. The spin state of the transition-metal ions is one of the most important parameters in oxide thermoelectrics.

Spectroscopy of charge transfer states in Mg1 - x Ni x O

NASA Astrophysics Data System (ADS)

Churmanov, V. N.; Sokolov, V. I.; Pustovarov, V. A.; Gruzdev, N. B.; Mironova-Ulmane, N.

2016-10-01

Photoluminescence and photoluminescence excitation spectra of solid solution Mg1- x Ni x O ( x = 0.008) have been analyzed. The contributions of charge transfer electronic states and nonradiative Auger relaxation to the formation of the photoluminescence spectrum are discussed.

Photoemission properties of Eu-doped Zr1- x Ce x O2 (x = 0-0.2) nanoparticles prepared by hydrothermal method

NASA Astrophysics Data System (ADS)

Ozawa, Masakuni; Matsumoto, Masashi; Hattori, Masatomo

2018-01-01

Photoluminescent Eu-doped ZrO2 and Zr1- x Ce x O2 (x = 0-0.2) nanoparticles were prepared by a hydrothermal method. X-ray diffraction and Raman spectra indicated the formation of tetragonal crystals of ZrO2 and its solid solutions with a grain size of less than 10 nm diameter after heat treatment at 400 °C. The photoemission spectra of Zr1- x Ce x O2:Eu3+ nanocrystalline samples showed the typical emission of Eu3+ ions assigned to 5D0 → 7F1 (590 nm) and 5D0 → 7F2 (610 nm) transitions and additional emissions of 5D0 → 7F J with higher J of 3-5. Increasing the CeO2 concentration reduced the emission intensity, and the emission peak shift was affected by a local lattice distortion, i.e., CeO2 concentration. The present study provided fundamental knowledge that is expected to enable the fabrication of ZrO2-based nanocrystal phosphor materials and a measure for controlling the emission peak shift and intensity in oxide fluorite-based phosphor.

Evaluation of band alignment of α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterostructures by X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Uchida, Takayuki; Jinno, Riena; Takemoto, Shu; Kaneko, Kentaro; Fujita, Shizuo

2018-04-01

The band alignment at an α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterointerface, with different Al compositions (x), grown on a c-plane sapphire substrate was evaluated by X-ray photoelectron spectroscopy. The experimental results show that the heterointerface has the type-I band discontinuity with the valence band offsets of 0.090, 0.12, and 0.14 eV, and the conduction band offsets of 0.34, 0.79, and 1.87 eV, for x values of 0.1, 0.4, and 0.8, respectively. The small band offset for the valence band is attributed to the fact that the valence band of oxides is constituted by the localized O 2p level, which is dominated by the nature of oxygen atoms. The type-I band discontinuity is desirable for a variety of heterostructure devices.

ZrO2-modified mesoporous nanocrystalline TiO2-xNx as efficient visible light photocatalysts.

PubMed

Wang, Xinchen; Yu, Jimmy C; Chen, Yilin; Wu, Ling; Fu, Xianzhi

2006-04-01

Mesoporous nanocrystalline TiO2-xNx and TiO2-xNx/ZrO2 visible-light photocatalysts have been prepared by a sol-gel method. The photocatalysts were characterized by XRD, N2 adsorption-desorption, TEM, XPS, UV/Vis, and IR spectroscopy. The photocatalytic activity of the samples was evaluated by the decomposition of ethylene in air under visible light (lambda > 450 nm) illumination. Results revealed that nitrogen was doped into the lattice of TiO2 by the thermal treatment of NH3-adsorbed TiO2 hydrous gels, converting the TiO2 into a visible-light responsive catalyst. The introduction of ZrO2 into TiO2-xNx considerably inhibits the undesirable crystal growth during calcination. Consequently, the ZrO2-modified TiO2-xNx displays higher porosity, higher specific surface area, and an improved thermal stability over the corresponding unmodified TiO2-xNx samples.

Fabrication of Coaxial Si1- x Ge x Heterostructure Nanowires by O2 Flow-Induced Bifurcate Reactions

NASA Astrophysics Data System (ADS)

Kim, Ilsoo; Lee, Ki-Young; Kim, Ungkil; Park, Yong-Hee; Park, Tae-Eon; Choi, Heon-Jin

2010-10-01

We report on bifurcate reactions on the surface of well-aligned Si1- x Ge x nanowires that enable fabrication of two different coaxial heterostructure nanowires. The Si1- x Ge x nanowires were grown in a chemical vapor transport process using SiCl4 gas and Ge powder as a source. After the growth of nanowires, SiCl4 flow was terminated while O2 gas flow was introduced under vacuum. On the surface of nanowires was deposited Ge by the vapor from the Ge powder or oxidized into SiO2 by the O2 gas. The transition from deposition to oxidation occurred abruptly at 2 torr of O2 pressure without any intermediate region and enables selectively fabricated Ge/Si1- x Ge x or SiO2/Si1- x Ge x coaxial heterostructure nanowires. The rate of deposition and oxidation was dominated by interfacial reaction and diffusion of oxygen through the oxide layer, respectively.

Fabrication of Coaxial Si(1-x)Ge(x) Heterostructure Nanowires by O(2) Flow-Induced Bifurcate Reactions.

PubMed

Kim, Ilsoo; Lee, Ki-Young; Kim, Ungkil; Park, Yong-Hee; Park, Tae-Eon; Choi, Heon-Jin

2010-06-17

We report on bifurcate reactions on the surface of well-aligned Si(1-x)Ge(x) nanowires that enable fabrication of two different coaxial heterostructure nanowires. The Si(1-x)Ge(x) nanowires were grown in a chemical vapor transport process using SiCl(4) gas and Ge powder as a source. After the growth of nanowires, SiCl(4) flow was terminated while O(2) gas flow was introduced under vacuum. On the surface of nanowires was deposited Ge by the vapor from the Ge powder or oxidized into SiO(2) by the O(2) gas. The transition from deposition to oxidation occurred abruptly at 2 torr of O(2) pressure without any intermediate region and enables selectively fabricated Ge/Si(1-x)Ge(x) or SiO(2)/Si(1-x)Ge(x) coaxial heterostructure nanowires. The rate of deposition and oxidation was dominated by interfacial reaction and diffusion of oxygen through the oxide layer, respectively.

New Defective Brannerite-Type Vanadates. I. Synthesis and Study of Mn 1- x- yφ xNa yV 2-2 x-yMo 2 x+yO 6 Solid Solutions

NASA Astrophysics Data System (ADS)

Masłowska, Bogna; Ziółkowski, Jacek

1994-05-01

MnV 2O 6 of the brannerite-type structure (below 540°C) doped with MoO 3 and Na 2O forms isomorphous solid solutions MnNaφ = Mn 1- x-yφ xNa yV 2-2 x-yMo 2 x+ yO 6 (φ cation vacancy in the original Mn position), belonging to the pseudoternary MnV 2O 6-NaVMoO 6-MoO 3 system. Particular cases are MnNa = Mn 1- yNa y V 2- yMo yO 6 ( x = 0), Mnφ = Mn 1- xφ xV 2-2 xMo 2 xO 6 ( y = 0), and Naφ = Na 1- xφ xV 1- xMo 1+ xO 6 ( x + y = 1). MnV 2O 6 and NaVMoO 6 show miscibility in the entire composition range (MnNa). The opposite boundary of MnNaφ passes through the (100 x, 100 y) points (45, 0), (33, 30), and (30, 70). The phase diagram of the pseudobinary MnV 2O 6-NaVMoO 6 system (determined with DTA) shows (i) a narrow double-lens-type solidus-liquidus gap at high values of y , (ii) two peritectic meltings at lower y (yielding the high temperature β-MnNa and Mn 2V 2O 7), and (iii) little area of β-MnNa. Lattice parameters of MnNa (determined with X-ray diffraction) reveal small deviations from Vegard's law. As the ionic radii of both dopants (Na + and Mo 6+) are, respectively, larger than those of mother ions (Mn 2+ and V 5+), the unit cell increases in all directions with rising y along the MnNa series of solid solutions. However, due to the anisotropy of the structure, parameter c is strongly sensitive to Na/Mn substitution, b is ruled by Mo/V, and a is weakly influenced by Mo/V. Close analogy to the behavior of the previously studied MnV 2O 6-LiVMoO 6-MoO 6 system is discussed.

Phase transformation in (0.90- x)Pb(Mg 1/3Nb 2/3)O 3- xPbTiO 3-0.10PbZrO 3 piezoelectric ceramic: X-ray diffraction and Raman investigation

NASA Astrophysics Data System (ADS)

Xia, Zhiguo; Li, Qiang

2007-05-01

Piezoelectric ceramics with compositions of (0.90- x)Pb(Mg 1/3Nb 2/3)O 3- xPbTiO 3-0.10PbZrO 3, x=0.28, 0.31, 0.34, 0.37, 0.40 and 0.43, were prepared using the conventional columbite precursor method, and their structural phase transformation and piezoelectric behaviors near the morphotropic phase boundary (MPB) have been systematically investigated as a function of PbTiO 3 content. X-ray diffraction (XRD) results demonstrate that the structure of the ceramics experiences a gradual transition process from rhombohedral phase to tetragonal phase with the increasing of PbTiO 3 content, and that compositions with x=0.34-0.40 lie in the MPB region of this ternary system. A Raman spectra investigation of the ceramic samples testified to the transformation process of rhombohedral phase to tetragonal phase by comparing the relative intensities of tetragonal E(2TO 1) mode and rhombohedral phase R h mode. The structure information was also correlated to the parabola change of the piezoelectric constant; the maximum piezoelectric constants were obtained near the MPB region.

Fragility Index variation in (Li2O)x(B2O3) 100-x melts

NASA Astrophysics Data System (ADS)

Skipper, Charles; Chbeir, Ralph; Mohanty, Chandi; Boolchand, Punit

We have measured the fragility index (m) of titled melts as a function of Li2O content in the 0<x<35% range using Modulated DSC. In this approach, one measures the real and imaginary part of the complex specific heat as a function of modulation frequency (ν) , and deduces an activation energy by plotting the log of the enthalpy relaxation time as a function of inverse Temperature obtained at various ν. For pure B2O3 glass with a Tg = 308°C, we obtain m = 28 (1). With increasing x, m is found to monotonically increase to 38(1) as x increased to 15%, but then to plateau at a value of m = 42(2) in the range 18%<x<25%. These values in m are significantly lower than those reported earlier. In particular, the range of x where we observe a plateau in m, authors of ref. 1 observed a linear increase in the 41x across which a plateau is observed also happens to coincide where the isostatically rigid Intermediate Phase reported recently.

Synthesis, Characterization, and Gas-Sensing Properties of Mesoporous Nanocrystalline Sn(x)Ti(1-x)O2.

PubMed

Zhong, Cheng; Lin, Zhidong; Guo, Fei; Wang, Xuehua

2015-06-01

A nanocomposite mesoporous material composed by SnO2 and TiO2 with the size of -5-9 nm were prepared via a facile wet-chemical approach combining with an annealing process. The microstructure of obtained Sn(x)Ti(1-x)O2 powders were characterized by X-ray diffraction, X-ray Photo-electronic Spectroscopy, scanning electron microscope, transmission electron microscope and nitrogen adsorption-desorption experiment. The gas sensing performances to several gases of the mesoporous material were studied. The sensors of Sn(x)Ti(1-x)O2 (ST10, with 9.1% Ti) exhibited very high responses to volatile organic compounds at 160 degrees C. The order of the responses to volatile gases based on ST10 was ethanol > formaldehyde > acetone > toluene > benzene > methane. Sensor based on ST10 displays a highest sensitivity to hydrogen at 200 degrees C. Sensor responses to H2 at 200 degrees C have been measured and analyzed in a wide concentration range from 5 to 2000 ppm. The solid solution Sn(x)Ti(1-x)O2 can be served as a potential gas-sensing material for a broad range of future sensor applications.

Thermoelectric properties of Ca(1-x-y)Dy(x)CeyMnO3 for power generation.

PubMed

Park, K; Lee, G W; Jung, J; Kim, S-J; Lim, Y-S; Choi, S-M; Seo, W-S

2011-08-01

The sintered Ca(1-x-y)Dy(x)CeyMnO3 bodies were a single phase with a perovskite structure without any impurity phases. The calculated crystallite sizes of the Ca(1-x-y)Dy(x)CeyMnO3 were in the range of 43.3 to 63.3 nm. The composition significantly affected their microstructural and thermoelectric characteristics. The doped Dy led to both an increase in the electrical conductivity as well as the absolute value of the Seebeck coefficient, resulting in an enhanced power factor. The highest power factor (5.1 x 10(-4) Wm(-1) K(-2)) was obtained for Ca(0.8)Dy(0.2)MnO3 at 800 degrees C. In this study, we systematically discussed the thermoelectric properties of the Ca(1-x-y)Dy(x)CeyMnO3, with respect to the substitution of Dy and/or Ce for Ca.

Interaction of Ce{sub 1−x}Er{sub x}O{sub 2−y} nanoparticles with SiO{sub 2}-effect of temperature and atmosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kepinski, L., E-mail: L.Kepinski@int.pan.wroc.pl; Krajczyk, L.; Mista, W.

2014-01-15

Morphology, microstructure and phase evolution of homogeneous, nanocrystalline Ce{sub 1−x}Er{sub x}O{sub 2−x/2} mixed oxide (x=0.3 and 0.5), prepared by microemulsion method, supported on amorphous SiO{sub 2} was studied in oxidizing and reducing atmosphere by XRD, TEM, SEM-EDS and N{sub 2} adsorption. The system is structurally and chemically stable in the oxidizing atmosphere up to 1000 °C, exhibiting only a small increase of the mean crystallite size of the oxide to ∼4 nm. At 1100 °C formation of Er silicate with unusual structure isomorphic with y-Y{sub 2}Si{sub 2}O{sub 7} (yttrialite), stabilized by Ce{sup 4+} ions was observed. In the reducing atmospheremore » the Ce{sub 1−x}Er{sub x}O{sub 2−x/2} reacted with SiO{sub 2} already at 900 °C, due to high affinity of the reduced Ce{sup 3+} to form a silicate phase. At higher temperature the silicate crystallized into the tetragonal, low temperature A-(Ce{sub 1−x}Er{sub x}){sub 2}Si{sub 2}O{sub 7} polymorph. Such systems, containing nanocrystalline silicate particles with Er{sup 3+} ions placed in well defined sites embedded in silica matrix, may be interesting as highly efficient active components of optical waveguides amplifiers integrated with Si microelectronics. The nanocrystalline Ce–Er–O/SiO{sub 2} system prepared by the impregnation of the silica with the aqueous solution of nitrates appeared to be chemically inhomogeneous and less stable in both oxidising and reducing atmosphere. - Graphical abstract: Structure evolution of Ce{sub 0.5}Er{sub 0.5}O{sub 1.75} in air and in H{sub 2}. Display Omitted - Highlights: • Homogeneous 3 nm Ce{sub 1−x}Er{sub x}O{sub 2−y} particles were prepared and uniformly dispersed on SiO{sub 2}. • Er diffusion to SiO{sub 2} determines the stability of the mixed oxide in air to ∼1000 °C. • Spreading of Ce{sub 1−x}Er{sub x}O{sub 2−y} onto SiO{sub 2} occurs in hydrogen at 900 °C. • Nanocrystalline A-(Ce,Er){sub 2}Si{sub 2}O{sub 7} silicate

Structure, glass transition temperature and spectroscopic properties of 10Li2O-xP2O5-(89-x)TeO2-1CuO (5≤x≤25 mol%) glass system.

PubMed

Upender, G; Babu, J Chinna; Mouli, V Chandra

2012-04-01

X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrometry (EDS), differential scanning calorimetry (DSC), infrared (IR), Raman, electron paramagnetic resonance (EPR) and optical absorption studies on 10Li2O-xP2O5-(89-x)TeO2-1CuO glasses (where x=5, 10, 15, 20 and 25 mol%) have been carried out. The amorphous nature of the glasses was confirmed using XRD and FESEM measurements. The glass transition temperature (Tg) of glass samples have been estimated from DSC traces and found that the Tg increases with increasing P2O5 content. Both the IR and Raman studies have been showed that the present glass system consists of [TeO3], [TeO4], [PO3] and [PO4] units. The spin-Hamiltonian parameters such as g∥, g⊥, and A∥ have been determined from EPR spectra and it was found that the Cu2+ ion is present in tetragonal distorted octahedral site with [Formula: see text] as the ground state. Bonding parameters and bonding symmetry of Cu2+ ions have been calculated by correlating EPR and optical data and were found to be composition dependent. Copyright © 2012 Elsevier B.V. All rights reserved.

Structural and electrochemical properties of La 0.8Sr 0.2Ga 1-xFe xO 3

NASA Astrophysics Data System (ADS)

Mori, Kazuhiro; Onodera, Yohei; Kiyanagi, Ryoji; Richardson, James W.; Itoh, Keiji; Sugiyama, Masaaki; Kamiyama, Takashi; Fukunaga, Toshiharu

2009-02-01

Mixed ionic-electronic conductor of Fe doped lanthanum gallate, La 0.8Sr 0.2Ga 1-xFe xO 3, has been studied by the dc four-probe method and the neutron powder diffraction. In the electrical conductivity measurement at RT, insulator-metal transition-like phenomenon was observed at around x˜0.35; this suggests an existence of the percolation limit for the electronic conductivity. Simultaneously, a bond length between O atoms, lO-O, in a MO 6 octahedron (M dbnd Ga 1-xFe x) drastically expands over x˜0.4, according to the result of crystal structure refinement based on the hexagonal phase. Such a drastic expansion in the lO-O would induce the decrease in the oxygen ionic conductivity.

Investigations of the local distortions and EPR parameters for Cu2+ in xNa2 O-(30-x)K2 O-70B2 O3 (5 ≤ x ≤ 25 mol%) glasses.

PubMed

Zhang, Zhen-Ya; Wu, Shao-Yi; Zhang, Fu; Zhang, Cheng-Xi; Qin, Rui-Jie; Gao, Han

2018-03-01

The local distortions and electron paramagnetic resonance parameters for Cu 2+ in the mixed alkali borate glasses xNa 2 O-(30-x)K 2 O-70B 2 O 3 (5 ≤ x ≤ 25 mol%) are theoretically studied with distinct modifier Na 2 O compositions x. Owing to the Jahn-Teller effect, the octahedral [CuO 6 ] 10- clusters show significant tetragonal elongation ratios p ~19% along the C 4 axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi-linearly decreasing tendencies, respectively, whereas the relative tetragonal elongation ratio p has quasi-linearly increasing rule with some fluctuations, leading to the minima of g factors at x = 10 mol%. The composition dependences of the optical spectra and the electron paramagnetic resonance parameters are suitably reproduced by the linear or quasi-linear relationships of the relevant quantities (i.e., Dq, k, and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal-fields and the electronic cloud distribution around Cu 2+ with the variation of the composition of Na 2 O. Copyright © 2017 John Wiley & Sons, Ltd.

Water electrolysis on La 1-xSr xCoO 3-δ perovskite electrocatalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mefford, J. Tyler; Rong, Xi; Abakumov, Artem M.

2016-03-23

Perovskite oxides are attractive candidates as catalysts for the electrolysis of water in alkaline energy storage and conversion systems. However, the rational design of active catalysts has been hampered by the lack of understanding of the mechanism of water electrolysis on perovskite surfaces. Key parameters that have been overlooked include the role of oxygen vacancies, B–O bond covalency, and redox activity of lattice oxygen species. Here we present a series of cobaltite perovskites where the covalency of the Co–O bond and the concentration of oxygen vacancies are controlled through Sr 2+ substitution into La 1-xSr xCoO 3-δ. We attempt tomore » rationalize the high activities of La 1-xSr xCoO 3-δ through the electronic structure and participation of lattice oxygen in the mechanism of water electrolysis as revealed through ab initio modelling. Using this approach, we report a material, SrCoO 2.7, with a high, room temperature-specific activity and mass activity towards alkaline water electrolysis.« less

Water electrolysis on La 1-xSr xCoO 3-δ perovskite electrocatalysts

DOE PAGES

Mefford, J. Tyler; Rong, Xi; Abakumov, Artem M.; ...

2016-03-23

Here, perovskite oxides are attractive candidates as catalysts for the electrolysis of water in alkaline energy storage and conversion systems. However, the rational design of active catalysts has been hampered by the lack of understanding of the mechanism of water electrolysis on perovskite surfaces. Key parameters that have been overlooked include the role of oxygen vacancies, B–O bond covalency, and redox activity of lattice oxygen species. Here we present a series of cobaltite perovskites where the covalency of the Co–O bond and the concentration of oxygen vacancies are controlled through Sr 2+ substitution into La 1–xSr xCoO 3–δ. We attemptmore » to rationalize the high activities of La 1–xSr xCoO 3–δ through the electronic structure and participation of lattice oxygen in the mechanism of water electrolysis as revealed through ab initio modelling. Using this approach, we report a material, SrCoO 2.7, with a high, room temperature-specific activity and mass activity towards alkaline water electrolysis.« less

Electrical conductivity and thermoelectric power of La1- x Li x CoO3-δ (0 ≤ x ≤ 0.1) oxides

NASA Astrophysics Data System (ADS)

Vecherskii, S. I.; Konopel'ko, M. A.; Batalov, N. N.; Antonov, B. D.; Reznitskikh, O. G.; Yaroslavtseva, T. V.

2016-12-01

The influence of the concentration of lithium ions on the phase composition, the electrical conductivity, and the thermoelectric power of La1- x Li x CoO3-δ (0 ≤ x ≤ 0.1) oxides synthesized by the ceramic method has been investigated. It has been found that the region of the existence of perovskite-type La1- x Li x CoO3-δ solid solutions does not exceed x = 0.05. The doping with lithium leads to an increase in the electrical conductivity of single-phase samples in comparison with that of the LaCoO3 compound. As the temperature increases from 300 to 400 K, the thermoelectric power of the LaCoO3 compound increases from the negative to positive values and then decreases, but remains positive in the temperature range from 400 to 1020 K. The thermoelectric power of the other samples has a positive sign. The results obtained have been discussed based on the models of the electron density of states in LaCoO3 and La1- x Sr x CoO3-δ, proposed in the studies of Señarís-Rodríguez and Goodenough, as well as in the framework of the theory of non-crystalline materials, developed by Mott.

X-ray Photoelectron Spectroscopy study of CaV1-xMoxO3-δ

NASA Astrophysics Data System (ADS)

Belyakov, S. A.; Kuznetsov, M. V.; Shkerin, S. N.

2018-06-01

An investigation was carried out on perovskite-based derivatives of CaV1-xMoxO3-δ using X-ray Photoelectron Spectroscopy (XPS). According to the XRD pattern, the area of homogeneity covers the region from x = 0 to x = 0.6. Wide XPS-peaks of Ca, V, Mo and O are observed, signalling that elements are presented in multiple states. A model for explaining the large chemical shifts of XPS peaks due to different charging effects on different parts of the sample surface is proposed.

Synthesis, characterization and ferromagnetic properties of Zn1-xMnxO (x ≤ 0.05) nanoparticles

NASA Astrophysics Data System (ADS)

Phuruangrat, Anukorn; Thongtem, Titipun; Thongtem, Somchai

2018-06-01

Zn1-xMnxO (x ≤ 0.05) nanoparticles were synthesized by a combination of room temperature precipitation and high temperature calcination. Pure hexagonal wurtzite ZnO nanoparticles with the size of ≤100 nm and a dominant vibrational peak at 437 cm-1 of E2H non-polar optical phonon mode were detected. The present research was succeeded in doping of ZnO lattice by Mn2+ ions, including the detection of an additional peak at 528 cm-1 associated with lattice defects. Magnetic properties of Zn1-xMnxO (x ≤ 0.05) nanoparticles were controlled by correlated spin of Mn-O-Mn exchange couple and lattice disorder. The saturation magnetization of ferromagnetic Zn0.97Mn0.03O was the highest at 51.49 × 10-3 emu/g.

(3+1)D superspace structural determination of two new modulated composite phases: Sr 1+ x(Cu xMn 1- x)O 3; x=3/11 and x=0.3244

NASA Astrophysics Data System (ADS)

El Abed, Ahmed; Gaudin, Etienne; zur Loye, Hans-Conrad; Darriet, Jacques

2003-01-01

We report the structure determination of two new phases belonging to the A 1+ x(A' xB 1- x)O 3 family of oxides with A=Sr, A'=Cu, and B=Mn, where x=3/11 and x=0.3244, corresponding to a commensurate and incommensurate composite structure, respectively. These two compounds are the first examples of oxides belonging to the Sr 1+ x(Cu xMn 1- x)O 3 family. Their structures were solved in the (3+1) dimensional superspace formalism as modulated composite structures with two subsystems [(Cu,Mn)O 3] and [Sr]. The superspace group used to solve the structures is R 3¯m(00γ)0s . The first phase ( x=3/11), corresponding to the chemical formula Sr 14Cu 3Mn 8O 33, was obtained as a single crystal with unit cell parameters of a=9.6025(3) Å and c1=2.5660(8) Å ( q=7/11 c1∗, Z=3), where c1 is the lattice parameter corresponding to the c-axis of the trigonal subsystem [(Cu,Mn)O 3]. The second phase ( x=0.3244(1)), is a polycrystalline sample with unit cell parameters of a=9.5933(7) and c1=2.5933(3) ( q=0.6622 c1∗, Z=3). In both structures, one dimensional chains run along the c-axis which contain octahedra and trigonal prisms occupied by manganese and copper atoms, respectively. The refinement results show that in both cases copper occupies the rectangular faces of the trigonal prism while manganese occupies the octahedral sites. The magnetic measurements of the polycrystalline phase (Sr 1+ x(Cu xMn 1- x)O 3, x=0.3244(2)) and the Curie constant obtained from the high temperature susceptibility are in agreement with a spin state configuration of S=3/2 for Mn 4+ and S=1/2 for Cu 2+.

Synthesis and morphology of Ba1-xRE2x/3Nb2O6 nanocrystals with tungsten bronze structure in RE2O3-BaO-Nb2O5-B2O3 glasses (RE: Sm, Eu, Gd, Dy, Er)

NASA Astrophysics Data System (ADS)

Ida, H.; Shinozaki, K.; Honma, T.; Oh-ishi, K.; Komatsu, T.

2012-12-01

Ba1-xRE2x/3Nb2O6 nanocrystals with a tetragonal tungsten bronze (TTB) structure are synthesized using a conventional glass crystallization technique in 2.3RE2O3-27.4BaO-34.3Nb2O5-36B2O3 (mol%) (RE=Sm, Eu, Gd, Dy, and Er) glasses. One sharp crystallization peak is observed at ∼670 °C in both powdered and bulk glasses, and the formation of Ba1-xRE2x/3Nb2O6 nanocrystals with unit cell parameters of a∼1.24 nm and c∼0.39 nm was confirmed. It is found from high resolution transmission electron microscope observations that the morphology of Ba1-xRE2x/3Nb2O6 nanocrystals is ellipsoidal. Their average particle size is in the range of 15-60 nm and decreases with decreasing ionic radius of RE3+ being present in the precursor glasses. The optical transparent crystallized glass (bulk) shows the total photoluminescence (PL) quantum yield of 53% in the visible region of Eu3+ ions, suggesting a high potential of Ba1-xRE2x/3Nb2O6 nanocrystals as PL materials.

Average and local crystal structures of (Ga 1–xZn x)(N 1–xO x) solid solution nanoparticles

DOE PAGES

Feygenson, Mikhail; Neuefeind, Joerg C.; Tyson, Trevor A.; ...

2015-11-06

We report the comprehensive study of the crystal structure of (Ga 1–xZn x)(N 1–xO x) solid solution nanoparticles by means of neutron and synchrotron x-ray scattering. In our study we used four different types of (Ga 1–xZn x)(N 1–xO x) nanoparticles, with diameters of 10–27 nm and x = 0.075–0.51, which show the narrow energy-band gaps from 2.21 to 2.61 eV. The Rietveld analysis of the neutron diffraction data revealed that the average crystal structure is the hexagonal wurtzite (space group P6 3mc), in agreement with previous reports on similar bulk materials. The pair-distribution function (PDF) analysis of the samemore » data found that the local structure is more disordered than the average one. It is best described by the model with a lower symmetry space group P1, where atoms are quasirandomly distorted from their nominal positions in the hexagonal wurtzite lattice.« less

Investigation of novel inverted NiO@NixCo1-xO core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Hasan, Samiul; Mayanovic, R. A.; Benamara, Mourad

2018-05-01

Inverse core-shell nanoparticles, comprised of an antiferromagnetic (AFM) core covered by a ferromagnetic (FM) or ferrimagnetic (FiM) shell, are of current interest due to their different potential application and due to the tunability of their magnetic properties. The antiferromagnetic nature of NiO and high Néel temperature (523 K) makes this material well suited for inverse core-shell nanoparticle applications. Our primary objective in this project has been to synthesize and characterize inverted core-shell nanoparticles (CSNs) comprised of a NiO (AFM) core and a shell consisting of a NixCo1-xO (FiM) compound. The synthesis of the CSNs was made using a two-step process. The NiO nanoparticles were synthesized using a chemical reaction method. Subsequently, the NiO nanoparticles were used to grow the NiO@NixCo1-xO CSNs using our hydrothermal nano-phase epitaxy method. XRD structural characterization shows that the NiO@NixCo1-xO CSNs have the rock salt cubic crystal structure. SEM-EDS data indicates the presence of Co in the CSNs. Magnetic measurements show that the CSNs exhibit AFM/FiM characteristics with a small coercivity field of 30 Oe at 5 K. The field cooled vs zero field cooled hysteresis loop measurements show a magnetization axis shift which is attributed to the exchange bias effect between the AFM NiO core and an FiM NixCo1-xO shell of the CSNs. Our ab initio based calculations of the NixCo1-xO rock salt structure confirm a weak FiM character and a charge transfer insulator property of the compound.

Crystal structure study of dielectric oxynitride perovskites La{sub 1−x}Sr{sub x}TiO{sub 2+x}N{sub 1−x} (x=0, 0.2)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habu, Daiki; Masubuchi, Yuji; Torii, Shuki

As is the case with SrTaO{sub 2}N, both cis-ordering of nitride anions and octahedral titling are also preferable in La{sub 1−x}Sr{sub x}TiO{sub 2+x}N{sub 1−x} (x=0, 0.2) oxynitride perovskites. A larger dielectric constant of ε{sub r}≈5.0×10{sup 3} was estimated for the pure oxynitride with x=0.2, compared with ε{sub r}≈750 for the product with x=0, by extrapolating the ε{sub r} values obtained from powders mixed with paraffin at various mixing ratios. The crystal structure of x=0.2 with larger tolerance factor than x=0 increased the octahedral tilting, which contributes to the increased dielectric constant. The increased dielectric constant supports the exchange mechanism formore » the dielectric property between two kinds of –Ti–N– helical coils (clockwise and anticlockwise) derived from the above cis-ordering of nitride anions. - Graphical abstract: Very large dielectric constant values were estimated for La{sub 1−x}Sr{sub x}TiO{sub 2+x}N{sub 1−x}; ε{sub r}≈5.0×10{sup 3} in x=0.2 and ε{sub r}≈750 in x=0. - Highlights: • Cis-configuration of nitride anions was confirmed in La{sub 1−x}Sr{sub x}TiO{sub 2+x}N{sub 1−x} (x=0, 0.2). • Dielectric constant values were estimated to be 750 for x=0 and 5.0×10{sup 3} for x=0.2, respectively. • The large dielectric property is to the exchange mechanism between clockwise and anticlockwise –Ti–N– coil motifs.« less

Structure Evolution and Reactivity of the Sc(2- x)V xO3+δ (0 ≤ x ≤ 2.0) System.

PubMed

Lussier, Joey A; Simon, Fabian J; Whitfield, Pamela S; Singh, Kalpana; Thangadurai, Venkataraman; Bieringer, Mario

2018-05-07

Solid oxide fuel cells (SOFCs) are solid-state electrochemical devices that directly convert chemical energy of fuels into electricity with high efficiency. Because of their fuel flexibility, low emissions, high conversion efficiency, no moving parts, and quiet operation, they are considered as a promising energy conversion technology for low carbon future needs. Solid-state oxide and proton conducting electrolytes play a crucial role in improving the performance and market acceptability of SOFCs. Defect fluorite phases are some of the most promising fast oxide ion conductors for use as electrolytes in SOFCs. We report the synthesis, structure, phase diagram, and high-temperature reactivity of the Sc (2- x) V x O 3+δ (0 ≤ x ≤ 2.00) oxide defect model system. For all Sc (2- x) V x O 3.0 phases with x ≤ 1.08 phase-pure bixbyite-type structures are found, whereas for x ≥ 1.68 phase-pure corundum structures are reported, with a miscibility gap found for 1.08 < x < 1.68. Structural details obtained from the simultaneous Rietveld refinements using powder neutron and X-ray diffraction data are reported for the bixbyite phases, demonstrating a slight V 3+ preference toward the 8b site. In situ X-ray diffraction experiments were used to explore the oxidation of the Sc (2- x) V x O 3.0 phases. In all cases ScVO 4 was found as a final product, accompanied by Sc 2 O 3 for x < 1.0 and V 2 O 5 when x > 1.0; however, the oxidative pathway varied greatly throughout the series. Comments are made on different synthesis strategies, including the effect on crystallinity, reaction times, rate-limiting steps, and reaction pathways. This work provides insight into the mechanisms of solid-state reactions and strategic guidelines for targeted materials synthesis.

Structural and optical characterization of ZnO/Mg(x)Zn(1-x)O multiple quantum wells based random laser diodes.

PubMed

Jiang, Qike; Zheng, He; Wang, Jianbo; Long, Hao; Fang, Guojia

2012-12-01

Two kinds of laser diodes (LDs) comprised of ZnO/Mg(x)Zn(1-x)O (ZnO/MZO) multiple quantum wells (MQWs) grown on GaN (MQWs/GaN) and Si (MQWs/Si) substrates, respectively, have been constructed. The LD with MQWs/GaN exhibits ultraviolet random lasing under electrical excitation, while that with MQWs/Si does not. In the MQWs/Si, ZnO/MZO MQWs consist of nanoscaled crystallites, and the MZO layers undergo a phase separation of cubic MgO and hexagonal ZnO. Moreover, the Mg atom predominantly locates in the MZO layers along with a significant aggregation at the ZnO/MZO interfaces; in sharp contrast, the ZnO/MZO MQWs in the MQWs/GaN show a well-crystallized structure with epitaxial relationships among GaN, MZO, and ZnO. Notably, Mg is observed to diffuse into the ZnO well layers. The structure-optical property relationship of these two LDs is further discussed.

Structural and ferroelectric phase evolution in [KNbO3]1-x[BaNi1/2Nb1/2O3-δ]x (x = 0, 0.1)

NASA Astrophysics Data System (ADS)

Hawley, Christopher; Wu, Liyan; Xiao, Geoffrey; Grinberg, Ilya; Rappe, Andrew; Davies, Peter; Spanier, Jonathan

The phase transition evolution for [KNbO3]1-x[BaNi1/2Nb1/2O3-δ]x (x=0, 0.1) is determined via complementary dielectric constant and Raman scattering measurements. Raman scattering by optical phonons over the range of 100-1000 cm-1 for -190°C < T < 600°C reveals six discernible zone-center optical phonon modes. They are assigned to structural and ferroelectric phases in the solid solution x = 0.1 and compared with those for end member x = 0 and with the results of temperature-dependent dielectric permittivity. Rigorous peak fitting analyses of spectra collected from the solid solution and end member indicate structural and ferroelectric phase transition temperatures that are quite close to those for the KNbO3 end member. Remarkably, despite the inclusion of 5 atomic Work supported by US ARO under W911NF-14-1-0500, NSF 1123696, and DoE BES under DE-FG02-07ER46431. Equipment acquisitions and computational support under DURIP and DoE NERSCC.

Band gap bowing in NixMg1−xO

PubMed Central

Niedermeier, Christian A.; Råsander, Mikael; Rhode, Sneha; Kachkanov, Vyacheslav; Zou, Bin; Alford, Neil; Moram, Michelle A.

2016-01-01

Epitaxial transparent oxide NixMg1−xO (0 ≤ x ≤ 1) thin films were grown on MgO(100) substrates by pulsed laser deposition. High-resolution synchrotron X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the thin films are compositionally and structurally homogeneous, forming a completely miscible solid solution. Nevertheless, the composition dependence of the NixMg1−xO optical band gap shows a strong non-parabolic bowing with a discontinuity at dilute NiO concentrations of x < 0.037. Density functional calculations of the NixMg1−xO band structure and the density of states demonstrate that deep Ni 3d levels are introduced into the MgO band gap, which significantly reduce the fundamental gap as confirmed by optical absorption spectra. These states broaden into a Ni 3d-derived conduction band for x > 0.074 and account for the anomalously large band gap narrowing in the NixMg1−xO solid solution system. PMID:27503808

Topological phases in (Na2O)x (P2O5)100-x glasses

NASA Astrophysics Data System (ADS)

Mohanty, Chandi; Chbeir, Ralph; Czaja, Andrew; Chen, Ping; Boolchand, Punit

We have synthesized titled glasses in the 0 <x <0.50 range of soda paying special attention to their dryness. Pure P2O5 glass was synthesized by flash evaporation of bulk powder in a quartz tube as it was pumped in several attempts, and the variation of Tg and enthalpy of relaxation (ΔHnr) measured for each attempt. These data show that as the glass got drier, Tg increased to 431°C and ΔHnr became miniscule. At higher soda content (x >20%), Tg(x) increased steadily, but with appearance of a local maximum near x = 37.5%. On the other hand ΔHnr term, revealed a Trapezoidal-like minimum in the 32.5 % <x <42.5% range, suggestive of a reversibility window or the isostatically rigid Intermediate Phase, with glasses at x >42.5% in the flexible phase while those in the 20% <x <32.5% range in the stressed rigid phase. We have also obtained Raman scattering, IR reflectance and fragility index measurements on the present glasses, and these will discussed with recent results in the field.

Infrared spectroscopy of undoped and Cu-doped (80-x)Sb{sub 2}O{sub 3}-20Li{sub 2}O-xMoO{sub 3} glasses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petkova, P., E-mail: Petya232@abv.bg; Vasilev, P.; Mustafa, M.

2016-04-21

In this work, the absorption spectra of the undoped and doped with 0.1% and 0.2% CuO{sub 2} glasses with the composition (80-x)Sb{sub 2}O{sub 3}-20Li{sub 2}O-xMoO{sub 3} are measured in the spectral region 1300-1800 nm. The optical structure of Cu{sup 2+} is investigated and the energies of the electron transitions in this metal cation are determined. The spin-orbit interaction, Lattice Compatibility Theory (LCT) analyses and the influence of molybdenum are also discussed.

Evolution of magnetic properties of CaMn1-x Nb x O3 with Nb-doping

NASA Astrophysics Data System (ADS)

Markovich, V.; Fita, I.; Wisniewski, A.; Puzniak, R.; Martin, C.; Mogilyansky, D.; Jung, G.; Gorodetsky, G.

2015-08-01

Magnetic and structural properties of Nb-doped CaMnO3 have been studied and the effect of doping with 0.02  ⩽  x  ⩽  0.1 has been investigated. Substitution of Nb5+ ion for the Mn4+ site of the parent matrix causes one-electron doping with the chemical formula \\text{CaMn}1-2x4+\\text{Mn}x3+\\text{Nb}x5+{{\\text{O}}3} , accompanied by a monotonous increase of the lattice parameters, unit-cell volume, average Mn-O bond distance and a decrease in Mn-O-Mn bond angle, with increasing x. Low temperature magnetic ground state of CaMn1-x Nb x O3 has been found to be dependent on niobium doping level. The ground magnetic state evolves from mostly antiferromagnetic, with a weak ferromagnetic component for x = 0.02-0.08, to charge ordered C-type antiferromagnetic state at x = 0.1. Spontaneous magnetization increases sharply with increasing doping level, approaches a maximal value of 4.1 emu g-1 at T = 10 K for x = 0.08, and then decreases rapidly to reach a very small value of 0.2 emu g-1 for x = 0.1. Anomalous negative magnetization behavior below the magnetic transition temperature has been observed for the compound with x = 0.04 in the field cooled magnetization and remanent dc magnetization measurements. Vertical and horizontal shifts of the hysteresis loop of the field cooled sample have been observed for CaMn0.9Nb0.1O3 as possible signatures of the exchange bias effect. The effect of hydrostatic pressure on dc magnetization for the sample with x  >  0.02 revealed a significant increase of the ferromagnetic phase volume under pressure, linked to progressive suppression of a negative magnetization in x = 0.04 sample.

Feasibility study of Fe3O4/TaO x nanoparticles as a radiosensitizer for proton therapy

NASA Astrophysics Data System (ADS)

Ahn, Sang Hee; Lee, Nohyun; Choi, Changhoon; Shin, Sung Won; Han, Youngyih; Park, Hee Chul

2018-06-01

We investigated the feasibility of using multifunctional Fe3O4/TaO x (core/shell) nanoparticles, developed for use in contrast agents for computed tomography (CT) and magnetic resonance imaging (MRI), as dose-enhancing radiosensitizers. First, to verify the detectability of Fe3O4/TaO x nanoparticles in imaging, in vivo tests were conducted. Approximately 600 mg kg‑1 of 19 nm-diameter Fe3O4/TaO x nanoparticles dispersed in phosphate-buffered saline was injected into the tail vein of six Balb/c mice used as tumour (4T1 mammary carcinoma cell) models. Three mice underwent MRI (BioSpec 70/20 USR, Bruker, Billerica, MA, USA) and micro-CT (Inveon, Siemens Preclinical, Knoxville, TN, USA) before and after the injection. The difference between the pre- and post-injection images was quantified by finding the correlation coefficient. The aorta, blood vessel, and liver were clearly seen in the MRI and micro-CT images 60 min after intravenous injection of Fe3O4/TaO x nanoparticles, but the tumour region was not visible in the CT images until after 24 h. There were large differences between the pre- and post-injection images. Second, the therapeutic enhancement dose of nanomaterials was computed via Monte Carlo simulation. Monoenergetic 70- and 150 MeV proton beams irradiated x-ray contrast agent (iodine, BaSO4), MRI contrast agent (gadolinium, Fe3O4), Au, Fe3O4/TaO x (core/shell) nanoparticles and water located at the centre of a 4  ×  4  ×  4 µm3 water phantom, upon which the dose enhancement ratio (DER) (dose with/without nanoparticles) was computed. When 70 MeV protons irradiated the Au, gadolinium, Fe3O4/TaO x , Fe3O4, iodine, and BaSO4 nanoparticles, the DERs at 1 nm were 15.76, 7.68, 7.82, 6.17, 4.85, and 5.51, respectively. Fe3O4/TaO x nanoparticles have the potential to be used as a multifunctional agent that enhances tumour detection and increases the dose. Dose enhancement with Fe3O4/TaO x was half that with Au. However, Fe3O4/TaO x is

Sputter-deposited WO x and MoO x for hole selective contacts

DOE PAGES

Bivour, Martin; Zähringer, Florian; Ndione, Paul F.; ...

2017-09-21

Here, reactive sputter deposited tungsten and molybdenum oxide (WO x, MoO x) thin films are tested for their ability to form a hole selective contact for Si wafer based solar cells. A characterization approach based on analyzing the band bending induced in the c-Si absorber and the external and implied open-circuit voltage of test structures was used. It is shown that the oxygen partial pressure allows to tailor the selectivity to some extent and that a direct correlation between induced band bending and hole selectivity exists. Although the selectivity of the sputtered films is inferior to the reference films depositedmore » by thermal evaporation, these results demonstrate a good starting point for further optimizations of sputtered WO x and MoO x towards higher work functions to improve the hole selectivity.« less

Sputter-deposited WO x and MoO x for hole selective contacts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bivour, Martin; Zähringer, Florian; Ndione, Paul F.

Here, reactive sputter deposited tungsten and molybdenum oxide (WO x, MoO x) thin films are tested for their ability to form a hole selective contact for Si wafer based solar cells. A characterization approach based on analyzing the band bending induced in the c-Si absorber and the external and implied open-circuit voltage of test structures was used. It is shown that the oxygen partial pressure allows to tailor the selectivity to some extent and that a direct correlation between induced band bending and hole selectivity exists. Although the selectivity of the sputtered films is inferior to the reference films depositedmore » by thermal evaporation, these results demonstrate a good starting point for further optimizations of sputtered WO x and MoO x towards higher work functions to improve the hole selectivity.« less

Electrical Conductivity of Cancrinite-Type Na8 - 2 x Ca x [Al6Si6O24][CO3] · 2H2O ( x ≤ 0.03) Crystals

NASA Astrophysics Data System (ADS)

Sorokin, N. I.

2018-05-01

The electrical conductivity of crystals of artificial cancrinite Na8 - 2 x Ca x [Al6Si6O24][CO3] · 2H2O ( x ≤ 0.03) has been studied in the temperature range of 498-604 K. These crystals were grown by hydrothermal synthesis on a seed in the Na2O-Al2O3-SiO2-H2O system ( t = 380-420°C, P = 3 × 107-9 × 107 Pa). The ionic conductivity of a single-crystal sample (sp. gr. P63), measured along the crystallographic axis c, is low: σ = 8 × 10-7 S/cm at 300°C. The electric transport activation energy is E a = 0.81 ± 0.05 eV. The relationship between the ionic conductivity and specific features of the atomic structure of cancrinites is discussed.

Crystal structures of K2[XSi5O12] (X = Fe2+, Co, Zn) and Rb2[XSi5O12] (X = Mn) leucites: comparison of monoclinic P21/c and Ia{\\overline 3}d polymorph structures and inverse relationship between tetrahedral cation (T = Si and X)-O bond distances and intertetrahedral T-O-T angles.

PubMed

Bell, Anthony M T; Henderson, C Michael B

2018-06-01

The leucite tectosilicate mineral analogues K 2 X 2+ Si 5 O 12 (X = Fe 2+ , Co, Zn) and Rb 2 X 2+ Si 5 O 12 (X = Mn) have been synthesized at elevated temperatures both dry at atmospheric pressure and at controlled water vapour pressure; for X = Co and Zn both dry and hydrothermally synthesized samples are available. Rietveld refinement of X-ray data for hydrothermal K 2 X 2+ Si 5 O 12 (X = Fe 2+ , Co, Zn) samples shows that they crystallize in the monoclinic space group P2 1 /c and have tetrahedral cations (Si and X) ordered onto distinct framework sites [cf. hydrothermal K 2 MgSi 5 O 12 ; Bell et al. (1994a), Acta Cryst. B50, 560-566]. Dry-synthesized K 2 X 2+ Si 5 O 12 (X = Co, Zn) and Rb 2 X 2+ Si 5 O 12 (X = Mn) samples crystallize in the cubic space group Ia{\\overline 3}d and with Si and X cations disordered in the tetrahedral framework sites as typified by dry K 2 MgSi 5 O 12 . Both structure types have tetrahedrally coordinated SiO 4 and XO 4 sharing corners to form a partially substituted silicate framework. Extraframework K + and Rb + cations occupy large channels in the framework. Structural data for the ordered samples show that mean tetrahedral Si-O and X-O bond lengths cover the ranges 1.60 Å (Si-O) to 2.24 Å (Fe 2+ -O) and show an inverse relationship with the intertetrahedral angles (T-O-T) which range from 144.7° (Si-O-Si) to 124.6° (Si-O-Fe 2+ ). For the compositions with both disordered and ordered tetrahedral cation structures (K 2 MgSi 5 O 12 , K 2 CoSi 5 O 12 , K 2 ZnSi 5 O 12 , Rb 2 MnSi 5 O 12 and Cs 2 CuSi 5 O 12 leucites) the disordered polymorphs always have larger unit-cell volumes, larger intertetrahedral T-O-T angles and smaller mean T-O distances than their isochemical ordered polymorphs. The ordered samples clearly have more flexible frameworks than the disordered structures which allow the former to undergo a greater degree of tetrahedral collapse around the interframework cavity cations. Multivariant linear regression has

Tuning Perpendicular Magnetic Anisotropy by Oxygen Octahedral Rotations in ( La 1 – x Sr x MnO 3 ) / ( SrIrO 3 ) Superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yi, Di; Flint, Charles L.; Balakrishnan, Purnima P.

Here, perpendicular magnetic anisotropy (PMA) plays a critical role in the development of spintronics, thereby demanding new strategies to control PMA. Here we demonstrate a conceptually new type of interface induced PMA that is controlled by oxygen octahedral rotation. In superlattices comprised of La 1–xSr xMnO 3 and SrIrO 3, we find that all superlattices (0 ≤ x ≤ 1) exhibit ferromagnetism despite the fact that La 1–xSr xMnO 3 is antiferromagnetic for x > 0.5. PMA as high as 4 × 10 6 erg/cm 3 is observed by increasing x and attributed to a decrease of oxygen octahedral rotationmore » at interfaces. We also demonstrate that oxygen octahedral deformation cannot explain the trend in PMA. These results reveal a new degree of freedom to control PMA, enabling discovery of emergent magnetic textures and topological phenomena.« less

Tuning Perpendicular Magnetic Anisotropy by Oxygen Octahedral Rotations in ( La 1 – x Sr x MnO 3 ) / ( SrIrO 3 ) Superlattices

DOE PAGES

Yi, Di; Flint, Charles L.; Balakrishnan, Purnima P.; ...

2017-08-14

Here, perpendicular magnetic anisotropy (PMA) plays a critical role in the development of spintronics, thereby demanding new strategies to control PMA. Here we demonstrate a conceptually new type of interface induced PMA that is controlled by oxygen octahedral rotation. In superlattices comprised of La 1–xSr xMnO 3 and SrIrO 3, we find that all superlattices (0 ≤ x ≤ 1) exhibit ferromagnetism despite the fact that La 1–xSr xMnO 3 is antiferromagnetic for x > 0.5. PMA as high as 4 × 10 6 erg/cm 3 is observed by increasing x and attributed to a decrease of oxygen octahedral rotationmore » at interfaces. We also demonstrate that oxygen octahedral deformation cannot explain the trend in PMA. These results reveal a new degree of freedom to control PMA, enabling discovery of emergent magnetic textures and topological phenomena.« less

A Raman scattering study of the structural ordering in Bi1- x La x FeO3 ceramic ferroelectromagnetics

NASA Astrophysics Data System (ADS)

Teplyakova, N. A.; Titov, S. V.; Verbenko, I. A.; Sidorov, N. V.; Reznichenko, L. A.

2015-09-01

Based on Raman spectra, we have studied structural ordering processes in ceramics of ferroelectromagnetics Bi1- x La x FeO3 ( x = 0.075-0.20). It has been found that the structure of Bi1- x La x FeO3 is close to the structure of the crystal BiFeO3. However, lines in Raman spectra of Bi1- x La x FeO3 are considerably broadened compared to lines in the Raman spectrum of the BiFeO3 single crystal, which indicates that the structure of solid solutions is much more disordered. In Raman spectra of Bi1- x La x FeO3, in the range of librational vibrations of octahedra as a whole (50-90 cm-1), several groups of lines are observed in frequency ranges 59-69, 72-77, and 86-92 cm-1 (depending on the composition of solid solution). This confirms X-ray data that examined solid solutions are not single-phase. At a La content x = 0.120, Raman lines in the low-frequency spectral range narrow, which indicates that the ordering of structural units in cationic sublattices somewhat increases. Upon an increase in the content of La in the Bi1- x La x FeO3 structure, no unambiguous dependence of parameters of spectral lines is observed. It is likely that this is explained by the fact that, as the value of x increases, the character of the incorporation of La into the structure of the solid solution changes.

Structural and thermoelectric properties of n-type Sr1- x Ti x MnO3- δ perovskite system

NASA Astrophysics Data System (ADS)

Kim, C. M.; Seo, J. W.; Choi, S.-M.; Seo, W.-S.; Lee, S.; Lim, Y. S.; Park, K.

2015-03-01

A series of Sr1- x Ti x MnO3- δ (0.05 ≤ x ≤ 0.3) was fabricated by the solid-state reaction method. We studied the structural and thermoelectric properties of Sr1- x Ti x MnO3- δ , with respect to the partial substitution of Ti4+ for Sr2+. The sintered Sr1- x Ti x MnO3- δ crystallized in the hexagonal perovskite-type structure with a space group of P6 3 / mmc. For x ≤ 0.1, the partial substitution of Ti4+ for Sr2+ led to increases in the electrical conductivity and the absolute value of the Seebeck coefficient, thus enhancing the power factor. The highest power factor (2.5 × 10-5 Wm-1K-2) was obtained for Sr0.9Ti0.1MnO3- δ at 800°C. The partial substitution of Ti4+ for Sr2+ in SrMnO3- δ led to a significant improvement in the thermoelectric properties. [Figure not available: see fulltext.

Thermoelectric Properties of LaFePO1-xFx and LaFeAsO1-xFx ---Possibility of the Hidden Mass Enhancement of LaFeAsO1-xFx---

NASA Astrophysics Data System (ADS)

Okuda, Tetsuji; Hirata, Wataru; Takemori, Akira; Suzuki, Shinnosuke; Saijo, Satoshi; Miyasaka, Shigeki; Tajima, Setsuko

2011-04-01

We investigated thermoelectric properties for polycrystalline oxypnictide LaFePO1-xFx and LaFeAsO1-xFx. The temperature (T) and F-doping dependences of resistivity (ρ) and Seebeck coefficient (S) are quite different between these compounds. In contrast to a monotonic T dependence and an absence of large F-doping dependences of ρ and S for LaFePO1-xFx, the S for LaFeAsO1-xFx for 0O0.89F0.11. The non-monotonic behavior of S with the relatively large absolute value and the reported T dependence of Hall coefficient for LaFeAsO1-xFx seem to evidence an instability of an orbital order accompanying a stripe-type AF order even in the over F-doping region for LaFeAsO1-xFx and indicate a possibility of a hidden mass enhancement of LaFeAsO1-xFx.

Synthesis and characterization of (1-x)Bi(Mg{sub 2/3}Sb{sub 1/3})O{sub 3}-xPbTiO{sub 3} piezoceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Upadhyay, Ashutosh; Dwivedi, Saurabh; Pandey, Rishikesh

2016-05-23

We present here the comprehensive x-ray diffraction and polarization-electric field hysteresis studies on (1-x)Bi(Mg{sub 2/3}Sb{sub 1/3})O{sub 3}-xPbTiO{sub 3} piezoceramics with x = 0.52, 0.56 and 0.60. The powder x-ray diffraction data reveals the presence of tetragonal phase for all the compositions. The saturation of hysteresis loop is observed for x ≤ 0.56.

Luminescence in microcrystalline green emitting Li2Mg1-xZrO4:xTb3+ (0.1 ≤ x ≤ 2.0) phosphor

NASA Astrophysics Data System (ADS)

Panse, V. R.; Kokode, N. S.; Shinde, K. N.; Dhoble, S. J.

2018-03-01

Green emitting Li2Mg1-xZrO4:xTb3+ (0.1 ≤ x ≤ 2.0) phosphor powders were synthesized via the wet chemical synthesis and the luminescent proprieties were studied when excited at 380 nm and present a dominant and strong green luminescence peak at 543 nm, due to D-F transition. The preparation of Li2Mg1-xZrO4:xTb3+ (0.1 ≤ x ≤ 2.0) phosphor powders were confirmed by X-ray diffraction (XRD) results without any secondary or impurity phases. The size and morphology of the Li2Mg1-xZrO4:xTb3+ (0.1 ≤ x ≤ 2.0) phosphor powders were further examined by scanning electron microscopy (SEM). Photoluminescence (PL) results have shown strongest green emission at 543 nm, which is originated due to 5D4-7F5 transition of Tb3+ ion, for the Li2Mg1-xZrO4:xTb3+ (0.1 ≤ x ≤ 2.0) phosphor. The addition of concentration Tb3+ was greatly improved the photoluminescence properties of present phosphors. The present study suggests that the Li2Mg1-xZrO4:xTb3+ (0.1 ≤ x ≤ 2.0) phosphor is a strong candidate as a green component for phosphor-converted white light-emitting diodes (LEDs).

Tuning Perpendicular Magnetic Anisotropy by Oxygen Octahedral Rotations in ( La 1 - x Sr x MnO 3 ) / ( SrIrO 3 ) Superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yi, Di; Flint, Charles L.; Balakrishnan, Purnima P.

Perpendicular magnetic anisotropy (PMA) plays a critical role in the development of spintronics, thereby demanding new strategies to control PMA. Here we demonstrate a conceptually new type of interface induced PMA that is controlled by oxygen octahedral rotation. In superlattices comprised of La1-xSrxMnO3 and SrIrO3, we find that all superlattices (0<=x<=1) exhibit ferromagnetism despite the fact that La1-xSrxMnO3 is antiferromagnetic for x>0.5. PMA as high as 4×10^6 erg/cm^3 is observed by increasing x and attributed to a decrease of oxygen octahedral rotation at interfaces. We also demonstrate that oxygen octahedral deformation cannot explain the trend in PMA. These results revealmore » a new degree of freedom to control PMA, enabling discovery of emergent magnetic textures and topological phenomena.« less

Effects of H3O+, OH-, \\text{O}_{2}^{-} , \\text{NO}_{\\text{x}}^{-} and NO x for Escherichia coli inactivation in atmospheric pressure DC corona discharges

NASA Astrophysics Data System (ADS)

Sekimoto, Kanako; Gonda, Rena; Takayama, Mitsuo

2015-08-01

The effects of ionic and neutral species such as H3O+, OH-, \\text{O}2- , \\text{NO}x- (x = 2, 3), and NO x on Escherichia coli (E. coli) inactivation in gas and liquid phases was investigated using atmospheric pressure DC corona discharges with point-to-plane electrodes. The above chemical species as well as OH and O3 were selectively irradiated onto E. coli suspensions on agar plates using a needle angle of 45° with respect to the plates, airflow, and a grid plate. Irradiation with the positive ion H3O+ did not inactivate E. coli, while the negative ions OH-/\\text{O}2- resulted in bactericidal inactivation, in both gas and liquid phases. In contrast, the negative ions \\text{NO}x- and neutral species NO x in the gas phase had quite strong bactericidal effects on E. coli compared to those species in the liquid phase. These results suggest that liquid-phase HNO3, formed primarily via the reaction of gas-phase \\text{NO}x- and NO x with H2O in agar, has only a weak inactivation effect on E. coli. Furthermore, using naphthylethylenediamine spectrophotometry, the threshold amount of gas-phase \\text{NO}x- and NO x for E. coli inactivation was determined to be  ≈1.3   ×   10-9 mol mm-1.

Optical properties of nanocrystalline potassium lithium niobate in the glass system (100-x) TeO2-x(1.5K2O-Li2O-2.5Nb2O5).

PubMed

Ahamad, M Niyaz; Varma, K B R

2009-08-01

Optically clear glasses of various compositions in the system (100-x) TeO2-x(1.5K2O-Li2O-2.5Nb2O5) (2 < or = x < or = 12, in molar ratio) were prepared by the melt-quenching technique. The glassy nature of the as-quenched samples was established via differential scanning calorimetry (DSC). The amorphous and the crystalline nature of the as-quenched and heat-treated samples were confirmed by the X-ray powder diffraction and transmission electron microscopic (TEM) studies. Transparent glasses comprising potassium lithium niobate (K3Li2Nb5O15) microcrystallites on the surface and nanocrystallites within the glass were obtained by controlled heat-treatment of the as-quenched glasses just above the glass transition temperature (T(g)). The optical transmission spectra of these glasses and glass-crystal composites of various compositions were recorded in the 200-2500 nm wavelength range. Various optical parameters such as optical band gap, Urbach energy, refractive index were determined. Second order optical non-linearity was established in the heat-treated samples by employing the Maker-Fringe method.

Structural and ferroelectric phase evolution in [KNbO3]1-x[BaNi1/2Nb1/2O3 -δ] x (x =0 ,0.1 )

NASA Astrophysics Data System (ADS)

Hawley, Christopher J.; Wu, Liyan; Xiao, Geoffrey; Grinberg, Ilya; Rappe, Andrew M.; Davies, Peter K.; Spanier, Jonathan E.

2017-08-01

The phase transition evolution for [KNbO3]1-x[BaNi1/2Nb1/2O3 -δ] x(x =0 ,0.1 ) is determined via complementary dielectric permittivity and Raman-scattering measurements. Raman scattering by optical phonons over the range of 100-1000 cm-1 for 83 K x =0.1 and compared with those for end member x =0 and with the results of temperature-dependent dielectric permittivity. Rigorous peak fitting analyses of spectra collected from the solid solution and end member indicate structural and ferroelectric phase transition temperatures that are close to those for the KNbO3 end member despite the inclusion of 5 atomic % of ferroelectrically inactive Ni cations. Density functional theory calculations were performed in the solid solution and end member using both cation displacement and Berry phase-based methods. Differences in the electronic and polar properties between the solid solution and the end member highlights local and nonlocal characteristics, which are discussed in relation to the experimental data.

Structural variations and dielectric properties of (Bi1-xL ax ) 2Si O5 (0 ≤x ≤0.1 ): Polycrystallines synthesized by crystallization of Bi-Si-O and Bi-La-Si-O glasses

NASA Astrophysics Data System (ADS)

Taniguchi, Hiroki; Tatewaki, Shingo; Yasui, Shintaro; Fujii, Yasuhiro; Yamaura, Jun-ichi; Terasaki, Ichiro

2018-04-01

This paper focuses on effects of isovalent La substitution on the crystal structure and dielectric properties of ferroelectric B i2Si O5 . Polycrystalline samples of (Bi1-xL ax ) 2Si O5 are synthesized by crystallization of Bi-Si-O and Bi-La-Si-O glasses with a composition range of 0 ≤x ≤0.1 . The crystal structure changes from monoclinic to tetragonal with increasing La-substitution rate x at room temperature. This structural variation stems from the change in orientation of Si O4 tetrahedra that form one-dimensional chains when they are in the ordered configuration, thus suggesting that lone-pair electrons play an important role in sustaining one-dimensional chains of Si O4 tetrahedra. Synchronizing with the disordering of Si O4 chains, ferroelectric phase transition temperature of (Bi1-xL ax ) 2Si O5 sharply decreases as x increases, and ferroelectricity finally vanishes at around x =0.03 . The present results demonstrate that lone-pair electrons of Bi play an important role in the ferroelectricity of B i2Si O5 through propping the ordered structure of one-dimensional Si O4 chains with stereochemical activity. Furthermore, an additional phase transition has been first discovered in the low-temperature region of (Bi1-xL ax ) 2Si O5 with x ≤0.01 , where the ordered one-dimensional Si O4 chains remain.

Dielectric properties and phase transition behaviors in (1-x)PbZrO3-xPb(Mg1/2W1/2)O3 ceramics

NASA Astrophysics Data System (ADS)

Vittayakorn, Naratip; Charoonsuk, Piyanut; Kasiansin, Panisara; Wirunchit, Supamas; Boonchom, Banjong

2009-09-01

The solid solution of lead zirconate [PbZrO3 (PZ)] and lead magnesium tungstate [Pb(Mg1/2W1/2)O3 (PMW)] has been synthesized by the wolframite precursor method. The crystal structure, phase transformations, dielectric and thermal properties of (1-x)PZ-xPMW, where x =0.00-0.10, were investigated. The crystal structure of sintered ceramics was analyzed by x-ray diffraction. Phase-pure perovskite was obtained for all compositions. Furthermore, a change from orthorhombic to rhombohedral symmetry was observed as the mole fraction of increased PMW. As a result, it was found that PbZrO3-Pb(Mg1/2W1/2)O3 undergoes successive transitions from the antiferroelectric phase to the ferroelectric phase to the paraelectric state. The coexistence of orthorhombic and rhombohedral phases in this binary system is located near the composition x =0.1.

Modifying Optical Properties of ZnO Films by Forming Zn[subscript 1-x] Co[subscript x]O Solid Solutions via Spray Pyrolysis

ERIC Educational Resources Information Center

Bentley, Anne K.; Weaver, Gabriela C.; Russell, Cianan B.; Fornes, William L.; Choi, Kyoung-Shin; Shih, Susan M.

2007-01-01

A simple and cost-effective experiment for the development and characterization of semiconductors using Uv-vis spectroscopy is described. The study shows that the optical properties of ZnO films can be easily modified by forming Zn[subscript 1-x] Co[subscript x]O solid solutions via spray pyrolysis.

Preparation, electronic structure, and chemical bonding of lead-free (1 - x)(K0.5Bi0.5)TiO3- xBaTiO3 solid solution

NASA Astrophysics Data System (ADS)

Sasikumar, S.; Saravanan, R.; Saravanakumar, S.; Robert, M. Charles

2018-01-01

Polycrystalline lead-free (1 - x)(K0.5Bi0.5)TiO3- xBaTiO3, ((1 - x)KBT- xBT) ( x = 0.00, 0.08, 0.12) ceramics were synthesized via solid-state reaction method. The powder X-ray diffraction (PXRD) and structural refinement results confirm that a single-phase tetragonal structure with space group P4mm. Charge density distribution inside the unit cell of (1 - x)KBT- xBT was investigated by the maximum entropy method. Charge density analysis reveals the reduction in ionic nature along K/Bi-O bond and enhancement of covalent nature along Ti-O bond with the addition of BaTiO3. The charge density distribution studies done using maximum entropy method for (1 - x)KBT- xBT have not been done so far. The surface morphology study was done using scanning electron microscopy (SEM). Energy dispersive X-rays spectra (EDS) were used to investigate the elemental compositions present in the system. The dielectric constant and loss tangent were studied as a function of frequency. The dielectric constant and loss were decreased with increase of frequency. Room temperature dielectric constant ( ɛ) and loss (tan δ) were measured for x = 0.00 about 511 and 0.51, respectively, at a frequency of 10 kHz.

High-Temperature Thermoelectric Properties of (1 - x) SrTiO3 - ( x) La1/3NbO3 Ceramic Solid Solution

NASA Astrophysics Data System (ADS)

Srivastava, Deepanshu; Azough, F.; Molinari, M.; Parker, S. C.; Freer, R.

2015-06-01

Ceramics based on SrTiO3 are of growing interest as thermoelectric materials because of their high-temperature stability and non-toxicity. Substitution of La and Nb into the perovskite structure provides opportunities to control both the microstructure and properties. Ceramic solid solutions of (1 - x) SrTiO3 - ( x) La1/3NbO3 were prepared by the mixed oxide route, using compositional steps of x = 0.1. Pressed pellets were sintered at temperatures of 1573 K to 1723 K in air. Addition of aliovalent ions (La3+, Nb5+) on the A/B sites (Sr2+, Ti4+) led to A-Site cation deficiency in the stoichiometric compositions and other defect structures which increased carrier concentration. A maximum ZT of 0.004 was obtained for the x = 0.2 stoichiometric sample, although much higher ZT values are possible by sample reduction.

Structure and radiation effect of Er-stuffed pyrochlore Er2(Ti2-xErx)O7-x/2 (x = 0-0.667)

NASA Astrophysics Data System (ADS)

Yang, D. Y.; Xu, C. P.; Fu, E. G.; Wen, J.; Liu, C. G.; Zhang, K. Q.; Wang, Y. Q.; Li, Y. H.

2015-08-01

Er-stuffed pyrochlore series Er2(Ti2-xErx)O7-x/2 (x = 0, 0.162, 0.286, 0.424 and 0.667) were synthesized using conventional ceramic processing procedures. The structure of Er2(Ti2-xErx)O7-x/2 is effectively tailored by the Er stuffing level (x). In order to study the radiation effect of Er-stuffed pyrochlores, irradiation experiments were performed with 400 keV Ne2+ ions to fluences ranging from 5 × 1014 to 3.0 × 1015 ions/cm2 at cryogenic condition. Irradiation induced microstructural evolution was examined using a grazing incidence X-ray diffraction technique. It is found that the irradiated layer of Er2(Ti2-xErx)O7-x/2 undergoes significant lattice disordering and swelling at fluences of ⩽1.5 × 1015 ions/cm2 and amorphization at fluences of ⩾1.5 × 1015 ions/cm2. The radiation effect depends strongly on the chemical compositions of the samples. Both the lattice swelling percentage and the amorphous fraction decrease with increasing x. The experimental results are discussed in the context of cation antisite defect. The defect formation energy which varies as a function of x is responsible for the difference in the structural behaviors of Er2(Ti2-xErx)O7-x/2 under 400 keV Ne2+ ion irradiation.

Nanocrystalline Ce 1- xY xO 2- x/2 (0≤ x≤0.35) Oxides via Carbonate Precipitation: Synthesis and Characterization

NASA Astrophysics Data System (ADS)

Li, Ji-Guang; Ikegami, Takayasu; Wang, Yarong; Mori, Toshiyuki

2002-10-01

A novel carbonate (co)precipitation method, employing nitrates as the starting salts and ammonium carbonate as the precipitant, has been used to synthesize nanocrystalline CeO 2 and Ce 1- xY xO 2- x/2 ( x≤0.35) solid-solutions. The resultant powders are characterized by elemental analysis, differential thermal analysis/thermogravimetry (DTA/TG), X-ray diffractometry (XRD), Brunauer-Emmett-Teller (BET) analysis, and high-resolution scanning electron microscopy (HRSEM). Due to the direct formation of carbonate solid-solutions during precipitation, Ce 1- xY xO 2- x/2 solid-solution oxides are formed directly during calcination at a very low temperature of ˜300°C for 2 h. The thus-produced oxide nanopowders are essentially non-agglomerated, as revealed by BET in conjunction with XRD analysis. The solubility of YO 1.5 in CeO 2 is determined via XRD to be somewhere in the range from 27 to 35 mol%, from which a Y 2O 3-related type-C phase appears in the final product. Y 3+-doping promotes the formation of spherical nanoparticles, retards thermal decomposition of the precursors, and suppresses significantly crystallite coarsening of the oxides during calcination. The activation energy for crystallite coarsening increases gradually from 68.7 kJ mol -1 for pure CeO 2 to 138.6 kJ mol -1 for CeO 2 doped with 35 mol% YO 1.5. The dopant effects on crystallite coarsening is elaborated from the view point of solid-state chemistry.

Structural studies of TiC{sub 1−x}O{sub x} solid solution by Rietveld refinement and first-principles calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Bo, E-mail: youqin5912@yahoo.com.cn; Hou, Na; Huang, Shanyan

2013-08-15

The lattice parameters, structural stability and electronic structure of titanium oxycarbides (TiC{sub 1−x}O{sub x}, 0≤x≤1) solid solution were investigated by Rietveld refinement and first-principles calculations. Series of TiC{sub 1−x}O{sub x} were precisely synthesized by sintering process under the vacuum. Rietveld refinement results of XRD patterns show the properties of continuous solid solution in TiC{sub 1−x}O{sub x} over the whole composition range. The lattice parameters vary from 0.4324 nm to 0.4194 nm decreasing with increasing oxygen concentration. Results of first-principles calculations reveal that the disorder C/O structure is stable than the order C/O structure. Further investigations of the vacancy in Ti{submore » 1−Va}(C{sub 1−x}O{sub x}){sub 1−Va} solid solution present that the structure of vacancy segregated in TiO-part is more stable than the disorder C/O structure, which can be ascribed to the Ti–Ti bond across O-vacancy and the charge redistributed around Ti-vacancy via the analysis of the electron density difference plots and PDOS. - Graphical abstract: XRD of series of titanium oxycarbides (TiC{sub 1−x}O{sub x}, 0≤x≤1) solid solution prepared by adjusting the proportion of TiO in the starting material. Highlights: • Titanium oxycarbides were obtained by sintering TiO and TiC under carefully controlled conditions. • Rietveld refinement results show continuous solid solution with FCC structure in TiC{sub 1−x}O{sub x}. • The disorder C/O structure is stable than the order C/O structure. • Introduction of vacancy segregated in TiO-part is more stable than disorder C/O structure. • Ti–Ti bond across O-vacancy and the charge redistributed around Ti-vacancy enhance structural stability.« less

C60 and U ion irradiation of Gd 2Ti xZr 2-xO 7 pyrochlore

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jiaming; Toulemonde, Marcel; Lang, Maik

2015-08-01

Gd 2Ti xZr 2-xO 7 (x = 0 to 2) pyrochlore was irradiated by 30 MeV C 60 clusters, which provide an extremely high ionizing energy density. Here, high-resolution transmission electron microscopy revealed a complex ion-track structure in Gd 2Ti 2O 7 and Gd 2TiZrO 7, consisting of an amorphous core and a shell of a disordered, defect-fluorite structure.

Syntheses and luminescence study for La{sub 1−x}Eu{sub x}[B{sub 5}O{sub 8}(OH){sub 2}]·1.5H{sub 2}O (0≤x≤0.40) and the dehydrated products β-La{sub 1−x}Eu{sub x}B{sub 5}O{sub 9} (0≤x≤0.15)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xiaorui; Zhou, Zhengyang; Yang, Haixia

La{sub 1−x}Eu{sub x}[B{sub 5}O{sub 8}(OH){sub 2}]·1.5H{sub 2}O with the Eu{sup 3+}-doping upper limit of 40 atom% were synthesized hydrothermally. Thereafter, thermal treatments at 710 °C were applied to obtain β-La{sub 1−x}Eu{sub x}B{sub 5}O{sub 9}. The solid solution range is even narrower, i.e. 0≤x≤0.15, due to the mismatch between La{sup 3+} and Eu{sup 3+}. The host borate system shows a typical concentration quenching effect at x=0.20 under CT excitation, and this is postponed to x=0.30 under the f−f excitation. β-La{sub 1−x}Eu{sub x}B{sub 5}O{sub 9} shows a very intense absorption of charge transfer, and gives strong red emissions at 615 nm withmore » large R/O ratios (1.9–2.4). The saturation effect appears at x=0.11, which is probably due to the lattice distortion. Eu{sup 3+} luminescence was applied as the structural probe to study the local coordination environment change during the dehydration and re-crystallization processes of La{sub 0.93}Eu{sub 0.07}[B{sub 5}O{sub 8}(OH){sub 2}]·1.5H{sub 2}O. - Highlights: • La{sub 1−x}Eu{sub x}[B{sub 5}O{sub 8}(OH){sub 2}]·1.5H{sub 2}O (0≤x≤0.40) were prepared by hydrothermal method. • The Eu{sup 3+}-doping limit in β-La{sub 1−x}Eu{sub x}B{sub 5}O{sub 9} is 15 atom% proved by powder XRD. • La{sub 1−x}Eu{sub x}[B{sub 5}O{sub 8}(OH){sub 2}]·1.5H{sub 2}O show relatively weaker red emissions. • β-La{sub 1−x}Eu{sub x}B{sub 5}O{sub 9} shows an intense CT absorption together with strong red emissions. • Eu{sup 3+} luminescence was studied when annealing La{sub 0.93}Eu{sub 0.07}[B{sub 5}O{sub 8}(OH){sub 2}]·1.5H{sub 2}O.« less

Magnetic impurities in conducting oxides. II. (Sr1-xLax)(Ru1-xCox)O3 system

NASA Astrophysics Data System (ADS)

Mamchik, A.; Dmowski, W.; Egami, T.; Chen, I.-Wei

2004-09-01

The perovskite solid solution between ferromagnetic SrRuO3 and antiferromagnetic LaCoO3 is studied and its structural, electronic,and magnetic properties are compared with (Sr1-xLax)(Ru1-xFex)O3 . The lower 3d energy levels of Co3+ cause a local charge transfer from 4dRu4+ , a reaction that has the novel feature of being sensitive to the local atomic structure such as cation order. Despite such a complication, Co , like Fe , spin-polarizes the itinerant electrons in SrRuO3 to form a large local magnetic moment that is switchable at high fields. In the spin glass regime when Anderson localization dominates, a large negative magnetoresistance emerges as a result of spin polarization of mobile electronic carriers that occupy states beyond the mobility edge. A phenomenological model predicting an inverse relation between magnetoresistance and saturation magnetization is proposed to explain the composition dependence of magnetoresistance for both (Sr1-xLax)(Ru1-xCOx)O3 and (Sr1-xLax)(Ru1-xFex)O3 systems.

Relation of Giant Thermo-EMF, Magnetothermo-EMF, Magnetoresistance, and Magnetization to Magnetic Impurity States in Manganites Nd(1- x)Sr x MnO3 and Sm(1- x)Sr x MnO3

NASA Astrophysics Data System (ADS)

Koroleva, L. I.; Batashev, I. K.; Morozov, A. S.; Balbashov, A. M.; Szymczak, H.; Slawska-Waniew, A.

2018-02-01

Thermo-EMF, magnetothermo-EMF, magnetoresistance, and magnetization of single-crystal samples of Nd(1- x)Sr x MnO3 and Sm(1- x)Sr x MnO3 with 0 ≤ x ≤ 0.3 have been studied experimentally. A sharp increase in the thermo-EMF and giant magnetothermo-EMF and magnetoresistance has been observed near the Curie point T C in compounds with 0.15 ≤ x ≤ 0.3. At the same time, no peculiarities have been found in compositions with x = 0. Since compounds with x > 0 consist of ferromagnetic clusters of the ferron type that reside in an antiferromagnetic A-type matrix, this means that the sharp increase in the thermo-EMF near T C is caused by ferrons. Indeed, the disappearance of ferrons due to a magnetic field or heating above T C leads to an abrupt decrease in the thermo-EMF. Therefore, thermo-EMF in alloyed magnetic semiconductors has been determined by the impurity concentration and the sample volume.

Positron lifetime studies of defect structures in Ba(1-x)K(x)BiO3

NASA Astrophysics Data System (ADS)

Obrien, J. C.; Howell, R. H.; Radousky, H. B.; Sterne, P. A.; Hinks, D. G.; Folkerts, T. J.; Shelton, R. N.

1990-12-01

Temperature-dependent positron lifetime experiments have been performed from room temperature to cryogenic temperatures on Ba(1-x)K(x)BiO3, for x = 0.4 and 0.5. From the temperature dependence of the positron lifetime in the normal state, we observe a clear signature of competition between separate defect populations to trap the positron. Theoretical calculations of lifetimes of free or trapped positrons have been performed on Ba(1-x)K(x)BiO3, to help identify these defects. Lifetime measurements separated by long times have been performed and evidence of aging effects in the sample defect populations is seen in these materials.

Critical current density in (YBa2Cu3O7-δ)1-x-(PrBa2Cu3O7-δ)x melt-textured composites

NASA Astrophysics Data System (ADS)

Opata, Yuri Aparecido; Monteiro, João Frederico Haas Leandro; Jurelo, Alcione Roberto; Siqueira, Ezequiel Costa

2018-06-01

Melt textured (YBa2Cu3O7-δ)1-x-(PrBa2Cu3O7-δ)x composites (x = 0.00 and x = 0.05) were grown using the top seeding method. The effect of the PrBa2Cu3O7-δ phase on the growth process and the modification of the microstructure as well as on the physical properties was analyzed. X-ray analyses indicated that both pure and Pr-doped samples present an orthorhombic superconducting phase. From resistivity measurements for YBa2Cu3O7-δ and (YBa2Cu3O7-δ)0.95-(PrBa2Cu3O7-δ)0.05 samples, the Tcab did not change and was around 90.5 K. However, from magnetic measurements, the superconductivity was observed in critical temperatures TC = 92.9 K and 92.4 K for YBa2Cu3O7-δ and (YBa2Cu3O7-δ)0.95-(PrBa2Cu3O7-δ)0.05 samples, respectively. The YBa2Cu3O7-δ sample showed higher critical current densities than those shown by the (YBa2Cu3O7-δ)0.95-(PrBa2Cu3O7-δ)0.05 sample, with values of JC = 5.85 × 105 A/cm2 and 4.72 × 105 A/cm2, respectively. This paper also discusses the importance of Pr substitution on nano- and micro-meter scales to enhance JC(H).

Electrical conduction mechanism of LaNi{sub x}Me{sub 1−x}O{sub 3−δ} (Me = Fe, Mn)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Niwa, Eiki, E-mail: e-niwa@phys.chs.nihon-u.ac.jp; Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences, Nihon University, Setagaya-ku, Tokyo 156-8550; Maeda, Hiroki

Graphical abstract: Compositional dependence of (a) electrical conductivity and (b) E{sub a} for hopping conduction of LaNi{sub x}Me{sub 1−x}O{sub 3} (Me = Fe, Mn). - Highlights: • Electrical conduction mechanism of LaNi{sub x}Me{sub 1−x}O{sub 3} (Me = Fe, Mn) was investigated. • Hopping conduction model could be applied for conductivity of both specimens. • The difference of E{sub a} due to that of energy level of Fe and Mn was observed. • Hole concentration estimated by iodimetry increases with increasing Ni content. - Abstract: Electrical conduction mechanism of LaNi{sub x}Fe{sub 1−x}O{sub 3−δ} and LaNi{sub x}Mn{sub 1−x}O{sub 3+δ} expected as Sr-freemore » new cathode material for solid oxide fuel cells was analyzed. Electrical conduction behaviors of both specimens could be well fitted by small polaron hopping conduction model. The electrical conductivity of LaNi{sub x}Fe{sub 1−x}O{sub 3−δ} increased with increasing Ni content, showing agreement with decrease of activation energy for hopping conduction. The decrease of electrical conductivity and increase of activation energy of LaNi{sub x}Mn{sub 1−x}O{sub 3+δ} were observed with increasing Ni content for 0.0 ≤ x ≤ 0.4. Further Ni substitution increased electrical conductivity and decreased activation energy for 0.4 ≤ x ≤ 0.6. It was revealed using iodometry that the difference of hole carrier density between LaNi{sub x}Fe{sub 1−x}O{sub 3−δ} and LaNi{sub x}Mn{sub 1−x}O{sub 3+δ} was small. It was suspected that the origin of the difference of electrical conduction behavior of LaNi{sub x}Fe{sub 1−x}O{sub 3−δ} and LaNi{sub x}Mn{sub 1-x}O{sub 3+δ} was difference of energy level of e{sub g} band composed of Fe 3d or Mn 3d orbitals and their overlapping quantity with O 2p and Ni 3d band.« less

Enhanced dielectric and piezoelectric responses in Zn 1 -xMg xO thin films near the phase separation boundary

DOE PAGES

Kang, Xiaoyu; Shetty, Smitha; Garten, Lauren; ...

2017-01-23

Dielectric and piezoelectric properties for Zn 1-xMg xO (ZMO) thin films are reported as a function of MgO composition up to and including the phase separation region. Zn 1-xMg xO (0.25 ≤ x ≤ 0.5) thin films with c-axis textures were deposited by pulsed laser deposition on platinized sapphire substrates. The films were phase pure wurtzite for MgO concentrations up to 40%; above that limit, a second phase with rocksalt structure evolves with strong {100} texture. With increasing MgO concentration, the out-of-plane ( d33,f) and in-plane ( e31,f) piezoelectric coefficients increase by 360% and 290%, respectively. The increase in piezoelectricmore » coefficients is accompanied by a 35% increase in relative permittivity. Loss tangent values fall monotonically with increasing MgO concentration, reaching a minimum of 0.001 for x ≥ 0.30, at which point the band gap is reported to be 4 eV. As a result, the enhanced piezoelectric response, the large band gap, and the low dielectric loss make Zn 1-xMg xO an interesting candidate for thin film piezoelectric devices, and demonstrate that compositional phase transformations provide opportunities for property engineering.« less

Tuning of magnetism in DyMn1-xFexO3 (x<0.1) system by iron substitution

NASA Astrophysics Data System (ADS)

Mihalik, Matúš; Mihalik, Marián; Zentková, Mária; Uhlířová, Klára; Kratochvílová, Marie; Fitta, Magdalena; Quintero, Pedro A.; Meisel, Mark W.

2018-05-01

The effect of Fe doping on the magnetism of DyMn1-xFexO3 (x<0.1) single crystals is reported. Specifically, TN of the Mn sublattice decreases from 38 K (x = 0) to 33 K (x = 0.1), TS = 17.9 K (x = 0) connected with the transition of Mn-spins into the cycloidal magnetic phase decreases to 15.9 K (x = 0.01) and vanishes for higher x concentrations, while the ordering temperature of the Dy sublattice varies between 5.9 K (x = 0.01) and 4.1 K (x = 0.02). These results indicate the ground state magnetic structure of DyMnO3 can be destabilized, and the multiferroicity is completely suppressed by very low Fe doping. Similar effects were previously observed in the multiferroic TbMn1-xFexO3 system.

Composition-dependent surface chemistry of colloidal Ba xSr 1-xTiO 3 perovskite nanocrystals

DOE PAGES

Margossian, Tigran; Culver, Sean P.; Larmier, Kim; ...

2016-11-01

Ba xSr 1-xTiO 3 perovskite nanocrystals, prepared by the vapor diffusion sol-gel method and characterized by state of the art surface techniques, display significantly different O-H stretching frequencies and adsorption properties towards CO 2 as a function of the alkaline earth composition (Ba vs. Sr). Lastly, the difference of properties can be associated with the more basic nature of BaO-rich than SrO-rich surfaces.

Metal-insulator transition in Nd(1-x)Eu(x)NiO(3) compounds.

PubMed

Escote, M T; Barbeta, V B; Jardim, R F; Campo, J

2006-07-05

Polycrystalline Nd(1-x)Eu(x)NiO(3) (0≤x≤0.5) compounds were synthesized in order to investigate the character of the metal-insulator (MI) phase transition in this series. Samples were prepared through the sol-gel route and subjected to heat treatments at ∼1000 °C under oxygen pressures as high as 80 bar. X-ray diffraction (XRD) and neutron powder diffraction (NPD), electrical resistivity ρ(T), and magnetization M(T) measurements were performed on these compounds. The NPD and XRD results indicated that the samples crystallize in an orthorhombic distorted perovskite structure, space group Pbnm. The analysis of the structural parameters revealed a sudden and small expansion of ∼0.2% of the unit cell volume when electronic localization occurs. This expansion was attributed to a small increase of ∼0.003 Å of the average Ni-O distance and a simultaneous decrease of ∼-0.5° of the Ni-O-Ni superexchange angle. The ρ(T) measurements revealed a MI transition occurring at temperatures ranging from T(MI)∼193 to 336 K for samples with x = 0 and 0.50, respectively. These measurements also show a large thermal hysteresis in NdNiO(3) during heating and cooling processes, suggesting a first-order character of the phase transition at T(MI). The width of this thermal hysteresis was found to decrease appreciably for the sample Nd(0.7)Eu(0.3)NiO(3). The results indicate that cation disorder associated with increasing substitution of Nd by Eu is responsible for changing the first-order character of the transition in NdNiO(3).

Thermal Conductivity and Expansion Coefficient of (Sm1- x Yb x )2Ce2O7 Ceramics for Thermal Barrier Coatings

NASA Astrophysics Data System (ADS)

Xiaoge, Chen; Hongsong, Zhang; Kun, Sun; Xudan, Dang; Haoming, Zhang; Bo, Ren; An, Tang

2017-12-01

In the current paper, the (Sm1- x Yb x )2Ce2O7 ceramics were prepared via sol-gel and high-temperature solid reaction methods. The phase composition, microstructure, thermal conductivity, and expansion coefficient were investigated. Results indicate that pure (Sm1- x Yb x )2Ce2O7 ceramics with single defect-fluorite structure are synthesized successfully. Owing to the phonon scattering caused by Yb addition, the thermal conductivity of (Sm1- x Yb x )2Ce2O7 ceramics decreases with increasing Yb2O3 content at identical temperatures, which is lower than that of YSZ. Due to the relatively low ionic radius of Yb3+ ions, the addition of Yb2O3 decreases the thermal expansion coefficient of (Sm1- x Yb x )2Ce2O7 ceramics, which is higher than that of 8YSZ. The synthesized (Sm1- x Yb x )2Ce2O7 ceramics can be explored as candidate materials for thermal barrier coatings.

Repositioning Trends of Latina/o/x Student Enrollments in Community Colleges

ERIC Educational Resources Information Center

Zerquera, Desiree D.; Acevedo-Gil, Nancy; Flores, Elizabeth; Marantal, Patrick

2018-01-01

This study used descriptive statistics to complicate the national narrative of Latina/o/x student college-going trends and aims to provide directions for future research on Latina/o/x students in the community college. Taking a state-by-state perspective, this study examined whether Latina/o/x college students enrolled in community colleges at…

Influence of oxygen vacancies in ALD HfO2-x thin films on non-volatile resistive switching phenomena with a Ti/HfO2-x/Pt structure

NASA Astrophysics Data System (ADS)

Sokolov, Andrey Sergeevich; Jeon, Yu-Rim; Kim, Sohyeon; Ku, Boncheol; Lim, Donghwan; Han, Hoonhee; Chae, Myeong Gyoon; Lee, Jaeho; Ha, Beom Gil; Choi, Changhwan

2018-03-01

We report a modulation of oxygen vacancies profile in atomic layer deposition (ALD) HfO2-x thin films by reducing oxidant pulse time (0.7 s-0.1 s) and study its effect on resistive switching behavior with a Ti/HfO2-x/Pt structure. Hf 4f spectra of x-ray photoelectron microscopy (XPS) and depth profile confirm varied oxygen vacancies profiles by shifts of binding energies of Hf 4f5/2 and Hf 4f7/2 main peaks and its according HfO2-x sub-oxides for each device. The ultraviolet photoelectron spectroscopy (UPS) confirms different electron affinity (χ) of HfO2 and HfO2-x thin films, implying that barrier height at Ti/oxide interface is reduced. Current transport mechanism is dictated by Ohmic conduction in fully oxidized HfO2 thin films - Device A (0.7 s) and by Trap Filled Space Charge Limited Conduction (TF-SCLC) in less oxidized HfO2-x thin films - Device B (0.3 s) and Device C (0.1 s). A switching mechanism related to the oxygen vacancies modulation in Ti/HfO2-x/Pt based resistive random access memory (RRAM) devices is used to explain carefully notified current transport mechanism variations from device-to-device. A proper endurance and long-time retention characteristics of the devices are also obtained.

Thermoelectric properties of the ceramic oxide Sr1- x La x TiO3

NASA Astrophysics Data System (ADS)

Mahmud, Iqbal; Yoon, Man-Soon; Kim, Il-Ho; Choi, Moon-Kwan; Ur, Soon-Chul

2016-01-01

The effect of lanthanum on the electric and the thermoelectric properties of the ceramic oxide Sr1- x La x TiO3 (where x = 0.0, 0.04, 0.06, 0.08 and 0.12 mole) have been studied. La-doped SrTiO3 was prepared by using the conventional mixed-oxide reaction method. XRD patterns indicated that almost all the La atoms incorporated into the SrTiO3 crystal provided charge carriers. The lattice parameter increases with increasing La doping content. The relative densities of all the samples varied from 89.6% to 94.8%. The electrical conductivity increased with La doping up to 0.08 moles and then decreased as the content of La was increased above 0.08 moles. The thermal conductivity decreased with increasing La content. The largest absolute value of the Seebeck coefficient, 394 μVK-1 at 973 K, was observed at x = 0.04. The Sr0.92La0.08TiO3 sample showed its maximum electrical conductivity at 773 K and its largest ZT value of 0.20 at 973 K.

The dielectric behavior of Zn1-xNixO/NiO two-phase composites

NASA Astrophysics Data System (ADS)

Joshi, D. C.; Thota, S.; Nayak, S.; Harish, D. D.; Mahesh, P.; Kumar, A.; Pamu, D.; Qureshi, Md

2014-10-01

The effect of nickel content on the dielectric permittivity ‘ɛr’ and the ac-electrical conductivity of Zn1-xNixO/NiO (0 ≤ x ≤ 0.55) two-phase composites were investigated. The antiferro to the paramagnetic Néel temperature TN (~ 523 K) of the NiO associated with the structural phase transition from the rhombohedral to the cubic phase has been exploited to realize a dielectric anomaly across 523-541 K in the Zn1-xNixO/NiO composite system. Also, a giant dielectric peak across 410 °C in pure NiO was observed together with an anomaly across TN. The formation of tiny polar clusters due to the compositional heterogeneity for the samples with x ≥ 0.16 drove the system to exhibit a weakly coupled relaxor-like behavior with a locally varying maximum temperature of T* (~ 530 K at 106 Hz), obeying the Vogel-Fulcher law and the Uchino-Nomura criteria. The values of the diffuseness-exponent ‘γ’ (1.91) and the shape-parameter ‘δ’ (88 °C) were determined by using the empirical scaling relation (ɛA/ɛr = 1 + 0.5 (T - TA)2/ δ2), which is often used to describe relaxor-like behavior. Our results provide strong evidence for the variable-range-hopping of charge carriers between the localized states. The effects of non-ohmic sample-electrode contact impedance and negative-capacitance on the global dielectric behavior of a Zn1-xNixO/NiO composite system are discussed.

Magnetic polarons in antiferromagnetic CaMnO3-x (x<0.01) probed by O17 NMR

NASA Astrophysics Data System (ADS)

Trokiner, A.; Verkhovskii, S.; Yakubovskii, A.; Gerashenko, A.; Monod, P.; Kumagai, K.; Mikhalev, K.; Buzlukov, A.; Litvinova, Z.; Gorbenko, O.; Kaul, A.; Kartavtzeva, M.

2009-06-01

We study with O17 NMR and bulk magnetization a lightly electron doped CaMnO3-x (x<0.01) polycrystalline sample in the G -type antiferromagnetic state. The O17 NMR spectra show two lines with very different intensities corresponding to oxygen sites with very different local magnetic environments. The more intense unshifted line is due to the antiferromagnetic (AF) matrix. The thermal dependence of the magnetic moment of the AF sublattice deduced from the O17 linewidth is typical of insulating three-dimensional Heisenberg antiferromagnets. The less intense, strongly shifted line directly evidences the existence of ferromagnetic (FM) domains embedded in the AF spin lattice. The extremely narrow line in zero magnetic field indicates a nearly perfect alignment of the manganese spins in the FM domains which also display an unusually weak temperature dependence of their magnetic moment. We show that these FM entities start to move above 40 K in a slow-diffusion regime. These static and dynamic properties bear a strong similarity with those of a small size self-trapped magnetic polaron.

Structural and dielectric properties of Zn1-xAlxO nanoparticles

NASA Astrophysics Data System (ADS)

Giri, N.; Mondal, A.; Sarkar, S.; Ray, R.

2018-05-01

Aluminium doped ZnO (AZO) nano-crystalline sample has been synthesized using chemical precipitation method with different doping concentrations. Detailed structural and morphological investigations of Zn1-xAlxO have been carried out using X-ray diffraction (XRD) and FE-SEM, respectively. Dependence of grain size of AZO with dopant concentration has been studied. Ac conductivity, dielectric constant and dielectric loss of Zn1-xAlxO (0 ≤ x ≤ 0.1) are investigated as a function of frequency (ω) and doping concentration (x) at room temperature.

Characterization of thin films of the solid electrolyte Li(x)Mg(1-2x)Al(2+x)O4 (x = 0, 0.05, 0.15, 0.25).

PubMed

Put, Brecht; Vereecken, Philippe M; Mees, Maarten J; Rosciano, Fabio; Radu, Iuliana P; Stesmans, Andre

2015-11-21

RF-sputtered thin films of spinel Li(x)Mg(1-2x)Al(2+x)O4 were investigated for use as solid electrolyte. The usage of this material can enable the fabrication of a lattice matched battery stack, which is predicted to lead to superior battery performance. Spinel Li(x)Mg(1-2x)Al(2+x)O4 thin films, with stoichiometry (x) ranging between 0 and 0.25, were formed after a crystallization anneal as shown by X-ray diffraction and transmission electron microscopy. The stoichiometry of the films was evaluated by elastic recoil detection and Rutherford backscattering and found to be slightly aluminum rich. The excellent electronic insulation properties were confirmed by both current-voltage measurements as well as by copper plating tests. The electrochemical stability window of the material was probed using cyclic voltammetry. Lithium plating and stripping was observed together with the formation of a Li-Pt alloy, indicating that Li-ions passed through the film. This observation contradicted with impedance measurements at open circuit potential, which showed no apparent Li-ion conductivity of the film. Impedance spectroscopy as a function of potential showed the occurrence of Li-ion intercalation into the Li(x)Mg(1-2x)Al(2+x)O4 layers. When incorporating Li-ions in the material the ionic conductivity can be increased by 3 orders of magnitude. Therefore it is anticipated that the response of Li(x)Mg(1-2x)Al(2+x)O4 is more adequate for a buffer layer than as the solid electrolyte.

Interface energetics and atomic structure of epitaxial La{sub 1−x}Sr{sub x}CoO{sub 3} on Nb:SrTiO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Overmeere, Quentin, E-mail: quentin.vanovermeere@uclouvain.be, E-mail: john.d.baniecki@jp.fujitsu.com; Baniecki, John D., E-mail: quentin.vanovermeere@uclouvain.be, E-mail: john.d.baniecki@jp.fujitsu.com; Yamazaki, Takashi

2015-06-15

The energetics at oxide semiconductor/La{sub 1−x}Sr{sub x}CoO{sub 3} heterojunctions, including the respective alignment of the valence and conduction bands, govern charge transfer and have to be determined for the design of future La{sub 1−x}Sr{sub x}CoO{sub 3}-based devices. In this letter, the electronic and atomic structures of epitaxial La{sub 1−x}Sr{sub x}CoO{sub 3} on Nb-doped strontium titanate are revealed by scanning transmission electron microscopy, electron energy loss spectroscopy, and in situ x-ray and ultra violet photoelectron spectroscopies. For LaCoO{sub 3}, a valence band (VB) offset of 2.8 ± 0.1 eV is deduced. The large offset is attributed to the orbital contributions of the Co 3dmore » states to the VB maximum of the LaCoO{sub 3} thin films, with no evidence of interface dipole contributions. The sensitivity of the valence band orbital character to spin state ordering and oxygen vacancies is assessed using density functional theory.« less

X-ray and dielectric characterization of Co doped tetragonal BaTiO3 ceramics

NASA Astrophysics Data System (ADS)

Bujakiewicz-Koronska, R.; Vasylechko, L.; Markiewicz, E.; Nalecz, D. M.; Kalvane, A.

2017-01-01

The crystal structure modifications of BaTiO3 induced by cobalt doping were studied. The polycrystalline (1 - x)BaTiO3 + xCo2O3 samples, with x ≤ 10 wt.%, were prepared by high temperature sintering conventional method. According to X-ray phase and structural characterization, performed by full-profile Rietveld refinement technique, all synthesized samples showed tetragonal symmetry perovskite structure with minor amount of parasitic phases. Pure single-phase composition has been detected only in the low level of doping BaTiO3. It was indicated that substitution of Co for the Ti sites in the (1 - x)BaTiO3 + xCo2O3 series led to decrease of tetragonality (c/a) of the BaTiO3 perovskite structure. This effect almost vanished in the (1 - x)BaTiO3 + xCo2O3 samples with nominal Co content higher than ∼1 wt.%, in which precipitation of parasitic Co-containing phases CoO and Co2TiO4 has been observed. Based on the results, the solubility limit of Co in Ti sub-lattice in the (1 - x)BaTiO3 + xCo2O3 series is estimated as x = 0.75 wt.%.

Modulation-Doped SrTiO3/SrTi1-xZrxO3 Heterostructures

NASA Astrophysics Data System (ADS)

Kajdos, Adam Paul

Two-dimensional electron gases (2DEGs) in SrTiO3 have attracted considerable attention for exhibiting a variety of interesting physical phenomena, such as superconductivity and magnetism. So far, most of the literature has focused on interfaces between nonpolar SrTiO3 and polar perovskite oxides (e.g. LaAlO3 or rare-earth titanates), where high carrier density 2DEGs (˜3 x 1014 cm-2) are generated by polar discontinuity. Modulation doping is an alternative approach to generating a 2DEG that has been explored extensively in III-V semiconductors but has not heretofore been explored in complex oxides. This approach involves interfacing an undoped semiconductor with a doped semiconductor whose conduction band edge lies at a higher energy, which results in electrons diffusing into the undoped semiconductor transport channel, where scattering from ionized dopants is minimized. Realizing a high-mobility modulation-doped structure with a SrTiO3 transport channel therefore requires both the optimization of the transport channel by minimizing native defects as well as the development of a perovskite oxide which has a suitable band offset with SrTiO3 and can be electron-doped. The growth of high electron mobility SrTiO3 as a suitable transport channel material was previously demonstrated using the hybrid molecular beam epitaxy (MBE) approach, where Sr is delivered via a solid source and Ti is delivered using a metal-organic precursor, titanium (IV) tetra-isopropoxide (TTIP). Expanding on this, in-situ reflection high-energy electron diffraction (RHEED) is used to track the surface and resulting film cation stoichiometry of homoepitaxial SrTiO3 (001) thin films grown by hybrid MBE. It is shown that films with lattice parameters identical to bulk single-crystal substrates within the detection limit of high-resolution X-ray diffraction (XRD) measurements exhibit an evolution in surface reconstruction with increasing TTIP beam-equivalent pressure. The change in the observed

LiAl xCo 1- xO 2 as 4 V cathodes for lithium ion batteries

NASA Astrophysics Data System (ADS)

Huang, Haitao; Rao, G. V. Subba; Chowdari, B. V. R.

Nominal LiAl xCo 1- xO 2 with x ranging from 0.1 to 0.3 was prepared by heating mixture of Al(OH) 3, Co 3O 4 and LiOH at 750°C in air. The effect of substitution of non-transition metal, Al, in LiCoO 2 is investigated as a 4 V cathode for lithium ion. X-ray diffraction (XRD) indicates formation of a single phase (R3¯m) within this range of substitution. When cycled between 4.5 and 2.5 V vs. Li/Li + at a current density of 1 mA cm -2, the LiAl 0.15Co 0.85O 2 cathode exhibits reversible capacity of 160 mA h g -1 initially. XRD of the cathode made at the end of 10 cycles reveals no significant change on host structure.

Influence of Ce Doping on Structural and Transport Properties of Ca1- x Ce x MnO3 ( x=0.2) Manganite

NASA Astrophysics Data System (ADS)

Varshney, Dinesh; Mansuri, Irfan

2011-01-01

We have investigated structural, electric, magnetic and thermal transport properties of electron doped Ca1- x Ce x MnO3 ( x=0.2) manganites. The Cerium substitution for Ca2+causes electron doping into insulating CaMnO3 without e g electron. At room temperature the polycrystalline Ca0.8Ce0.2MnO3 is in the crystallographic orthorhombic structure, with Pnma space group symmetry from the refinement of x-ray powder diffraction patterns. The electrical resistivity data infers that Ca0.8Ce0.2MnO3 manganite is in the semiconducting phase. A smooth linear behavior of log plot values is obtained and is well fitted with adiabatic small polaron conduction model. Nearest-neighbor hopping of a small polaron leads to a mobility with a thermally activated form. The negative values of thermopower infer electron as carriers in Ca0.8Ce0.2MnO3. From susceptibility measurements the Ce doped CaMnO3 shows a transition from antiferromagnetic (AFM) to paramagnetic (PM) phase.

Impedance and magnetoelectric characteristics of (1 - x)BaTiO3- xLa0.7Sr0.3MnO3 ( x = 0.1 and 0.3) nano-composites

NASA Astrophysics Data System (ADS)

Nayek, C.; Murugavel, P.; Dinesh Kumar, S.; Subramanian, V.

2015-08-01

We have synthesized the phase-pure (1 - x)BaTiO3- xLa0.7Sr0.3MnO3 ( x = 0.1 and 0.3) magnetoelectric composites without interdiffusion among the existing phases. The magnetic measurements revealed an anomaly at the ferroelectric Curie temperature (393 K) of BaTiO3, and the dielectric data revealed an anomaly at the ferromagnetic transition temperature (360 K) of La0.7Sr0.3MnO3 ascertaining the magnetoelectric coupling in the composite. Impedance analysis indicated dipolar polarization contributions to the dielectric spectrum with two non-Debye-type relaxations. Both the grain and grain boundary contributions were present in the system with dominant grain boundary effect in all the composites. The composites show semiconducting behavior with the barrier hopping-type conducting mechanism. To avoid the free charge carrier and the space charge contributions, the magnetoelectric response was measured at high frequency range. The maximum values of magnetoelectric voltage coefficient measured at 100 kHz were 221 and 219 mV/Oe-cm for x = 0.1 and 0.3 samples, respectively.

The effects of starting materials in the synthesis of (Ga(1-x)Znx)(N(1-x)O(x)) solid solution on its photocatalytic activity for overall water splitting under visible light.

PubMed

Hisatomi, Takashi; Maeda, Kazuhiko; Lu, Daling; Domen, Kazunari

2009-01-01

The influence of starting materials on the physicochemical and photocatalytic properties of (Ga(1-x)Zn(x))(N(1-x)O(x)) were investigated in an attempt to optimize the preparation conditions. The catalyst was successfully prepared by nitriding a starting mixture of ZnO and Ga2O3. A mixture of metallic zinc and GaN, however, did not afford the desired compound. The crystallinity, surface area, composition, and absorption characteristics of the resultant (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution are found to be dependent on the morphology of ZnO but largely insensitive to the choice of Ga2O3 polymorph. The use of coarser-grained ZnO results in a coarser-grained catalyst with elevated zinc and oxygen content and reduced uniformity in composition and crystallinity. The results demonstrate the importance of selecting appropriate ZnO and Ga2O3 starting materials for maximizing the photocatalytic activity of (Ga(1-x)Zn(x))(N(1-x)O(x)) for overall water splitting under visible light.

Preparation, Structural and Dielectric Behaviors of CoxMn1-xMn2O4 (0 ≤ x ≤ 1) Nanoparticles

NASA Astrophysics Data System (ADS)

Taufiq, A.; Muzammil, M.; Fuad, A.; Hidayat, N.; Sunaryono, S.; Mufti, N.; Hidayat, A.; Diantoro, M.; Munasir, M.

2018-05-01

Cobalt-manganese oxide nanoparticles become remarkable metal oxides due to their physical characters, for example, their electrical properties. In this paper, we report the synthesis of Co x Mn1-x Mn2O4 (0 ≤ x ≤ 1) nanoparticles via a precipitation method. The structural and dielectric properties were investigated by means of X-ray diffractometer (XRD) and LCR-meter. From the data analysis, it was found that the Co x Mn1-x Mn2O4 particles structured spinel cubic with the particle size ranging from 22.7 to 28.6 nm. Increasing Co2+ ions led to declining lattice and crystal volume of the Co x Mn1-x Mn2O4 nanoparticles. Such phenomenon was originated from the substitution process of Co2+ ions that change the metal construction both at the octahedral and tetrahedral sites. Furthermore, the Co2+ ion substitution resulted in an increase in the dielectric properties of the Co x Mn1-x Mn2O4 nanoparticles regarding with dipole moment. Interestingly, the increase was also influenced by reducing the particle size and crystal volume of the Co x Mn1-x Mn2O4 nanoparticles.

Optical evidence for the spin-state disorder in LaCo1-x Rh x O3

NASA Astrophysics Data System (ADS)

Terasaki, Ichiro; Asai, Shinichiro; Taniguchi, Hiroki; Okazaki, Ryuji; Yasui, Yukio; Ikemoto, Yuka; Moriwaki, Taro

2017-06-01

We have measured the infrared reflectivity of single-crystalline samples of LaCo1-x Rh x O3 (x  =  0, 0.05 and 0.10) from 10 to 300 K from 0.05 to 0.15 eV. We find that the optical phonons of the Co-O stretching mode depend on temperature and the Rh content. Analysis with three Lorentz oscillators reveals that the spin state of Co3+ in LaCo1-x Rh x O3 can be understood in terms of a solid solution of low-spin- and high-spin-state Co3+ ions, and the substituted Rh ion retains some fraction of the high-spin Co3+ ions down to low temperature.

New process of preparation, X-ray characterisation, structure and vibrational studies of a solid solution LiTiOAs 1-xP xO 4 (0⩽ x⩽1)

NASA Astrophysics Data System (ADS)

Chakir, M.; El Jazouli, A.; Chaminade, J. P.; Bouree, F.; de Waal, D.

2006-01-01

LiTiOAs 1-xP xO 4 (0⩽ x⩽1) compounds have been prepared using solutions of Li, Ti, As and P elements as starting products. Selected compositions have been investigated by powder X-ray or neutrons diffraction analysis, Raman and infrared spectroscopy. The structure of LiTiOAs 1-xP xO 4 ( x=0, 0.5 and 1) samples determined by Rietveld analysis is orthorhombic with Pnma space group. It is formed by a 3D network of TiO 6 octahedra and XO 4 ( X=As 1-xP x) tetrahedra where octahedral cavities are occupied by lithium atoms. TiO 6 octahedra are linked together by corners and form infinite chains along a-axis. Ti atoms are displaced from the centre of octahedral units in alternating short (1.700-1.709 Å) and long (2.301-2.275 Å) Ti-O bonds. Raman and infrared studies confirm the existence of Ti-O-Ti chains. Thermal stability of LiTiOAsO 4 has been reported.

Enhanced ferromagnetic order in Sr{sub 4}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} featuring canted [MnO{sub 4}]{sub ∞} spin chains of mixed-valent Mn(III)/Mn(IV). Aliovalent substitution of the Sr{sub 4−x}Ln{sub x}Mn{sup III}{sub 2+x}Mn{sup IV}{sub 1−x}O{sub 3}(GeO{sub 4}){sub 3} solid-solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, J. Palmer; Sulejmanovic, Dino; Becht, Gregory

2013-10-15

Crystals of Sr{sub 4−x}Ln{sub x}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} (x=0; x∼0.15 for Ln=La, Pr, Nd, Sm. Eu, Gd, Dy; x∼0.3 for Ln=Gd) were isolated upon using high-temperature, solid-state methods in molten-salt media. These compounds are isostructural with the previously reported Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3} (Ln=La, Sm, Gd) series that contains the same [MnO{sub 4}]{sub ∞} spin chains. The synthesis of the Sr{sub 4}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} (x=0) phase was carried out by a double aliovalent substitution with respect to the Sr{sup 2+} and Ge{sup 4+} ions that replace Na{sup +}/Ln{sup 3+} and As{sup 5+} in Na{sub 3}LnMn{submore » 3}O{sub 3}(AsO{sub 4}){sub 3}, respectively. The title series contains mixed-valent Mn(III)/Mn(IV) and shows a limited range of solid solution, both of which were not observed in the previously reported Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3} series. To form the Sr{sub 4−x}Ln{sub x}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} solid solution, one of the Sr{sup 2+} sites, i.e., the original Ln-site in Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3}, is partially substituted by Ln{sup 3+} in a statistical disorder of Sr{sub 1−x}/Ln{sub x}. Initial magnetic investigations of selected derivatives reveal higher ferromagnetic ordering temperatures than those reported for the Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3} series, presumably attributed to a lesser degree of canting as a result of introducing non-Jahn–Teller Mn{sup 4+} ions. Also intriguing is the observation of multiple anomalies at low temperatures which appear to be of electronic origins. - Graphical abstract: Sr{sub 4−x}Ln{sub x}Mn(III){sub 2+x}Mn(IV){sub 1−x}O{sub 3}(GeO{sub 4}){sub 3}. Display Omitted - Highlights: • Double aliovalent substitution: Sr{sub 4}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} with respect to Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3}. • Solid solution with respect to statistical disorder of Sr{sub 1−x

Luminescent properties of Cr-doped (GdX, Y1-X)3Al5O12 infra-red scintillator crystals

NASA Astrophysics Data System (ADS)

Suzuki, Akira; Kurosawa, Shunsuke; Yamaji, Akihiro; Shoji, Yasuhiro; Pejchal, Jan; Kamada, Kei; Yokota, Yuui; Yoshikawa, Akira

2014-10-01

Cr-doped (GdX Y1-X)3Al5O12 (X = 0, 0.25, 0.50) crystals prepared by the micro-pulling down method were investigated to develop a infra-red scintillator for implantable patient dosimeter in radiation therapy. In order to evaluate their optical and scintillation performance, the following properties were measured: (i) transmittance between ultra-violet and near-infra red region, (ii) photoluminescence spectra under Xe-lamp excitation, and (iii) X-ray excited radio-luminescence spectra. Cr:Y3Al5O12 and Cr:(Gd0.25 Y0.75)3Al5O12 crystals showed increased transmittance of 80%, while Cr:(Gd0.50 Y0.50)3Al5O12 had a lower transmittance of 40% due to its polycrystalline structure. In addition, all the Cr:(GdX Y1-X)3Al5O12 crystals showed sharp scintillation luminescence peaks ascribed to Cr3+ d-d transitions. Therefore, these results suggested that Cr:Y3Al5O12 and Cr:(Gd0.25 Y0.75)3Al5O12 crystals can be candidate materials for the dosimeter use.

New Findings on the Phase Transitions in Li(sub 1-x)CoO(sub 2) and Li(sub 1-x)NiO(sub 2) Cathode Materials During Cycling: In Situ Synchrotron X-Ray Diffraction Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, X. Q.; Sun, X.; McBreen, J.

The authors have utilized synchrotron x-ray radiation to perform ''in situ'' x-ray diffraction studies on Li{sub 1-x}CoO{sub 2} and Li{sub 1-x}NiO{sub 2} cathodes. A C/10 charging rate was used for a Li/Li{sub 1-x}CoO{sub 2} cell. For the Li/Li{sub 1-x}NiO{sub 2} cells, C/13 and C/84 rates were applied. The in situ XRD data were collected during the first charge from 3.5 to 5.2 V. For the Li{sub 1-x}CoO{sub 2} cathode, in the composition range of x = 0 to x = 0.5, a new intermediate phase H2a was observed in addition to the two expected hexagonal phases H1 and H2. Inmore » the region very close to x = 0.5, some spectral signatures for the formation of a monoclinic phase M1 were also observed. Further, in the x = 0.8 to x = 1 region, the formation of a CdI{sub 2} type hexagonal phase has been confirmed. However, this new phase is transformed from a CdCl{sub 2} type hexagonal phase, rather than from a monoclinic phase M2 as previously reported in the literature. For the Li{sub 1-x}NiO{sub 2} system, by taking the advantage of the high resolution in 2{theta} angles through the synchrotron based XRD technique, they were able to identify a two-phase coexistence region of hexagonal phase H1 and H2, which has been mistakenly indexed as a single phase region for monoclinic phase M1. Interesting similarities and differences between these two systems are also discussed.« less

Impact of AlO x layer on resistive switching characteristics and device-to-device uniformity of bilayered HfO x -based resistive random access memory devices

NASA Astrophysics Data System (ADS)

Chuang, Kai-Chi; Chung, Hao-Tung; Chu, Chi-Yan; Luo, Jun-Dao; Li, Wei-Shuo; Li, Yi-Shao; Cheng, Huang-Chung

2018-06-01

An AlO x layer was deposited on HfO x , and bilayered dielectric films were found to confine the formation locations of conductive filaments (CFs) during the forming process and then improve device-to-device uniformity. In addition, the Ti interposing layer was also adopted to facilitate the formation of oxygen vacancies. As a result, the resistive random access memory (RRAM) device with TiN/Ti/AlO x (1 nm)/HfO x (6 nm)/TiN stack layers demonstrated excellent device-to-device uniformity although it achieved slightly larger resistive switching characteristics, which were forming voltage (V Forming) of 2.08 V, set voltage (V Set) of 1.96 V, and reset voltage (V Reset) of ‑1.02 V, than the device with TiN/Ti/HfO x (6 nm)/TiN stack layers. However, the device with a thicker 2-nm-thick AlO x layer showed worse uniformity than the 1-nm-thick one. It was attributed to the increased oxygen atomic percentage in the bilayered dielectric films of the 2-nm-thick one. The difference in oxygen content showed that there would be less oxygen vacancies to form CFs. Therefore, the random growth of CFs would become severe and the device-to-device uniformity would degrade.

Simultaneous multi-wavelength ultraviolet excited single-phase white light emitting phosphor Ba1-x(Zr,Ti)Si3O9:xEu

NASA Astrophysics Data System (ADS)

Zhou, Zhenzhen; Liu, Guanghui; Ni, Jia; Liu, Wanlu; Liu, Qian

2018-05-01

A kind of novel compound Ba1-x(Zr,Ti)Si3O9:xEu simultaneously activated by different-valence Eu2+ and Eu3+ ions has been successfully synthesized. The existence of Ti4+-O2- charge transfer (CT) transitions in Ba1-xZrSi3O9:xEu is proved by the photoluminescence spectra and first principle calculations, and the Ti4+ ions come from the impurities in commercial ZrO2 raw materials. Under the excitation of multi-wavelength ultraviolet radiation (λEX = 392, 260, 180 nm), Ba1-xZrSi3O9:xEu (x = 0.15) can directly emit nearly white light. The coexistence of multiple luminescent centers and the energy transfer among Zr4+-O2- CT state, Ti4+-O2- CT state, Eu2+ and Eu3+ ions play important roles in the white light emission. Ba1-xZrSi3O9:xEu (x = 0.15) has good thermal stability, in particular, the intensity of emission spectrum (λEX = 392 nm) at 150 °C is ∼96% of that at room temperature. In general, the multi-wavelength ultraviolet-excited single-phase white light emitting phosphor Ba1-x(Zr,Ti)Si3O9:xEu possesses a promise for applications in white light emitting diodes (WLEDs), agriculture, medicine and other photonic fields.

Thermal behaviour of GdCo1-xMnxO3 cobaltates

NASA Astrophysics Data System (ADS)

Thakur, Rasna; Thakur, Rajesh K.; Gaur, N. K.

2018-05-01

With the objective of exploring the unknown thermodynamic behavior of GdCo1-xMnxO3 family, we present here an investigation of the temperature-dependent (10K≤T≤1000K) thermodynamic properties of GdCo1-xMnxO3 (x=0.1 to 0.8). The specific heat of GdCoO3 with Mn doping in the perovskite structure at B-site has been studied by means of a Modified Rigid Ion Model (MRIM). The cohesive energy, specific heat (C), volume thermal expansion (α) and Gruneisen parameter (γ) of GdCo1-xMnxO3 compounds are also discussed.

Structure, magnetic, and electrical properties of Zn1-xMnxO material

NASA Astrophysics Data System (ADS)

Sebayang, P.; Hulu, S. F.; Nasruddin, Aryanto, D.; Kurniawan, C.; Subhan, A.; Sudiro, T.; Ginting, M.

2017-07-01

ZnO and MnO2 powder were synthesized using solid state reaction method to produce Zn1-xMnxO materials. Effect of dopant concentrations at the material of Zn1-xMnxO (x = 0.015, 0.02, 0.025) to the change of crystal structure, electrical and magnetic properties was studied. The X-ray diffraction (XRD) result of the samples that were doped with Mn showed a hexagonal wurtzite polycrystalline structure. The addition of Mn dopant resulting the decrease of lattice parameters and peaks intensity. The significant increase of the peak intensity occurred at x = 0.02, which also indicated an increase in the crystal quality of ZnO. The change of the ZnO structure affected the electrical and magnetic properties of the samples.

The magnetic and adsorption properties of ZnO1-xSx nanoparticles.

PubMed

Zhang, Huiyun; Liu, Guixian; Cao, Yanqiang; Chen, Jing; Shen, Kai; Kumar, Ashwini; Xu, Mingxiang; Li, Qi; Xu, Qingyu

2017-10-11

Sulfur is easy to be incorporated into ZnO nanoparticles by the solution-combustion method. Herein, the magnetic and adsorption properties of a series of ZnO 1-x S x (x = 0, 0.05, 0.1, 0.15, and 0.2) nanoparticles were systematically investigated. The X-ray diffraction patterns show that the as-prepared ZnO 1-x S x nanoparticles have the hexagonal wurtzite structure of ZnO with a low sulfur content that gradually transforms into the zinc blende structure of ZnS when the x value is greater than 0.1. PL spectra show several bands due to different transitions, which have been explained by the recombination of free excitons or defect-induced transitions. The introduction of sulfur not only modifies the bandgap of ZnO, but also impacts the concentration of Zn vacancies. The as-prepared ZnO shows weak room-temperature ferromagnetism, and the incorporation of sulfur improves the ferromagnetism owing to the increased concentration of Zn vacancies, which may be stabilized by the doped sulfur ions. The adsorption capability of ZnO 1-x S x nanoparticles has been significantly improved, and the process can be well described by the pseudo-first-order kinetic model and the Freundlich isotherm model. The mechanism has been confirmed to be due to the active sulfate groups existing in zinc oxysulfide nanoparticles.

Study of concentration-dependent cobalt ion doping of TiO2 and TiO(2-x)Nx at the nanoscale.

PubMed

Gole, James L; Prokes, Sharka M; Glembocki, O J; Wang, Junwei; Qiu, Xiaofeng; Burda, Clemens

2010-07-01

Experiments with a porous sol-gel generated TiO(2) nanocolloid and its corresponding oxynitride TiO(2-x)N(x) are carried out to evaluate those transformations which accompany additional doping with transition metals. In this study, doping with cobalt (Co(ii)) ions is evaluated using a combination of core level and VB-photoelectron and optical spectroscopy, complementing data obtained from Raman spectroscopy. Raman spectroscopy suggests that cobalt doping of porous sol-gel generated anatase TiO(2) and nitridated TiO(2-x)N(x) introduces a spinel-like structure into the TiO(2) and TiO(2-x)N(x) lattices. TEM and XPS data complemented by valence band-photoelectron spectra demonstrate that metallic cobalt clusters are not formed even at high doping levels. As evidenced by Raman spectroscopy, the creation of a spinel-like structure is commensurate with the room temperature conversion of the oxide and its oxynitride from the anatase to the rutile form. The onset of this kinetically driven process correlates with the formation of spinel sites within the TiO(2) and TiO(2-x)N(x) particles. Despite their visible light absorption, the photocatalytic activity of these cobalt seeded systems is diminished relative to the oxynitride TiO(2-x)N(x).

Enhanced Photocatalytic Activity in Bi1-x Ba x FeO3 Prepared by a PEG400 Assisted Sol-Gel Method

NASA Astrophysics Data System (ADS)

Zhang, Chenlan; Chen, Jianguo; Jin, Dengren; Cheng, Jinrong

2018-03-01

Ferroelectric Bi1-x Ba x FeO3 nanoparticles for x = 0, 0.01, 0.03, 0.05 and 0.10 were synthesized by a polyethylene glycol 400 (PEG400) assisted sol-gel method. X-ray diffraction reveals that Bi1-x Ba x FeO3 nanoparticles exhibit a distorted rhombohedral structure with the R3c space group, and the diffraction peaks shift upon incorporation of Ba. Transmission electron microscope analysis shows that the particle size of Bi1-x Ba x FeO3 nanoparticles is in the range of 30-60 nm, decreasing with an increase in Ba content. Bi1-x Ba x FeO3 nanoparticles have band gaps in the range of 1.68-2.0 eV, which are capable of responding to visible light irradiation. The rate of the photocatalytic degradation of Bi1-x Ba x FeO3 nanoparticles for x = 0.03 to methyl orange (MO) dye achieves about 81% under visible light irradiation for 3 h, which is higher than that of 66% for pure phase BiFeO3 (BFO). Moreover, the effects of Ba2+ modification on the band gap of BFO crystallites have been investigated and discussed.

Energetics of a uranothorite (Th 1–xU xSiO 4) solid solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Xiaofeng; Szenknect, Stephanie; Mesbah, Adel

High-temperature oxide melt solution calorimetric measurements were completed to determine the enthalpies of formation of the uranothorite, (USiO 4) x–(ThSiO 4) 1–x, solid solution. Phase-pure samples with x values of 0, 0.11, 0.21, 0.35, 0.71, and 0.84 were prepared, purified, and characterized by powder X-ray diffraction, electron probe microanalysis, thermogravimetric analysis and differential scanning calorimetry coupled with in situ mass spectrometry, and high-temperature oxide melt solution calorimetry. This work confirms the energetic metastability of coffinite, USiO 4, and U-rich intermediate silicate phases with respect to a mixture of binary oxides. Furthermore, variations in unit cell parameters and negative excess volumesmore » of mixing, coupled with strongly exothermic enthalpies of mixing in the solid solution, suggest short-range cation ordering that can stabilize intermediate compositions, especially near x = 0.5.« less

Energetics of a uranothorite (Th 1–xU xSiO 4) solid solution

DOE PAGES

Guo, Xiaofeng; Szenknect, Stephanie; Mesbah, Adel; ...

2016-10-11

High-temperature oxide melt solution calorimetric measurements were completed to determine the enthalpies of formation of the uranothorite, (USiO 4) x–(ThSiO 4) 1–x, solid solution. Phase-pure samples with x values of 0, 0.11, 0.21, 0.35, 0.71, and 0.84 were prepared, purified, and characterized by powder X-ray diffraction, electron probe microanalysis, thermogravimetric analysis and differential scanning calorimetry coupled with in situ mass spectrometry, and high-temperature oxide melt solution calorimetry. This work confirms the energetic metastability of coffinite, USiO 4, and U-rich intermediate silicate phases with respect to a mixture of binary oxides. Furthermore, variations in unit cell parameters and negative excess volumesmore » of mixing, coupled with strongly exothermic enthalpies of mixing in the solid solution, suggest short-range cation ordering that can stabilize intermediate compositions, especially near x = 0.5.« less

Evolution of the magnetic and structural properties of Fe 1 - x Co x V 2 O 4

DOE PAGES

Sinclair, R.; Ma, Jie; Cao, H. B.; ...

2015-10-12

The magnetic and structural properties of single-crystal Fe 1-xCo xV 2O 4 samples have been investigated by performing specific heat, susceptibility, neutron diffraction, and x-ray diffraction measurements. As the orbital-active Fe 2+ ions with larger ionic size are gradually substituted by the orbital-inactive Co 2+ ions with smaller ionic size, the system approaches the itinerant electron limit with decreasing V-V distance. Then, various factors such as the Jahn-Teller distortion and the spin-orbital coupling of the Fe 2+ ions on the A sites and the orbital ordering and electronic itinerancy of the V 3+ ions on the B sites compete withmore » each other to produce a complex magnetic and structural phase diagram. Finally, this phase diagram is compared to those of Fe 1-xMn xV 2O 4 and Mn 1-xCo xV 2O 4 to emphasize several distinct features.« less

TiO x -Based Thermoelectric Modules: Manufacturing, Properties, and Operational Behavior

NASA Astrophysics Data System (ADS)

Martin, Hans-Peter; Pönicke, Andreas; Kluge, Martin; Sichert, Ina; Rost, Axel; Conze, Susan; Wätzig, Katja; Schilm, Jochen; Michaelis, Alexander

2016-03-01

Substoichiometric titanium oxides are attractive thermoelectric materials for high-temperature modules. Their advantages are availability, economy, and safety. This paper gives results of thermoelectric data on scale-up titanium suboxides, manufacturing technologies of TiO x modules, glass coating as an option for oxidation protection, and test results of TiO x modules. The thermoelectric efficiency of TiO x is low compared with established thermoelectric materials. However, TiO x is very attractive for economic reasons, and there are still expectations for efficiency rise by modification of the material's microstructure. TiO x can be produced in large quantities of several tens of kilograms. A manufacturing process for TiO x -based unileg n-type modules has been established, including all technological steps. The design of the TiO x -based modules was optimized for the thermoelectric conversion process and thermal robustness. A test device was used for experimental analysis with maximum temperature of 600°C at the hot side and 100°C at the cold side. This initial test revealed similar power output and internal resistance of all fabricated modules. Furthermore, thermal cycles with increasing and decreasing temperatures at the hot side were realized to characterize the reliability and stability of the modules. Additionally, modules were tested in a hot gas test rig to simulate the thermal stresses during power generation in the exhaust line of a passenger car.

ZnO-Assisted Growth of CH3NH3PbI3- xCl x Film and Efficient Planar Perovskite Solar Cells with a TiO2/ZnO/C60 Electron Transport Trilayer.

PubMed

Xu, Jia; Fang, Mingde; Chen, Jing; Zhang, Bing; Yao, Jianxi; Dai, Songyuan

2018-06-06

Appropriate electron transport layers (ETL) are essential in perovskite solar cells (PSCs) with high power conversion efficiency (PCE). Herein, a TiO 2 /ZnO/C 60 trilayer fabricated on a transparent fluorine-doped tin oxide (FTO) glass substrate is used as a compound ETL in planar PSCs. The trilayer shows positive effects on both perovskite synthesis and device performance. The ZnO layer assists growth of CH 3 NH 3 PbI 3- x Cl x ( x ≈ 0) annealed at a lower temperature and with a shorter time, which is due to a more rapid and easier decomposition of the intermediate CH 3 NH 3 PbCl 3 phase in the growth of CH 3 NH 3 PbI 3- x Cl x . All three materials in the trilayer are important for obtaining PSCs with a high PCE. ZnO is critical for enhancing the open circuit voltage by ensuring proper energy alignment with the TiO 2 and C 60 layers. C 60 enhances carrier extraction from the CH 3 NH 3 PbI 3- x Cl x layer. TiO 2 eliminates charge recombination at the FTO surface and ensures efficient electron collection. The best-performing PSC based on the TiO 2 /ZnO/C 60 electron transport trilayer features a PCE of 18.63% with a fill factor of 79.12%. These findings help develop an understanding of the effects of ZnO-containing ETLs on perovskite film synthesis and show promise for the future development of high-performance PSCs with compound ETLs.

Oxygen mobility in CeO{sub 2} and Ce{sub x}Zr({sub 1-x})O{sub 2} compounds: Study by CO transient oxidation and {sup 18}O/{sup 16}O isotopic exchange

DOE Office of Scientific and Technical Information (OSTI.GOV)

Madier, Y.; Descorme, C.; Govic, A.M. Le

Cerium-zirconium mixed oxides (Ce{sub x}Zr{sub 1{minus}x}O{sub 2}), precalcined at 900 C in dry air, were supplied by Rhodia Terres Rares as monophasic solid solutions. Introduction of some zirconium atoms in the ceria lattice by isomorphous substitution clearly influences the final properties of these materials as long as the cubic structure of ceria is maintained. Modifications in oxygen storage capacity (OSC measurements), redox properties (CO TPR), and oxygen exchange processes (TPIE) were studied. Ce{sub 0.63}Zr{sub 0.37}O{sub 2} was shown to have the most promising properties with the largest OSC at 400 C and the highest reactivity in O{sub 2} exchange. Allmore » mixed oxides are able to exchange very large amounts of oxygen compared to ceria, implying the participation of bulk oxygen. Furthermore, on Ce{sub x}Zr{sub (1{minus}x)}O{sub 2} samples, oxygen is predominantly exchanged via a multiple heteroexchange mechanism involving surface dioxygen species as superoxides or peroxides.« less

Hard X-ray photoelectron spectroscopy of Li{sub x}Ni{sub 1−x}O epitaxial thin films with a high lithium content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumara, L. S. R., E-mail: KUMARA.Rosantha@nims.go.jp; Yang, Anli; Sakata, Osami, E-mail: SAKATA.Osami@nims.go.jp

2014-07-28

The core-level and valence-band electronic structures of Li{sub x}Ni{sub 1−x}O epitaxial thin films with x = 0, 0.27, and 0.48 were studied by hard X-ray photoelectron spectroscopy. A double peak structure, consisting of a main peak and a shoulder peak, and a satellite structure were observed in the Ni 2p{sub 3/2} core-level spectra. The intensity ratio of the shoulder to main peak in this double peak structure increased with increasing lithium content in Li{sub x}Ni{sub 1−x}O. This lithium doping dependence of the Ni 2p{sub 3/2} core-level spectra was investigated using an extended cluster model, which included the Zhang–Rice (ZR) doubletmore » bound states arising from a competition between O 2p – Ni 3d hybridization and the Ni on-site Coulomb interaction. The results indicated that the change in the intensity ratio in the main peak is because of a reduction in the ZR doublet bound states from lithium substitutions. This strongly suggests that holes compensating Li doping in Li{sub x}Ni{sub 1−x}O are of primarily ZR character.« less

Structures, thermal expansion properties and phase transitions of Er{sub x}Fe{sub 2-x}(MoO{sub 4}){sub 3} (0.0 {le} x {le} 2.0).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Y. Z.; Wu, M. M.; Peng, J.

2007-05-03

Structures, thermal expansion properties and phase transitions of Er{sub x}Fe{sub 2-x}(MoO{sub 4}){sub 3} (0.0 {le} x {le} 2.0) have been investigated by X-ray diffraction and differential thermal analysis. The partial substitution of Er{sup 3+} for Fe{sup 3+} induces pronounced decreases in the phase transition temperature from monoclinic to orthorhombic structure. Rietveld analysis of the XRD data shows that both the monoclinic and orthorhombic Fe{sub 2}(MoO{sub 4}){sub 3}, as well as the orthorhombic Er{sub x}Fe{sub 2-x}(MoO{sub 4}){sub 3} (x {le} 0.8) have positive thermal expansion coefficients. However, the linear thermal expansion coefficients of Er{sub x}Fe{sub 2-x}(MoO{sub 4}){sub 3} (x = 0.6-2.0)more » decrease with increasing content of Er{sup 3+} and for x {ge} 1.0, compounds Er{sub x}Fe{sub 2-x}(MoO{sub 4}){sub 3} show negative thermal expansion properties. Attempts for making zero thermal expansion coefficient materials result in that very low negative thermal expansion coefficient of -0.60 x 10{sup -6} C in Er{sub 1.0}Fe{sub 1.0}(MoO{sub 4}){sub 3} is observed in the temperature range of 180-400 C, and zero thermal expansion is observed in Er{sub 0.8}Fe{sub 1.2}(MoO{sub 4}){sub 3} in the temperature range of 350-450 C. In addition, anisotropic thermal expansions are found for all the orthorhombic Er{sub x}Fe{sub 2-x}(MoO{sub 4}){sub 3} compounds, with negative thermal expansion coefficients along the a axes.« less

Fabrication of Mg-X-O (X = Fe, Co, Ni, Cr, Mn, Ti, V, and Zn) barriers for magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Yakushiji, K.; Kitagawa, E.; Ochiai, T.; Kubota, H.; Shimomura, N.; Ito, J.; Yoda, H.; Yuasa, S.

2018-05-01

We fabricated magnetic tunnel junctions with a 3d-transition material(X)-doped MgO (Mg-X-O) barrier, and evaluated the effect of the doping on magnetoresistance (MR) and microstructure. Among the variations of X (X = Fe, Co, Ni, Cr, Mn, Ti, V, and Zn), X = Fe and Mn showed a high MR ratio of more than 100%, even at a low resistance-area product of 3 Ωμm2. The microstructure analysis revealed that (001) textured orientation formed for X = Fe and Mn despite substantial doping (about 10 at%). The elemental mappings indicated that Fe atoms in the Mg-Fe-O barrier were segregated at the interfaces, while Mn atoms were evenly involved in the Mg-Mn-O barrier. This suggests that MgO has high adaptability for Fe and Mn dopants in terms of high MR ratio.

Optical properties of (AlxGa1-x)2O3 on sapphire

NASA Astrophysics Data System (ADS)

Hu, Zhuangzhuang; Feng, Qian; Zhang, Jincheng; Li, Fuguo; Li, Xiang; Feng, Zhaoqing; Zhang, Chunfu; Hao, Yue

2018-02-01

The (AlxGa1-x)2O3 and Ga2O3 films are epitaxially grown on sapphire by pulsed laser deposition (PLD). From X-ray photoelectron spectroscopy (XPS) and X-ray diffraction measurements, the (AlxGa1-x)2O3 films with Al compositions of 0.39, 0.49 and up to 0.53 are all single crystal and there is an out-of-plane tensile strain in (AlxGa1-x)2O3 films within the range from 0.164% to 0.345%. The optical properties are investigated by Spectral Ellipsometry (SE) together with the optical transmission method. The spectral dependence of the refractive index (n) by SE is in accordance with the reported experiment results. The thicknesses of the Ga2O3 and (AlxGa1-x)2O3 films obtained by SE fitting are 201, 116.8, 40 and 84.61 nm, respectively, which is consistent with the field emission scanning electron microscopy (FESEM) measurement results. In addition, with the Al composition increasing, the bandgaps of the (AlxGa1-x)2O3 films determined from the SE are both increase from 4.95 to 5.49, 5.7 and 5.75 eV, almost identical to the values determined by the transmittance spectra, which is larger than some extent compared to reference [13] for the compressive strain in the (AlxGa1-x)2O3 films.

Phase diagram and polarization of stable phases of (Ga1- x In x )2O3

NASA Astrophysics Data System (ADS)

Maccioni, Maria Barbara; Fiorentini, Vincenzo

2016-04-01

The full phase diagram of (Ga1- x In x )2O3 is obtained theoretically. The phases competing for the ground state are monoclinic β (low x), hexagonal (x ˜ 0.5), and bixbyite (large x). Three disconnected mixing regions interlace with two distinct phase-separation regions, and at x ˜ 0.5, the coexistence of hexagonal and β alloys with phase-separated binary components is expected. We also explore the permanent polarization of the phases, but none of them are polar. On the other hand, we find that ɛ-Ga2O3, which was stabilized in recent experiments, is pyroelectric with a large polarization and piezoelectric coupling, and could be used to produce high-density electron gases at interfaces.

Zn(1-x)Cu(x)O (0.02 ≤ x ≤ 0.1) Nanomaterials Prepared by Ball Milling, Citrate Sol Gel, and Molten Salt Flux Methods.

PubMed

Balamurugan, S; Melba, K

2015-06-01

The Cu doped ZnO, (Zn(1-x)Cu(x))O (x = 0.02, 0.04, 0.06, 0.08, and 0.1) nanomaterials were prepared by ball milling technique (BMT), citrate sol gel (CSG), and molten salt flux (MSF) methods. The various as-prepared (Zn(1-x)Cu(x))O materials were analyzed by powder X-ray diffraction (pXRD), FT-IR, and SEM-EDX measurements in order to check the phase formation, purity, surface morphology and elements present in the annealed materials. Due to the preparation methods as well as doping of 'x' slight variations in cell parameters are seen. The average crystalline size of CSG method shows smaller size (25-35 nm) than BMT and MSF approaches. The materials obtained by MSF technique reveal the average crystalline size in the range of 32-72 nm whereas the BMT materials exhibit 36-50 nm for the composition, 0.02 ≤ x ≤ 0.1. The presence of functional groups and the chemical bonding in (Zn(1-x)Cu(x))O system is confirmed through FT-IR measurements. It is evident from the FT-IR data that bands seen at 400-500 cm(-1) are characteristics of M-O (M = metal ion) bonding in the studied materials. The micro images observed by SEM exhibiting polycrystalline character as compared with the crystallite size obtained from XRD. Among the three approaches employed in the present investigations, in terms of average particle size the CSG method may be concluded as an efficient method for the preparation of Zn(1-x)Cu(x)O nanomaterials.

Understanding the optical properties of ZnO1-xSx and ZnO1-xSex alloys

NASA Astrophysics Data System (ADS)

Baldissera, Gustavo; Persson, Clas

2016-01-01

ZnO1-xYx with chalcogen element Y exhibits intriguing optoelectronic properties as the alloying strongly impacts the band-gap energy Eg(x). In this work, we analyze and compare the electronic structures and the dielectric responses of Zn(O,S) and Zn(O,Se) alloys by means of the density functional theory and the partially self-consistent GW approach. We model the crystalline stability from the total energies, and the results indicate that Zn(O,S) is more stable as alloy than Zn(O,Se). We demonstrate also that ion relaxation strongly affects total energies, and that the band-gap bowing depends primarily on local relaxation of the bonds. Moreover, we show that the composition dependent band-gap needs to be analyzed by the band anti-crossing model for small alloying concentration, while the alloying band-bowing model is accurate for strong alloying. We find that the Se-based alloys have a stronger change in the band-gap energy (for instance, ΔEg(0.50) = Eg(ZnO) - Eg(x = 0.50) ≈ 2.2 eV) compared with that of the S-based alloy (ΔEg(0.50) = 1.2 eV), mainly due to a stronger relaxation of the Zn-anion bonds that affects the electronic structure near the band edges. The optical properties of the alloys are discussed in terms of the complex dielectric function ɛ(ω) = ɛ1(ω) + iɛ2(ω) and the absorption coefficient α(ω). While the large band-gap bowing directly impacts the low-energy absorption spectra, the high-frequency dielectric constant ɛ∞ is correlated to the intensity of the dielectric response at energies above 4 eV. Therefore, the dielectric constant is only weakly affected by the non-linear band-gap variation. Despite strong structural relaxation, the high absorption coefficients of the alloys demonstrate that the alloys have well-behaved optoelectronic properties.

High-rate deposition of LiNb 1- xTa xO 3 films by thermal plasma spray CVD

NASA Astrophysics Data System (ADS)

Majima, T.; Yamamoto, H.; Kulinich, S. A.; Terashima, K.

2000-12-01

LiNb 1- xTa xO 3 films were prepared by a thermal plasma spray CVD method using liquid source materials. Preferentially (0 0 1)-oriented LiNb 1- xTa xO 3 films with satisfactory in-plane and out-of-plane alignment were fabricated on sapphire (0 0 1) substrates. The full-width at half-maximum (FWHM) of the (0 0 6) rocking curve could achieve 0.12°, which was comparable with those of LiNbO 3 and LiTaO 3 films prepared by other conventional vapor-phase deposition methods. The deposition rate was up to 0.07 μm/min, which was 5-40 times faster than those for most other conventional vapor-phase deposition methods. From inductively coupled plasma atomic emission spectroscopy analysis, x values of these films were estimated to be 0.36-0.49.

Electron holography on HfO2/HfO2-x bilayer structures with multilevel resistive switching properties

NASA Astrophysics Data System (ADS)

Niu, G.; Schubert, M. A.; Sharath, S. U.; Zaumseil, P.; Vogel, S.; Wenger, C.; Hildebrandt, E.; Bhupathi, S.; Perez, E.; Alff, L.; Lehmann, M.; Schroeder, T.; Niermann, T.

2017-05-01

Unveiling the physical nature of the oxygen-deficient conductive filaments (CFs) that are responsible for the resistive switching of the HfO2-based resistive random access memory (RRAM) devices represents a challenging task due to the oxygen vacancy related defect nature and nanometer size of the CFs. As a first important step to this goal, we demonstrate in this work direct visualization and a study of physico-chemical properties of oxygen-deficient amorphous HfO2-x by carrying out transmission electron microscopy electron holography as well as energy dispersive x-ray spectroscopy on HfO2/HfO2-x bilayer heterostructures, which are realized by reactive molecular beam epitaxy. Furthermore, compared to single layer devices, Pt/HfO2/HfO2-x /TiN bilayer devices show enhanced resistive switching characteristics with multilevel behavior, indicating their potential as electronic synapses in future neuromorphic computing applications.

Importance of Low Dimensional CeO x Nanostructures in Pt/CeO x –TiO 2 Catalysts for the Water–Gas Shift Reaction

DOE PAGES

Luo, Si; Barrio, Laura; Nguyen-Phan, Thuy-Duong; ...

2017-03-15

CO 2 and H 2 production from the water–gas shift (WGS) reaction was studied over Pt/CeO x–TiO 2 catalysts with incremental loadings of CeO x, which adopts variations in the local morphology. The lowest loading of CeO x (1 wt % to 0.5 at. %) that is configured in its smallest dimensions exhibited the best WGS activity over larger dimensional structures. We attribute this to several factors including the ultrafine dispersed one-dimensional nanocluster geometry, a large concentration of Ce 3+ and enhanced reducibility of the low loadings. We utilized several in situ experiments to monitor the active state of themore » catalyst during the WGS reaction. X-ray diffraction (XRD) results showed lattice expansion that indicated reduced ceria was prevalent during the WGS reaction. On the surface, Ce 3+ related hydroxyl groups were identified by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The enhanced reducibility of the catalyst with the introduction of ceria was further revealed by H 2-temperature programed reduction (H 2-TPR) and good thermal stability was confirmed by in situ environmental transmission electron microscopy (ETEM). Finally, we also investigated the formation of the low dimensional structures during catalyst preparation, through a two-stage crystal growth of ceria crystallite on TiO 2 nanoparticle: fine crystallites ~1D formed at ~250 °C, followed by crystal growth into 2D chain and 3D particle from 250–400 °C.« less

Magnetic Structure and Magnetotransport Properties of La0.7Sr0.3Mn1 - x Ni x O3

NASA Astrophysics Data System (ADS)

Troyanchuk, I. O.; Bushinsky, M. V.; Tereshko, N. V.; Sikolenko, V.; Schorr, S.

2018-04-01

La0.7Sr0.3Mn1 - x Ni x O3 (0.12 ≤ x ≤ 0.35) compositions have been studied using neutron diffraction, magnetometry, and measurements of magnetotransport properties. At temperatures of 5-300 K, these compounds were found to have a rhombohedral crystal structure. The substitution of nickel for manganese has been shown to result in a decrease in the Curie temperature from 278 K ( x = 0.12) to 60 K ( x = 0.3); in this case, the spontaneous magnetization of the compositions decreases to zero ( x = 0.33). The magnetoresistive effect for the semimetals with 0.12 ≤ x < 0.18 increases near the Curie temperature, whereas the magnetoresistance of semiconducting compositions with x ≥ 0.2 progressively decreases as the temperature increases. For compositions with x ≥ 0.25, an antiferromagnetic G-type component has been found by neutron diffraction, the Neel temperature of which reaches 260 K (at x = 0.35). The study of the La1- y Sr y Mn0.65Ni0.35O3 ( y ≤ 0.3) system showed that the content of ferromagnetic component decreases with increasing Sr content. It has been inferred that the antiferromagnetism of the compositions with x > 0.25 is due to the strong negative exchange interactions Ni2+-O-Ni2+ and Mn4+-O-Mn4+ and the absence of ionic order. The obtained data have been used to construct the magnetic phase diagram of the La0.7Sr0.3Mn1- x Ni x O3 (0.12 ≤ x ≤ 0.35) system.

Structural, Dielectric, and Electrical Properties of Bi1- x Pb x Fe1- x (Zr0.5Ti0.5) x O3

NASA Astrophysics Data System (ADS)

Panda, Niranjan; Pattanayak, Samita; Choudhary, R. N. P.

2015-12-01

Polycrystalline samples of Bi1- x Pb x Fe1- x (Zr0.5Ti0.5) x O3 (BPFZTO) with x = 0.0, 0.2, 0.3, and 0.4 were prepared by high-temperature solid-state reaction. Preliminary structural analysis of calcined powders of the materials by use of x-ray powder diffraction confirmed formation of single-phase systems with the tetragonal structure. Room-temperature scanning electron micrographs of the samples revealed uniform distribution of grains of low porosity and different dimensions on the surface of the samples. The frequency-temperature dependence of dielectric and electric properties was studied by use of dielectric and complex impedance spectroscopy over a wide range of frequency (1 kHz to 1 MHz) at different temperatures (25-500°C). The dielectric constant of BiFeO3 (BFO) was enhanced by substitution with Pb(Zr0.5Ti0.5)O3 (PZT) whereas the dielectric loss of the BPFZTO compounds decreased with increasing PZT content. A significant contribution of both grains and grain boundaries to the electrical response of the materials was observed. The frequency-dependence of the ac conductivity of BPFZTO followed Jonscher's power law. Negative temperature coefficient of resistance behavior was observed for all the BPFZTO samples. Conductivity by thermally excited charge carriers and oxygen vacancies in the materials was believed to be of the Arrhenius-type.

On the Samarium Substitution Effects in Y3-x Sm x Al5O12 (x = 0.1-3.0)

NASA Astrophysics Data System (ADS)

Skaudzius, Ramunas; Sakirzanovas, Simas; Kareiva, Aivaras

2018-04-01

Yttrium aluminium garnet substituted by samarium Y3-x Sm x Al5O12, (YSmAG, x = 0.1, 0.15, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5 and 3.0) was prepared by an aqueous sol-gel processing using etane-1,2-diol as complexing agent. The end products obtained at 1000°C in air were characterized by x-ray diffraction analysis, infrared spectroscopy (FT-IR) and scanning electron microscopy. It was demonstrated, however, that the total substitution of yttrium by samarium does not proceed in the YSmAG. The single cubic garnet phase was formed only at a low concentration of samarium (x = 0.1, 0.15, 0.25, 0.5, 0.75, 1.0). With further substitutional levels, if the amount of samarium was x = 1.5, 2.0, 2.5 and 3, respectively, the formation a of minor amount of side perovskite samarium aluminate SmAlO3 (SmAP) phase was observed. Surprisingly, when yttrium was totally replaced by the samarium (x = 3.0) the main synthesis product was SmAP. The possible formation of Sm3Al5O12 (SmAG) garnet was also investigated for the first time by variation of the temperature in the range of 780-835°C.

Magnetoresistance Versus Oxygen Deficiency in Epi-stabilized SrRu1 - x Fe x O3 - δ Thin Films

NASA Astrophysics Data System (ADS)

Dash, Umasankar; Acharya, Susant Kumar; Lee, Bo Wha; Jung, Chang Uk

2017-03-01

Oxygen vacancies have a profound effect on the magnetic, electronic, and transport properties of transition metal oxide materials. Here, we studied the influence of oxygen vacancies on the magnetoresistance (MR) properties of SrRu1 - x Fe x O3 - δ epitaxial thin films ( x = 0.10, 0.20, and 0.30). For this purpose, we synthesized highly strained epitaxial SrRu1 - x Fe x O3 - δ thin films with atomically flat surfaces containing different amounts of oxygen vacancies using pulsed laser deposition. Without an applied magnetic field, the films with x = 0.10 and 0.20 showed a metal-insulator transition, while the x = 0.30 thin film showed insulating behavior over the entire temperature range of 2-300 K. Both Fe doping and the concentration of oxygen vacancies had large effects on the negative MR contributions. For the low Fe doping case of x = 0.10, in which both films exhibited metallic behavior, MR was more prominent in the film with fewer oxygen vacancies or equivalently a more metallic film. For semiconducting films, higher MR was observed for more semiconducting films having more oxygen vacancies. A relatively large negative MR ( 36.4%) was observed for the x = 0.30 thin film with a high concentration of oxygen vacancies ( δ = 0.12). The obtained results were compared with MR studies for a polycrystal of (Sr1 - x La x )(Ru1 - x Fe x )O3. These results highlight the crucial role of oxygen stoichiometry in determining the magneto-transport properties in SrRu1 - x Fe x O3 - δ thin films.

Influence of Ga-concentration on the electrical and magnetic properties of magnetoelectric CoGa xFe 2–xO 4/BaTiO 3 composite

DOE PAGES

Ni, Yan; Zhang, Zhen; Nlebedim, Cajetan I.; ...

2015-03-20

Multiferroic materials exhibit magnetoelectric (ME) coupling and promise new device applications including magnetic sensors, generators, and filters. An effective method for developing ME materials with enhanced ME effect is achieved by the coupling through the interfacial strain between piezoelectric and magnetostrictive materials. In this study, the electrical and magnetic properties of Ga doped magnetoelectric CoGa xFe 2–xO 4/BaTiO 3 composite are studied systematically. It is found that Ga doping improves the sensitivity of magnetoelastic response and stabilizes the magnetic phase of the composites. More importantly, Ga doping reduces the electrical conductivity of composite, as well as the dielectric loss. Anmore » enhancement of the electrostrain with doping Ga is also observed. Quantitative estimation indicates that magnetoelectric coupling is enhanced for Ga-doped CoGa xFe 2–xO 4/BaTiO 3 composites. As a result, the present work is beneficial to the practical application of composite CoFe 2O 4/BaTiO 3-based multiferroic materials.« less

Enhancement of magnetic ordering temperature in iron substituted ytterbium manganate (YbMn{sub 1-x}Fe{sub x}O{sub 3})

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samal, S.L.; Magdaleno, T.; Ramanujachary, K.V.

Oxides of the type YbMn{sub 1-x}Fe{sub x}O{sub 3}; x<=0.3 showing multiferroic behavior have been synthesized by the solid state route. These oxides crystallize in the hexagonal structure known for the parent YbMnO{sub 3} with the c/a ratio increasing with Fe substitution. The distortion of the MnO{sub 5} polyhedra (tbp) decreases and the Mn-O-Mn bonds in the a-b plane become shorter with Fe-substitution. Magnetic ordering is observed from the low temperature neutron diffraction study. The compounds were found to be antiferromagnetic and the ordering temperature T{sub N} increased from 82 K for pure YbMnO{sub 3} to 95 K for YbMn{sub 0.7}Fe{submore » 0.3}O{sub 3}. Variable temperature dielectric measurements (15-110 K) show an anomaly in the dielectric constant at temperatures close to the antiferromagnetic ordering temperature for all the compositions, showing a unique correlation between the magnetic and electric field. The increase in the ordering temperature in YbMn{sub 1-x}Fe{sub x}O{sub 3} is explained on the basis of increase in covalence of Mn/Fe-O-Mn/Fe bonds (shorter) with iron substitution. - Graphical abstract: Hexagonal manganites of the type YbMn{sub 1-x}Fe{sub x}O{sub 3}; x<=0.3 have been synthesized by the solid state route. The distortion of the MnO{sub 5} polyhedra (tbp) decreases and the Mn-O-Mn bonds in the a-b plane become shorter with Fe-substitution. The compounds were found to be antiferromagnetic and the ordering temperature T{sub N} increased from 82 K for pure YbMnO{sub 3} to 95 K for YbMn{sub 0.7}Fe{sub 0.3}O{sub 3}. The increase in the ordering temperature in YbMn{sub 1-x}Fe{sub x}O{sub 3} is explained on the basis of increase in covalence of Mn/Fe-O-Mn/Fe bonds with iron substitution. Low temperature dielectric measurements show a unique correlation between the magnetic and electric fields for all compositions.« less

Epitaxial structure and transport in LaTiO3+x films on (001) SrTiO3

NASA Astrophysics Data System (ADS)

Kim, K. H.; Norton, D. P.; Budai, J. D.; Chisholm, M. F.; Sales, B. C.; Christen, D. K.; Cantoni, C.

2003-12-01

The structure and transport properties of LaTiO3+x epitaxial thin films grown on (001) SrTiO3 by pulsed-laser deposition is examined. Four-circle X-ray diffraction indicates that the films possess the defect perovskite LaTiO3 structure when deposited in vacuum, with the higher X compounds forming at moderate oxygen pressures. The crystal structure of the LaTiO3 films is tetragonal in the epitaxial films, in contrast to the orthorhombic structure observed in bulk materials. A domain structure is observed in the films, consisting of LaTiO3 oriented either with the [110] or [001] directions perpendicular to the substrate surface. Z-contrast scanning transmission electron microscopy reveals that this domain structure is not present in the first few unit cells of the film, but emerges approximately 2-3 nm from the SrTiO3/LaTiO3 interface. Upon increasing the oxygen pressure during growth, a shift in the lattice d-spacing parallel to the substrate surface is observed, and is consistent with the growth of the La2Ti2O7 phase. However, van der Pauw measurements show that the films with the larger d-spacing remain conductive, albeit with a resistivity that is significantly higher than that for the perovskite LaTiO3 films. The transport behavior suggests that the films grown at higher oxygen pressures are LaTiO3+x with 0.4 < x < 0.5. (

Theoretical band structure of the superconducting antiperovskite oxide Sr3-xSnO

NASA Astrophysics Data System (ADS)

Ikeda, Atsutoshi; Fukumoto, Toshiyuki; Oudah, Mohamed; Hausmann, Jan Niklas; Yonezawa, Shingo; Kobayashi, Shingo; Sato, Masatoshi; Tassel, Cédric; Takeiri, Fumitaka; Takatsu, Hiroshi; Kageyama, Hiroshi; Maeno, Yoshiteru

2018-05-01

In order to investigate the position of the strontium deficiency in superconductive Sr3-xSnO, we synthesized and measured X-ray-diffraction patterns of Sr3-xSnO (x ∼ 0.5). Because no clear peaks originating from superstructures were observed, strontium deficiency is most likely to be randomly distributed. We also performed first-principles band-structure calculations on Sr3-xSnO (x = 0, 0.5) using two methods: full-potential linearized-augmented plane-wave plus local orbitals method and the Korringa-Kohn-Rostoker Green function method combined with the coherent potential approximation. We revealed that the Fermi energy of Sr3-xSnO in case of x ∼ 0.5 is about 0.8 eV below the original Fermi energy of the stoichiometric Sr3SnO, where the mixing of the valence p and conduction d orbitals are considered to be small.

Stabilized antiferroelectricity in xBiScO3-(1-x)NaNbO3 lead-free ceramics with established double hysteresis loops

NASA Astrophysics Data System (ADS)

Gao, Lisheng; Guo, Hanzheng; Zhang, Shujun; Randall, Clive A.

2018-02-01

We previously reported various solid solution systems that demonstrated the stabilized antiferroelectric (P) phases in NaNbO3 through lowering the tolerance factor. However, all those reported modifications were achieved by adding A2+B4+O3 type solid solutions. A lead-free antiferroelectric (AFE) solid solution xBiScO3-(1-x)NaNbO3 was rationalized by adopting the tolerance factor design rule. Specifically, adding BiScO3 was found to effectively stabilize the AFE phase without changing the crystal symmetry of NaNbO3. Microstructure and electron zone axis diffraction patterns from transmission electron microscopy revealed the stabilized AFE (P) phase in this solid solution. Besides, the electric-field-induced polarization with a double-hysteresis loop was observed. The present results pointed out that the strategy could also be applied while adding A3+B3+O3 type solid solutions. In addition, it expanded the compositional design that can be applied to antiferroelectric materials.

Synthesis and morphology of Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals with tungsten bronze structure in RE{sub 2}O{sub 3}-BaO-Nb{sub 2}O{sub 5}-B{sub 2}O{sub 3} glasses (RE: Sm, Eu, Gd, Dy, Er)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ida, H.; Shinozaki, K.; Honma, T.

2012-12-15

Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals with a tetragonal tungsten bronze (TTB) structure are synthesized using a conventional glass crystallization technique in 2.3RE{sub 2}O{sub 3}-27.4BaO-34.3Nb{sub 2}O{sub 5}-36B{sub 2}O{sub 3} (mol%) (RE=Sm, Eu, Gd, Dy, and Er) glasses. One sharp crystallization peak is observed at {approx}670 Degree-Sign C in both powdered and bulk glasses, and the formation of Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals with unit cell parameters of a{approx}1.24 nm and c{approx}0.39 nm was confirmed. It is found from high resolution transmission electron microscope observations that the morphology of Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals is ellipsoidal. Their average particlemore » size is in the range of 15-60 nm and decreases with decreasing ionic radius of RE{sup 3+} being present in the precursor glasses. The optical transparent crystallized glass (bulk) shows the total photoluminescence (PL) quantum yield of 53% in the visible region of Eu{sup 3+} ions, suggesting a high potential of Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals as PL materials. - Graphical abstract: This figure shows a TEM photograph for the heat-treated (667 Degree-Sign C, 3 h) sample of 2.3Dy{sub 2}O{sub 3}-27.4BaO-34.3Nb{sub 2}O{sub 5}-36B{sub 2}O{sub 3}. An ellipsoidal-shaped Ba{sub 1-x}Dy{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystal with diameters of 17 and 28 nm is observed. The ellipsoidal morphology is a common feature in Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals synthesized by the crystallization of 2.3RE{sub 2}O{sub 3}-27.4BaO-34.3Nb{sub 2}O{sub 5}-36B{sub 2}O{sub 3} glasses. Highlights: Black-Right-Pointing-Pointer Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals with a tetragonal tungsten bronze structure are synthesized. Black-Right-Pointing-Pointer A glass crystallization technique was applied. Black-Right-Pointing-Pointer The morphology of Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals

Direct spectroscopic evidence for isolated silanols in SiO x/Al 2O 3 and their formation mechanism

DOE PAGES

Mouat, Aidan R.; Kobayashi, Takeshi; Pruski, Marek; ...

2017-02-27

Here, the preparation and unambiguous characterization of isolated Brønsted-acidic silanol species on silica–alumina catalysts presents a key challenge in the rational design of solid acid catalysts. In this report, atomic layer deposition (ALD) and liquid-phase preparation (chemical liquid deposition, CLD) are used to install the SiO x sites on Al 2O 3 catalysts using the same Si source (tetraethylorthosilicate, TEOS). The ALD-derived and CLD-derived SiO x sites are probed with dynamic nuclear polarization (DNP)-enhanced 29Si– 29Si double-quantum/single-quantum (DQ/SQ) correlation NMR spectroscopy. The investigation reveals conclusively that the SiO x/Al 2O 3 material prepared by ALD and CLD, followed by calcinationmore » under an O 2 stream, contains fully spatially isolated Si species, in contrast with those resulting from the calcination under static air, which is widely accepted as a postgrafting treatment for CLD. Insight into the formation mechanism of these sites is obtained via in situ monitoring of the TEOS + γ-Al 2O 3 reaction in an environmental diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) cell. Upon calcination, the DRIFTS spectra of SiO x/Al 2O 3 reveal a signature unambiguously assignable to isolated Brønsted-acidic silanol species. Surprisingly, the results of this study indicate that the method of preparing SiO x/Al 2O 3 catalysts is less important to the final structure of the silanol sites than the post-treatment conditions. This finding should greatly simplify the methods for synthesizing site-isolated, Brønsted-acidic SiO x/Al 2O 3 catalysts.« less

Band-gap tailoring and visible-light-driven photocatalytic performance of porous (GaN)1-x(ZnO)x solid solution.

PubMed

Wu, Aimin; Li, Jing; Liu, Baodan; Yang, Wenjin; Jiang, Yanan; Liu, Lusheng; Zhang, Xinglai; Xiong, Changmin; Jiang, Xin

2017-02-21

(GaN) 1-x (ZnO) x solid solution has attracted extensive attention due to its feasible band-gap tunability and excellent photocatalytic performance in overall water splitting. However, its potential application in the photodegradation of organic pollutants and environmental processing has rarely been reported. In this study, we developed a rapid synthesis process to fabricate porous (GaN) 1-x (ZnO) x solid solution with a tunable band gap in the range of 2.38-2.76 eV for phenol photodegradation. Under visible-light irradiation, (GaN) 0.75 (ZnO) 0.25 solid solution achieved the highest photocatalytic performance compared to other (GaN) 1-x (ZnO) x solid solutions with x = 0.45, 0.65 and 0.85 due to its higher redox capability and lower lattice deformation. Slight Ag decoration with a content of 1 wt% on the surface of the (GaN) 0.75 (ZnO) 0.25 solid solution leads to a significant enhancement in phenol degradation, with a reaction rate eight times faster than that of pristine (GaN) 0.75 (ZnO) 0.25 . Interestingly, phenol in aqueous solution (10 mg L -1 ) can also be completely degraded within 60 min, even under the direct exposure of sunlight irradiation. The photocurrent response indicates that the enhanced photocatalytic activity of (GaN) 0.75 (ZnO) 0.25 /Ag is directly induced by the improved transfer efficiency of the photogenerated electrons at the interface. The excellent phenol degradation performance of (GaN) 1-x (ZnO) x /Ag further broadens their promising photocatalytic utilization in environmental processing, besides in overall water splitting for hydrogen production.

Formation, stability and crystal structure of mullite-type Al{sub 6−x}B{sub x}O{sub 9}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffmann, K., E-mail: Kristin.Hoffmann@uni-bremen.de; Institut für Anorganische Chemie und Kristallographie, FB02, Leobener Straße/NW2, Universität Bremen, D-28359 Bremen; Hooper, T.J.N.

2016-11-15

Mullite-type Al{sub 6−x}B{sub x}O{sub 9} compounds were studied by means of powder diffraction and spectroscopic methods. The backbones of this structure are chains of edge-connected AlO{sub 6} octahedra crosslinked by AlO- and BO-polyhedra. Rietveld refinements show that the a and b lattice parameters can be well resolved, thus representing an orthorhombic metric. A continuous decrease of the lattice parameters most pronounced in c-direction indicates a solid solution for Al{sub 6−x}B{sub x}O{sub 9} with 1.09≤x≤2. A preference of boron in 3-fold coordination is confirmed by {sup 11}B MAS NMR spectroscopy and Fourier calculations based on neutron diffraction data collected at 4more » K. Distance Least Squares modeling was performed to simulate a local geometry avoiding long B-O distances linking two octahedral chains by planar BO{sub 3} groups yielding split positions for the oxygen atoms and a strong distortion in the octahedral chains. The lattice thermal expansion was calculated using the Grüneisen first-order equation of state Debye-Einstein-Anharmonicity model. - Graphical abstract: Local distortion induced by boron linking the octahedral chains. - Highlights: • Decreasing lattice parameters indicate a solid solution for Al{sub 6−x}B{sub x}O{sub 9} (1.09≤x≤2). • B-atoms induce a local distortion of neighboring AlO{sub 6} octahedra. • A preference of boron in BO{sub 3} coordination is confirmed by {sup 11}B MAS NMR spectroscopy. • An optimized structural model for Al{sub 6−x}B{sub x}O{sub 9} is presented.« less

Ethanol Sensitivity of Cu1-xSnxO (x = 0.00, 0.03, and 0.05) Nanoflakes

NASA Astrophysics Data System (ADS)

Mariammal, R. N.; Ramachandran, K.

2011-07-01

Cu1-xSnxO (x = 0.00, 0.03, and 0.05) nanoflakes were synthesized by a simple wet chemical method and X-Ray diffraction (XRD) result confirms the monoclinic structure of CuO with no secondary phases due to Sn doping. The scanning electron microscopic images indicate the formation of nanoflakes. The fundamental Raman modes were observed at 273, 318, 610, and 1084 cm-1 for undoped CuO sample and theses modes were slightly shifted towards lower frequency side for Sn-doped samples, which indicates the inclusion of Sn in CuO. In addition, XRD and Raman studies infer the decrease of crystallinity in doped samples, which is reflected in the sensitivity towards ethanol. The ethanol sensitivity (resistivity measurement) increases with ethanol gas concentration and decreases with Sn-doping in CuO nanoflakes.

Combinatorial studies of (1-x)Na0.5Bi0.5TiO3-xBaTiO3 thin-film chips

NASA Astrophysics Data System (ADS)

Cheng, Hong-Wei; Zhang, Xue-Jin; Zhang, Shan-Tao; Feng, Yan; Chen, Yan-Feng; Liu, Zhi-Guo; Cheng, Guang-Xi

2004-09-01

Applying a combinatorial methodology, (1-x)Na0.5Bi0.5TiO3-xBaTiO3 (NBT-BT) thin-film chips were fabricated on (001)-LaAlO3 substrates by pulsed laser deposition with a few quaternary masks. A series of NBT-BT library with the composition of BT ranged from 0 to 44% was obtained with uniform composition and well crystallinity. The relation between the concentration of NBT-BT and their structural and dielectric properties were investigated by x-ray diffraction (XRD), evanescent microwave probe, atomic force microscopy, and Raman spectroscopy. An obvious morphotropic phase boundary (MPB) was established to be about 9% BT by XRD, Raman frequency shift, and dielectric anomaly, different from the well-known MPB of the materials. The result shows the high efficiency of combinatorial method in searching new relaxor ferroelectrics.

Phase transition, crystal water and low thermal expansion behavior of Al{sub 2−2x}(ZrMg){sub x}W{sub 3}O{sub 12}·n(H{sub 2}O)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Fang; Liu, Xiansheng; Song, Wenbo

2014-10-15

Al{sub 2−2x}(ZrMg){sub x}W{sub 3}O{sub 12} for 0≤x≤1.0 are synthesized to reduce the phase transition temperature of Al{sub 2}W{sub 3}O{sub 12}. It is found that the incorporation of (ZrMg){sup 6+} into the lattice of Al{sub 2}W{sub 3}O{sub 12} not only reduces its orthorhombic-to-monoclinic phase transition temperature but also elevates its softening temperature, broadening its applicable temperature range considerably. Al{sub 2−2x}(ZrMg){sub x}W{sub 3}O{sub 12} with x<0.5 exhibit low coefficients of thermal expansion (CTEs) and non-hygroscopicity, while those for x≥0.7 are obviously hygroscopic and the CETs decrease with increasing the content of (ZrMg){sup 6+} so that Al{sub 0.2}(ZrMg){sub 0.9}W{sub 3}O{sub 12} and ZrMgW{submore » 3}O{sub 12} exhibit negative thermal expansion. Temperature-dependent Raman spectroscopic study shows the hardening of W–O bonds above 373 K which is attributed to the release of crystal water. The effect of crystal water on the thermal expansion property is discussed based on the hydrogen bond between H in crystal water and electronegative O in Al(ZrMg)–O–W linkages. - Graphical abstract: (a and b) Temperature dependent Raman spectra of Al{sub 2−x}(ZrMg){sub x}W{sub 3}O{sub 12} (x=0.1, 0.2), (c and d) Building block of a unit cell of Al{sub 2−x}(ZrMg){sub x}W{sub 3}O{sub 12}·n(H{sub 2}O) and schematic showing the effect of crystal water on Al(Zr, Mg)–O–W linkages. - Highlights: • (ZrMg){sup 6+} reduces orthorhombic-to-monoclinic phase transition of Al{sub 2}W{sub 3}O{sub 12}. • The incorporation of (ZrMg){sup 6+} elevates the softening temperature of Al{sub 2}W{sub 3}O{sub 12}. • Al{sub 2−2x}(ZrMg){sub x}W{sub 3}O{sub 12} (x<0.5) exhibit low CTEs and non-hygroscopicity. • Al{sub 0.2}(ZrMg){sub 0.9}W{sub 3}O{sub 12}·0.8H{sub 2}O and ZrMgW{sub 3}O{sub 12}·2H{sub 2}O present NTE. • Hydrogen bond between H in H{sub 2}O and O in Al(ZrMg)–O–W affects thermal expansion.« less

Structural and magnetic phase transitions in EuTi 1-xNb xO 3

DOE PAGES

Li, Ling; Morris, James R.; Koehler, Michael R.; ...

2015-07-30

Here, we investigate the structural and magnetic phase transitions in EuTi 1-xNb xO 3 (0≤x≤0.3) with synchrotron powder x-ray diffraction, resonant ultrasound spectroscopy, and magnetization measurements. Upon Nb doping, the Pmmore » $$\\bar{3}$$m ↔ I4/mcm structural transition shifts to higher temperatures and the room temperature lattice parameter increases while the magnitude of the octahedral tilting decreases. In addition, Nb substitution for Ti destabilizes the antiferromagnetic ground state of the parent compound and long-range ferromagnetic order is observed in the samples with x≥0.1. Moreover, the structural transition in pure and doped compounds is marked by a dramatic step-like softening of the elastic moduli near T S, which resembles that of SrTiO 3 and can be adequately modeled using the Landau free energy model employing the same coupling between strain and octahedral tilting order parameter as previously used to model SrTiO 3.« less

Comparison of structural and magnetic properties of Zn{sub x}Mg{sub 1.5-x}Mn{sub 0.5}FeO{sub 4} and MgAl{sub x}Cr{sub x}Fe{sub 2-2x}O{sub 4} spinel oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thummer, K. P., E-mail: kpthummer@yahoo.co.in; Tanna, A. R., E-mail: ashish.tanna@rku.ac.in; Joshi, H. H.

2016-05-23

The spinel oxides Zn{sub x}Mg{sub 1.5-x}Mn{sub 0.5}FeO{sub 4} (x = 0.0 to 0.6) and MgAl{sub x}Cr{sub x}Fe{sub 2-2x}O{sub 4} (x = 0.0 to 0.6) abbreviated as ZMMFO and MACFO respectively, were synthesized by standard ceramic processing. The compositional purity of all the specimens was checked by EDAX technique. The X-ray diffractometry was employed to determine the lattice constants and distribution of cations in the interstitial voids. The initial decrease of cell edge parameter (a) for ZMMFO up to x = 0.2 and thereafter expected rise in the ‘a’ and the initial slower rate of reduction in the lattice constant formore » MACFO are explained as basic of cation occupancy. The magnetic ordering in both systems is explained by invoking statistical canting models. The compositional variation of magneton number (n{sub B}) for ZMMFO could be very well explained by Localized canting of spin (LCS) model while Random canting of spin (RCS) model was used for MACFO system.« less

A study of Na(x)Pt3O4 as an O2 electrode bifunctional electrocatalyst

NASA Technical Reports Server (NTRS)

Fielder, William L.; Singer, Joseph

1991-01-01

The present study suggests that polytetrafluoroethylene (PTFE) bonded Na(X)Pt3O4 gas porous diffusion electrodes may be a viable candidate for bifunctional O2 reduction and evolution activity. The electrodes exhibited Tafel slopes of about 0.06 V/decade for both O2 reduction an evolution. For O2 reduction, the 0.06 slope doubled to 0.12 V/decade at larger current densities. Preliminary stability testing at 24 C suggest that the Na(x)Pt3O4 electrodes were relatively stable at reducing and oxidizing potentials typically encountered at the O2 electrodes in a regenerative fuel cell.

Effect of chemical pressure on the electronic phase transition in Ca 1-x Sr x Mn 7 O 12 films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huon, A.; Lee, D.; Herklotz, A.

Here, we demonstrate how chemical pressure affects the structural and electronic phase transitions of the quadruple perovskite CaMn 7O 12 by Sr doping, a compound that exhibits a charge-ordering transition above room temperature making it a candidate for oxide electronics. We also have synthesized Ca 1-xSr xMn 7O 12 (0 ≤ x ≤ 0.6) thin films by oxide molecular beam epitaxy on (LaAlO 3) 0.3(SrAl 0.5Ta 0.5O 3) 0.7 (LSAT) substrates. The substitution of Sr for Ca results in a linear expansion of the lattice, as revealed by X-ray diffraction. Temperature-dependent resistivity and X-ray diffraction measurements are used to demonstratemore » that the coupled charge-ordering and structural phase transitions can be tuned with Sr doping. An increase in Sr concentration acts to decrease the phase transition temperature (T*) from 426 K at x = 0 to 385 K at x = 0.6. Furthemore, the presence of a tunable electronic phase transition, above room temperature, points to the potential applicability of Ca 1-xSr xMn 7O 12 in sensors or oxide electronics, for example, via charge doping.« less

Effect of chemical pressure on the electronic phase transition in Ca 1-x Sr x Mn 7 O 12 films

DOE PAGES

Huon, A.; Lee, D.; Herklotz, A.; ...

2017-09-18

Here, we demonstrate how chemical pressure affects the structural and electronic phase transitions of the quadruple perovskite CaMn 7O 12 by Sr doping, a compound that exhibits a charge-ordering transition above room temperature making it a candidate for oxide electronics. We also have synthesized Ca 1-xSr xMn 7O 12 (0 ≤ x ≤ 0.6) thin films by oxide molecular beam epitaxy on (LaAlO 3) 0.3(SrAl 0.5Ta 0.5O 3) 0.7 (LSAT) substrates. The substitution of Sr for Ca results in a linear expansion of the lattice, as revealed by X-ray diffraction. Temperature-dependent resistivity and X-ray diffraction measurements are used to demonstratemore » that the coupled charge-ordering and structural phase transitions can be tuned with Sr doping. An increase in Sr concentration acts to decrease the phase transition temperature (T*) from 426 K at x = 0 to 385 K at x = 0.6. Furthemore, the presence of a tunable electronic phase transition, above room temperature, points to the potential applicability of Ca 1-xSr xMn 7O 12 in sensors or oxide electronics, for example, via charge doping.« less

High temperature transport properties of co-substituted Ca{sub 1−x}Ln{sub x}Mn{sub 1−x}Nb{sub x}O{sub 3} (Ln = Yb, Lu; 0.02 ≤ x ≤ 0.08)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nag, Abanti, E-mail: abanti@nal.res.in; Bose, Rapaka S.C.

Highlights: • The thermoelectric Ca{sub 1−x}Ln{sub x}Mn{sub 1−x}Nb{sub x}O{sub 3} (Ln = Yb, Lu) perovskite are prepared by solid state reaction. • The high temperature transport properties are explored. • The co-substituted Ca{sub 1−x}Ln{sub x}Mn{sub 1−x}Nb{sub x}O{sub 3} shows non-metal-like temperature dependence of resistivity. • The Seebeck coefficient of Ca{sub 1−x}Ln{sub x}Mn{sub 1−x}Nb{sub x}O{sub 3} exhibits metallic nature. • The puzzling transport phenomenon is originated from oxygen vacancy related defect centres. - Abstract: The co-substituted Ca{sub 1−x}Ln{sub x}Mn{sub 1−x}Nb{sub x}O{sub 3} (Ln = Yb, Lu; 0.02 ≤ x ≤ 0.08) are synthesized by solid-state reaction and the electronic transport propertiesmore » are investigated. Rietveld refinement confirms the formation of single phase orthorhombic structure with gradual increase of cell parameters with doping level. The electronic transport properties such as Seebeck coefficient and electrical resistivity decrease with increasing the dopant concentration for both the co-substituted compositions. All the compositions of Ca{sub 1−x}Ln{sub x}Mn{sub 1−x}Nb{sub x}O{sub 3} show nonmetal-like temperature dependence of resistivity; whereas metal-like temperature dependence of thermopower. This inconsistency is explained by the formation of oxygen vacancy associated defect centres that originates from partial reduction of Mn{sup 4+} to Mn{sup 3+} due to co-substitution. The defect centres act as extrinsic carriers and cause additional contribution to the entropy of the system, leading to increase of Seebeck coefficient as a function of temperature. The transport mechanism of charge carriers is explained in the framework of Mott’s small polaron hopping mechanism.« less

Effect of high-pressure H{sub 2}O treatment on elimination of interfacial GeO{sub X} layer between ZrO{sub 2} and Ge stack

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Chen-Shuo; Liu, Po-Tsun

2011-08-22

This investigation demonstrates the effect of high-pressure H{sub 2}O treatment on the elimination of the interfacial germanium suboxide (GeO{sub X}) layer between ZrO{sub 2} and Ge. The formation of GeO{sub X} interlayer increases the gate-leakage current and worsen the controllability of the gate during deposition or thermal cycles. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy reveal that high-pressure H{sub 2}O treatment eliminates the interfacial GeO{sub X} layer. The physical mechanism involves the oxidation of non-oxidized Zr with H{sub 2}O and the reduction of GeO{sub X} by H{sub 2}. Treatment with H{sub 2}O reduces the gate-leakage current of a ZrO{submore » 2}/Ge capacitor by a factor of 1000.« less

Structural stability, enhanced magnetic, piezoelectric, and transport properties in (1-x)BiFeO3-(x)Ba0.70Sr0.30TiO3 nanoparticles

NASA Astrophysics Data System (ADS)

Sharma, Subhash; Singh, Vikash; Anshul, Avneesh; Siqueiros, J. M.; Dwivedi, R. K.

2018-05-01

Multiferroic samples with composition (1-x)BiFeO3-(x)(Ba0.70Sr0.30)TiO3 (BFO-BST) were synthesized using a sol-gel route to study the effect of BST doping on structural, transport, and magnetic properties in BiFeO3 (BFO). X-ray diffraction studies with Rietveld analysis revealed that a phase transition occurred from rhombohedral (R3c) (0.0 ≤ × ≤ 0.15) to tetragonal (P4 mm) for x = 0.20 and nanocrystalline nature confirmed by transmission electron microscopy measurements. Piezoelectric properties improved as x increased from x = 0.0 (58 pC/N) to x = 0.20 (112 pC/N) increasing distortion in the crystal structure as evinced by Williamson-Hall analysis. Ferromagnetism was observed in doped BFO, different from the antiferromagnetic ordering in bulk BFO, indicating the noteworthy size effects and Fe-O-Fe bond angle variations in the magnetic ordering of BFO. An improvement in ferroelectric properties is observed with doping of BST compared to pristine BFO. Thermally activated conduction behavior occurred at low and high temperature regions as revealed by temperature dependent dc resistivity measurement. Effective improvements in dielectric response, meaning high dielectric constant with a low dielectric loss, were found in the doped samples.

A highly active and stable IrO x/SrIrO 3 catalyst for the oxygen evolution reaction

DOE PAGES

Seitz, Linsey C.; Dickens, Colin F.; Nishio, Kazunori; ...

2016-09-02

Oxygen electrochemistry plays a key role in renewable energy technologies such as fuel cells and electrolyzers, but the slow kinetics of the oxygen evolution reaction (OER) limit the performance and commercialization of such devices. Here we report an iridium oxide/strontium iridium oxide (IrO x/SrIrO 3) catalyst formed during electrochemical testing by strontium leaching from surface layers of thin films of SrIrO 3. This catalyst has demonstrated specific activity at 10 milliamps per square centimeter of oxide catalyst (OER current normalized to catalyst surface area), with only 270 to 290 millivolts of overpotential for 30 hours of continuous testing in acidicmore » electrolyte. Here, density functional theory calculations suggest the formation of highly active surface layers during strontium leaching with IrO 3 or anatase IrO 2 motifs. The IrO x/SrIrO 3 catalyst outperforms known IrO x and ruthenium oxide (RuO x) systems, the only other OER catalysts that have reasonable activity in acidic electrolyte.« less

Interfacial RhO{sub x}/CeO{sub 2} sites as locations for low temperature N{sub 2}O dissociation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cunningham, J.; Hickey, J.N.; Soria, J.

Temperatures required for extensive N{sub 2}O dissociation to N{sub 2}, or to N{sub 2} plus O{sub 2}, over 0.5% RhO{sub x}/CeO{sub 2} materials, and over polycrystalline Rh{sub 2}O{sub 3} or CeO{sub 2}, are compared for preoxidised and for prereduced samples on the basis of conversions achieved in pulsed-reactant, continuous-flow and recirculatory microcatalytic reactors. Influences of sample prereduction or preoxidation upon those measurements and upon results from parallel ESR and FTIR studies of N{sub 2}O interactions with such materials are presented and compared. Over partially reduced 0.5% RhO{sub x}/CeO{sub 2} materials complete dissociation of N{sub 2}O pulses to N{sub 2} plusmore » O{sub 2} is obtained at temperatures 50-100{degrees} lower than those required for extensive dissociation over prereduced Rh{sub 2}O{sub 3}. Furthermore, N{sub 2} was the sole product from the latter. Higher ongoing N{sub 2}O conversions to N{sub 2} plus O{sub 2} at 623 K over 0.5% Rh/CeO{sub 2} in pulsed-reactant than in continuous-flow mode point to regeneration of active sites under helium flushing between pulses. The TPD profile for dioxygen release from Rhodia containing samples at temperatures 350-550 K is presented. ESR measurements reveal complementary effects of outgassings at temperatures, T{sub v}, {ge} 573 K upon the availability at RhO{sub x}/CeO{sub 2} surfaces of electron-excess sites reactive towards N{sub 2}O. Differences from observations over Rh{sub 2}O{sub 3} and CeO{sub 2} can be understood by attributing the low-temperature activity of RhO{sub x}/CeO{sub 2} to electron excess sites at microinterfaces between the dispersed Rhodia component and the Ceria support.« less

β-(Al{sub x}Ga{sub 1−x}){sub 2}O{sub 3}/Ga{sub 2}O{sub 3} (010) heterostructures grown on β-Ga{sub 2}O{sub 3} (010) substrates by plasma-assisted molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaun, Stephen W., E-mail: skaun@umail.ucsb.edu; Wu, Feng; Speck, James S.

2015-07-15

By systematically changing growth parameters, the growth of β-(Al{sub x}Ga{sub 1−x}){sub 2}O{sub 3}/Ga{sub 2}O{sub 3} (010) heterostructures by plasma-assisted molecular beam epitaxy was optimized. Through variation of the Al flux under O-rich conditions at 600 °C, β-(Al{sub x}Ga{sub 1−x}){sub 2}O{sub 3} (010) layers spanning ∼10% to ∼18% Al{sub 2}O{sub 3} were grown directly on β-Ga{sub 2}O{sub 3} (010) substrates. Nominal β-(Al{sub x}Ga{sub 1−x}){sub 2}O{sub 3} (010) compositions were determined through Al:Ga flux ratios. With x = ∼0.18, the β-(Al{sub x}Ga{sub 1−x}){sub 2}O{sub 3} (020) layer peak in a high-resolution x-ray diffraction (HRXRD) ω-2θ scan was barely discernible, and Pendellösung fringes were not visible.more » This indicated that the phase stability limit of Al{sub 2}O{sub 3} in β-Ga{sub 2}O{sub 3} (010) at 600 °C was less than ∼18%. The substrate temperature was then varied for a series of β-(Al{sub ∼0.15}Ga{sub ∼0.85}){sub 2}O{sub 3} (010) layers, and the smoothest layer was grown at 650 °C. The phase stability limit of Al{sub 2}O{sub 3} in β-Ga{sub 2}O{sub 3} (010) appeared to increase with growth temperature, as the β-(Al{sub x}Ga{sub 1−x}){sub 2}O{sub 3} (020) layer peak with x = ∼0.18 was easily distinguishable by HRXRD in a sample grown at 650 °C. Cross-sectional transmission electron microscopy (TEM) indicated that β-(Al{sub ∼0.15}Ga{sub ∼0.85}){sub 2}O{sub 3} (010) layers (14.4% Al{sub 2}O{sub 3} by energy dispersive x-ray spectroscopy) grown at 650 °C were homogeneous. β-(Al{sub ∼0.20}Ga{sub ∼0.80}){sub 2}O{sub 3} (010) layers, however, displayed a phase transition. TEM images of a β-(Al{sub ∼0.15}Ga{sub ∼0.85}){sub 2}O{sub 3}/Ga{sub 2}O{sub 3} (010) superlattice grown at 650 °C showed abrupt layer interfaces and high alloy homogeneity.« less

Electronic structures of anatase (TiO2)1-x(TaON)x solid solutions: a first-principles study.

PubMed

Dang, Wenqiang; Chen, Hungru; Umezawa, Naoto; Zhang, Junying

2015-07-21

Sensitizing wide band gap photo-functional materials under visible-light irradiation is an important task for efficient solar energy conversion. Although nitrogen doping into anatase TiO2 has been extensively studied for this purpose, it is hard to increase the nitrogen content in anatase TiO2 because of the aliovalent nitrogen substituted for oxygen, leading to the formation of secondary phases or defects that hamper the migration of photoexcited charge carriers. In this paper, electronic structures of (TiO2)1-x(TaON)x (0 ≤ x ≤ 1) solid solutions, in which the stoichiometry is satisfied with the co-substitution of Ti for Ta along with O for N, are investigated within the anatase crystal structure using first-principles calculations. Our computational results show that the solid solutions have substantially narrower band gaps than TiO2, without introducing any localized energy states in the forbidden gap. In addition, in comparison with the pristine TiO2, the solid solution has a direct band gap when the content of TaON exceeds 0.25, which is advantageous to light absorption. The valence band maximum (VBM) of the solid solutions, which is mainly composed of N 2p states hybridized with O 2p, Ti 3d or Ta 5d orbitals, is higher in energy than that of pristine anatase TiO2 consisting of non-bonding O 2p states. On the other hand, incorporating TaON into TiO2 causes the formation of d-d bonding states through π interactions and substantially lowers the conduction band minimum (CBM) because of the shortened distance between some metal atoms. As a result, the anatase (TiO2)1-x(TaON)x is expected to become a promising visible-light absorber. In addition, some atomic configurations are found to possess exceptionally narrow band gaps.

Bipolar resistance switching in Pt/CuO x /Pt via local electrochemical reduction

DOE PAGES

D'Aquila, Kenneth; Phatak, Charudatta; Holt, Martin V.; ...

2014-06-17

We investigated the local changes in copper oxidation state and the corresponding resistance changes in Pt/CuO x/Pt nanoscale heterostructures using x-ray nanoprobe spectro-microscopy and current-voltage characterization. After gentle electroforming, during which the current-voltage behavior remains non-linear, the low resistance state was reached, and we also observed regions of 160 nm width that show an increase in Cu K-alpha fluorescence intensity, indicative of partial reduction of the CuO x. Analysis of the current voltage curves showed that the dominant conduction mechanism is Schottky emission and that the resistance state is correlated with the Schottky barrier height. We also propose that themore » reversible resistivity change in these Pt/CuO x/Pt heterostructures occurs through local electrochemical reduction leading to change of the Schottky barrier height at the interface between Pt and the reduced CuO x layers and to change of the CuO x resistivity within laterally confined portions of the CuO x layer. Our experiments reveal important insights into the mechanism of resistance switching of Pt/CuO x/Pt performed in a current and voltage regime that does not create a metallic conduction path.« less

Analysis of SAW properties in ZnO/AlxGa1-xN/c-Al2O3 structures.

PubMed

Chen, Ying; Emanetoglu, Nuri William; Saraf, Gaurav; Wu, Pan; Lu, Yicheng; Parekh, Aniruddh; Merai, Vinod; Udovich, Eric; Lu, Dong; Lee, Dong S; Armour, Eric A; Pophristic, Milan

2005-07-01

Piezoelectric thin films on high acoustic velocity nonpiezoelectric substrates, such as ZnO, AlN, or GaN deposited on diamond or sapphire substrates, are attractive for high frequency and low-loss surface acoustic wave devices. In this work, ZnO films are deposited on AlxGa1-xN/c-Al2O3 (0 < or = chi < or = 1) substrates using the radio frequency (RF) sputtering technique. In comparison with a single AlxGa1-xN layer deposited on c-Al2O3 with the same total film thickness, a ZnO/AlxGa1-xN/c-Al2O3 multilayer structure provides several advantages, including higher order wave modes with higher velocity and larger electromechanical coupling coefficient (K2). The surface acoustic wave (SAW) velocities and coupling coefficients of the ZnO/AlxGa1-xN/c-Al2O3 structure are tailored as a function of the Al mole percentage in AlxGa1-xN films, and as a function of the ZnO (h1) to AlxGa1-xN (h2) thickness ratio. It is found that a wide thickness-frequency product (hf) region in which coupling is close to its maximum value, K(2)max, can be obtained. The K(2)max of the second order wave mode (h1 = h2) is estimated to be 4.3% for ZnO/GaN/c-Al2O3, and 3.8% for ZnO/AlN/c-Al2O3. The bandwidth of second and third order wave modes, in which the coupling coefficient is within +/- 0.3% of K(2)max, is calculated to be 820 hf for ZnO/GaN/c-Al2O3, and 3620 hf for ZnO/AlN/c-Al2O3. Thus, the hf region in which the coupling coefficient is close to the maximum value broadens with increasing Al content, while K(2)max decreases slightly. When the thickness ratio of AlN to ZnO increases, the K(2)max and hf bandwidth of the second and third higher wave modes increases. The SAW test devices are fabricated and tested. The theoretical and experimental results of velocity dispersion in the ZnO/AlxGa1-xN/c-Al2O3 structures are found to be well matched.

Ultrathin TiO(x) films on Pt(111): a LEED, XPS, and STM investigation.

PubMed

Sedona, Francesco; Rizzi, Gian Andrea; Agnoli, Stefano; Llabrés i Xamena, Francesc X; Papageorgiou, Anthoula; Ostermann, Dieter; Sambi, Mauro; Finetti, Paola; Schierbaum, Klaus; Granozzi, Gaetano

2005-12-29

Ultrathin ordered titanium oxide films on Pt(111) surface are prepared by reactive evaporation of Ti in oxygen. By varying the Ti dose and the annealing conditions (i.e., temperature and oxygen pressure), six different long-range ordered phases are obtained. They are characterized by means of low-energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). By careful optimization of the preparative parameters, we find conditions where predominantly single phases of TiO(x), revealing distinct LEED pattern and STM images, are produced. XPS binding energy and photoelectron diffraction (XPD) data indicate that all the phases, except one (the stoichiometric rect-TiO2), are one monolayer thick and composed of a Ti-O bilayer with interfacial Ti. Atomically resolved STM images confirm that these TiO(x) phases wet the Pt surface, in contrast to rect-TiO2. This indicates their interface stabilization. At a low Ti dose (0.4 monolayer equivalents, MLE), an incommensurate kagomé-like low-density phase (k-TiO(x) phase) is observed where hexagons are sharing their vertexes. At a higher Ti dose (0.8 MLE), two denser phases are found, both characterized by a zigzag motif (z- and z'-TiO(x) phases), but with distinct rectangular unit cells. Among them, z'-TiO(x), which is obtained by annealing in ultrahigh vacuum (UHV), shows a larger unit cell. When the postannealing of the 0.8 MLE deposit is carried out at high temperatures and high oxygen partial pressures, the incommensurate nonwetting, fully oxidized rect-TiO2 is found The symmetry and lattice dimensions are almost identical with rect-VO2, observed in the system VO(x)/Pd(111). At a higher coverage (1.2 MLE), two commensurate hexagonal phases are formed, namely the w- [(square root(43) x square root(43)) R 7.6 degrees] and w'-TiO(x) phase [(7 x 7) R 21.8 degrees]. They show wagon-wheel-like structures and have slightly different lattice dimensions. Larger Ti deposits

Enhanced room temperature multiferroic characteristics in hexagonal LuFe1-xNixO3 (x = 0 - 0.3) nanoparticles

NASA Astrophysics Data System (ADS)

Suresh, Pittala; Vijaya Laxmi, K.; Anil Kumar, P. S.

2018-02-01

Single phase polycrystalline LuFe1-xNixO3 (x = 0 - 0.3) (LFNO) nanoparticles are synthesized using the sol-gel method. X-ray diffraction measurements revealed that the crystal structure of Ni-doped samples is isomorphic to hexagonal LuFeO3 (LFO). The phase pure hexagonal P63cm symmetry exists for 0 ≤ x ≤ 0.3, and the secondary phases appear for x ≥ 0.4. Raman spectra show a shift in the mode frequency corresponding to the changes in Lu-O and Fe-O bond lengths with Ni doping. An enhancement in the magnetization is observed for LFNO throughout the temperature range (400-5 K) compared to LFO. The antiferromagnetic state of LFO becomes ferrimagnetic at low temperatures, and a net magnetization is observed at room temperature with Ni doping. As Ni concentration increases, a systematic increment in the ferroelectric polarization is observed. This enhancement in polarization is believed to be due to the distortion in FeO5 cage, while the improvement in magnetic properties is due to the induced magnetic interactions, caused by the Fe-Ni interactions on the triangular lattice with Ni doping in LuFeO3.

ALD TiO x as a top-gate dielectric and passivation layer for InGaZnO115 ISFETs

NASA Astrophysics Data System (ADS)

Pavlidis, S.; Bayraktaroglu, B.; Leedy, K.; Henderson, W.; Vogel, E.; Brand, O.

2017-11-01

The suitability of atomic layer deposited (ALD) titanium oxide (TiO x ) as a top gate dielectric and passivation layer for indium gallium zinc oxide (InGaZnO115) ion sensitive field effect transistors (ISFETs) is investigated. TiO x is an attractive barrier material, but reports of its use for InGaZnO thin film transistor (TFT) passivation have been conflicting thus far. In this work, it is found that the passivated TFT’s behavior depends on the TiO x deposition temperature, affecting critical device characteristics such as threshold voltage, field-effect mobility and sub-threshold swing. An O2 annealing step is required to recover TFT performance post passivation. It is also observed that the positive bias stress response of the passivated TFTs improves compared the original bare device. Secondary ion mass spectroscopy excludes the effects of hydrogen doping and inter-diffusion as sources of the temperature-dependent performance change, therefore indicating that oxygen gettering induced by TiO x passivation is the likely source of oxygen vacancies and, consequently, carriers in the InGaZnO film. It is also shown that potentiometric sensing using ALD TiO x exhibits a near Nernstian response to pH change, as well as minimizes V TH drift in TiO x passivated InGaZnO TFTs immersed in an acidic liquid. These results add to the understanding of InGaZnO passivation effects and underscore the potential for low-temperature fabricated InGaZnO ISFETs to be used as high-performance mobile chemical sensors.

Chemical thermodynamic representation of (U, Pu, Am)O 2- x

NASA Astrophysics Data System (ADS)

Osaka, Masahiko; Namekawa, Takashi; Kurosaki, Ken; Yamanaka, Shinsuke

2005-09-01

The oxygen potential isotherms of (U, Pu, Am)O 2- x were represented by a chemical thermodynamic model proposed by Lindemer et al. It was assumed in the present model that (U, Pu, Am)O 2- x consisted of the chemical species [UO 2], [PuO 2], [Pu 4/3O 2], [AmO 2] and [Am 5/4O 2] in a pseudo-quaternary system by treating the reduction rates of Pu and Am as identical; furthermore an interaction between [Am 5/4O 2] and [UO 2] was introduced. The agreement between analytical and experimental isotherms was good, but the analytical values slightly overestimated the experimental values especially in the case of lower Am content. Adding an interaction between [Am 5/4O 2] and [PuO 2] to the model resulted in a better representation.

Remote interfacial dipole scattering and electron mobility degradation in Ge field-effect transistors with GeO x /Al2O3 gate dielectrics

NASA Astrophysics Data System (ADS)

Wang, Xiaolei; Xiang, Jinjuan; Wang, Shengkai; Wang, Wenwu; Zhao, Chao; Ye, Tianchun; Xiong, Yuhua; Zhang, Jing

2016-06-01

Remote Coulomb scattering (RCS) on electron mobility degradation is investigated experimentally in Ge-based metal-oxide-semiconductor field-effect-transistors (MOSFETs) with GeO x /Al2O3 gate stacks. It is found that the mobility increases with greater GeO x thickness (7.8-20.8 Å). The physical origin of this mobility dependence on GeO x thickness is explored. The following factors are excluded: Coulomb scattering due to interfacial traps at GeO x /Ge, phonon scattering, and surface roughness scattering. Therefore, the RCS from charges in gate stacks is studied. The charge distributions in GeO x /Al2O3 gate stacks are evaluated experimentally. The bulk charges in Al2O3 and GeO x are found to be negligible. The density of the interfacial charge is  +3.2  ×  1012 cm-2 at the GeO x /Ge interface and  -2.3  ×  1012 cm-2 at the Al2O3/GeO x interface. The electric dipole at the Al2O3/GeO x interface is found to be  +0.15 V, which corresponds to an areal charge density of 1.9  ×  1013 cm-2. The origin of this mobility dependence on GeO x thickness is attributed to the RCS due to the electric dipole at the Al2O3/GeO x interface. This remote dipole scattering is found to play a significant role in mobility degradation. The discovery of this new scattering mechanism indicates that the engineering of the Al2O3/GeO x interface is key for mobility enhancement and device performance improvement. These results are helpful for understanding and engineering Ge mobility enhancement.

Constructing hierarchical interfaces: TiO 2-supported PtFe-FeO x nanowires for room temperature CO oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Huiyuan; Wu, Zili; Dong, Su

2015-08-05

This is a report of a facile approach to constructing catalytic active hierarchical interfaces in one-dimensional (1D) nanostructure, exemplified by the synthesis of TiO 2-supported PtFe–FeO x nanowires (NWs). The hierarchical interface, constituting atomic level interactions between PtFe and FeO x within each NW and the interactions between NWs and support (TiO 2), enables CO oxidation with 100% conversion at room temperature. We identify the role of the two interfaces by probing the CO oxidation reaction with isotopic labeling experiments. Both the oxygen atoms (Os) in FeO x and TiO 2 participate in the initial CO oxidation, facilitating the reactionmore » through a redox pathway. Moreover, the intact 1D structure leads to the high stability of the catalyst. After 30 h in the reaction stream, the PtFe–FeO x/TiO2 catalyst exhibits no activity decay. These results provide a general approach and new insights into the construction of hierarchical interfaces for advanced catalysis.« less

Facile synthesis of Cu/Cu{sub x}O nanoarchitectures with adjustable phase composition for effective NO{sub x} gas sensor at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Lixue; Li, Li; Yang, Ying

2013-10-15

Graphical abstract: The Cu/Cu{sub x}O nanoarchitectures with 30–70 nm hollow nanospheres reduced by 3 mmol NaBH{sub 4} exhibits excellent gas-sensing property to low-concentration NO{sub x} gas at room temperature. - Highlights: • The Cu/Cu{sub x}O nanoarchitectures with hollow nanospheres are successfully synthesized. • The method is used for preparing the with Cu/Cu{sub x}O adjustable phase composition. • The C3 sample exhibites excellent gas-sensing propertie to NO{sub x} at room temperation. • The Cu/Cu{sub x}O nanoarchitectures have significant for application of gas sensor. - Abstract: The Cu/Cu{sub x}O nanoarchitectures with 30–70 nm hollow nanospheres are successfully synthesized by a facile wetmore » chemical method. The synthesized products have been studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermo gravimetric-differential scanning calorimetry (TG-DSC) analysis. The Cu/Cu{sub x}O sensors based on the nanoarchitectures are used to detect the NO{sub x} at room temperature. The results demonstrate that the obtained Cu/Cu{sub x}O nanoarchitectures reduced by 3 mmol NaBH{sub 4} exhibits excellent gas-sensing properties: low detection limit of 0.97 ppm, relatively high sensitivity, short response time, broad linear range and high selectivity. The reasons for gas-sensing activity enhancement on Cu/Cu{sub x}O nanoarchitectures are discussed. The Cu/Cu{sub x}O nanocrystalline with the hierarchical pores structure and tunable compositions have significant for application of gas sensor.« less

Thermoelectric Power Measurements of xSb-(60- x)V2O5-40TeO2 Glasses

NASA Astrophysics Data System (ADS)

Souri, Dariush; Siahkali, Zahra; Moradi, Mohammad

2016-01-01

Bulk xSb-(60- x)V2O5-40TeO2 glass systems (with 0 ≤ x ≤ 15 in mol.%) were prepared by using the standard melt quenching procedure, and their Seebeck coefficients, S, were measured within the temperature range of 250-470 K. For the understudied samples, the thermoelectric powers at typical temperatures of 296 K, 370 K and 407 K were measured, and were in the ranges (-405) to (-698) μVK-1, (-394) to (-685) μVK-1 and (-392) to (-691) μVK-1, respectively. The selection of typical temperatures aims at the evaluation of the trend of figure of merit in these glasses. Based on the negative sign of S, the present glasses were found to be n-type semiconductors; also, the experimental relationship between S and C V ( C V = [V4+]/ V tot is the ratio of the content of reduced vanadium ions) satisfied the theoretical Heikes formula, relating S to ln( C V/1 - C V), and also the Mackenzie formula, relating S to ln([V5+]/[V4+]). The parameter α^' in Heikes formula was determined to be ≪1 and so the small polaron hopping conduction mechanism was certified to occur in these glasses; this result confirms the previously reported results of direct current (DC) electrical conduction experiments on the same samples. Results of thermoelectric measurements show the compositional dependence of S on Sb content and C V, indicating that S increases with the increase in Sb content; these results show that the dominant factor determining S is C V. Also, figure of merit was determined for these glasses, which show the highest value for 60V2O5-40TeO2 glass system, as a good candidate in thermoelectric applications.

Antiferromagnetic-ferromagnetic crossover in UO 2-TiO x multi-phase systems

NASA Astrophysics Data System (ADS)

Nakamura, Akio; Tsutsui, Satoshi; Yoshii, Kenji

2001-05-01

An antiferromagnetic (AF)-weakly ferromagnetic (WF) crossover has been found for UO 2-TiO x multi-phase systems, (1- y)UO 2+ yTiO x ( y=0.05-0.72, x=0, 1.0, 1.5 and 2.0), when these mixtures are heat treated at high temperature in vacuum. From the powder X-ray diffraction and electron-microprobe analyses, their phase assemblies were as follows: for x=0, 1.0 and 1.5, a heterogeneous two-phase mixture of UO 2+TiO x; for x=2.0, that of UO 2+UTi 2O 6 for y<0.67, showing characteristic microstructures, and for y>0.67 that of UTi 2O 6+TiO 2 (plus residual minor UO 2). Magnetic susceptibility ( χ) of the present UO 2 powder was confirmed to exhibit an antiferromagnetic sharp drop at TN (=30.5 K). In contrast, χ of these multi-phase systems was found to exhibit a sharp upturn at the respective TN, while their TN values remained almost constant with varying y. This χ upturn at TN is most pronounced for UO 2+Ti-oxide (titania) systems ( x=1.0, 1.5 and 2.0) over the wide mixture ratio above y˜0.10. These observations indicate that an AF-WF crossover is induced for these multi-phase systems, plausibly due to the interfacial magnetic modification of UO 2 in contact with the oxide partners.

Composite CuFe1 - xSnxO2/p-type silicon photodiodes

NASA Astrophysics Data System (ADS)

Al-Sehemi, Abdullah G.; Mensah-Darkwa, K.; Al-Ghamdi, Ahmed A.; Soylu, M.; Gupta, R. K.; Yakuphanoglu, F.

2017-06-01

CuFe1 - xSnxO2 composite thin film/p-type silicon diodes were prepared on substrate by sol-gel method (x = 0.00, 0.01, 0.03, 0.05, 0.07). The structure of CuFe1 - xSnxO2 composite thin films was studied using XRD analysis and films exhibited amorphous behavior. The elemental compositions and surface morphology of the films were characterized using SEM and EDX. EDX results confirmed the presence of the compositional elements. The optical band gap of CuFe1 - xSnxO2 composite thin films was determined using the optic spectra. The optical band gaps of the CuFe1 - xSnxO2 composite thin films were calculated using optical data and were found to be 3.75, 3.78, 3.80, 3.85 and 3.83 eV for x = 0.00, 0.01, 0.03, 0.05 and 0.07, respectively. The photoresponse and electrical properties of the Al/CuFe1 - xSnxO2/p-Si/Al diode were studied. The barrier height and ideality factor were determined to be averagely 0.67 eV and 2.6, respectively. The electrical and photoresponse characteristics of the diodes have been investigated under dark and solar light illuminations, respectively. The interface states were used to explain the results obtained in present study. CuFe1 - xSnxO2 photodiodes exhibited a high photoresponsivity to be used in optoelectronic applications.

Piezoelectric properties of nonstoichiometric Sr1-xBi2+2x/3Ta2O9 ceramics

NASA Astrophysics Data System (ADS)

Jain, Rajni; Chauhan, Arun Kumar Singh; Gupta, Vinay; Sreenivas, K.

2005-06-01

The effect of poling on the structural, dielectric, and piezoelectric properties has been investigated for sol-gel-derived strontium bismuth tantalate (SBT) [Sr1-xBi2+2x/3Ta2O9] ceramics with x =0.0,0.15,0.30,0.45. The dielectric and ferroelectric properties are found to improve with increase in x up to 0.3. Beyond x >0.3 the properties are found to degrade due to the limited solid solubility and the presence of a mixed phase of bismuth tantalate (BiTaO4) is detected with x =0.45. Poling treatment reduces the dielectric dispersion and dielectric loss in the frequency range (0.1-100kHz). The resonance and antiresonance frequencies increase with increase in x (x=0-0.30), and the corresponding minimum impedance decreases. The measured coupling coefficients (kp) are small (0.0967-0.1) for x =0-0.30, and the electromechanical quality factor (Qm=915) is a maximum for the Sr0.7Bi2.2Ta2O9 composition (x=0.30). The estimated piezoelectric charge coefficient (d31) and piezoelectric voltage coefficient (g31) are 5.2pC/N and 5.8×10-3Vm/N, respectively. The positive values of d31 and g31 and the low dielectric permittivity of SBT yield a high value for the hydrostatic coefficients, despite the low charge coefficient of d33=24pC/N. The maximum values of charge coefficient (dh=34pC/N) and voltage coefficient (gh=39×10-3Vm/N) are obtained for Sr0.7Bi2.2Ta2O9 composition, and the estimated hydrostatic figure of merit (dhgh×10-15=1215m2/N) is high.

Unraveling the mechanism of ultraviolet-induced optical gating in Zn1-x Mg x O nanocrystal solid solution field effect transistors

NASA Astrophysics Data System (ADS)

Kim, Youngjun; Cho, Seongeun; Park, Byoungnam

2018-03-01

We report ultraviolet (UV)-induced optical gating in a Zn1-x Mg x O nanocrystal solid solution (NCSS) field effect transistor (FET) through a systematic study in which UV-induced charge transport properties are probed as a function of Mg composition. Change in the electrical properties of Zn1-x Mg x O NCSS associated with electronic traps is investigated by field effect-modulated current-voltage characteristic curves in the dark and under illumination. Under UV illumination, significant threshold voltage shift to a more negative value in an n-channel Zn1-x Mg x O NCSS FET is observed. Importantly, as the Mg composition increases, the effect of UV illumination on the threshold voltage shift is alleviated. We found that threshold voltage shift as a function of Mg composition in the dark and under illumination is due to difference in the deep trap density in the Zn1-x Mg x O NCSS. This is supported by Mg composition dependent photoluminescence intensity in the visible range and reduced FET mobility with Mg addition. The presence of the deep traps and the corresponding trap energy levels in the Zn1-x Mg x O NCSS are ensured by photoelectron spectroscopy in air.

Dynamic response performance of proton exchange membrane fuel cell stack with Pt/C-RuO2·xH2O electrode

NASA Astrophysics Data System (ADS)

Lu, Lu; Xu, Hongfeng; Zhao, Hong; Sun, Xin; Dong, Yiming; Ren, Ruiming

2013-11-01

The dynamic response performance of a proton exchange membrane fuel cell (PEMFC) significantly affects its durability and reliability. Thus, the improvement of the dynamic performance of PEMFC has become the key for prolonging the PEMFC life in fuel cell vehicle applications. In this study, RuO2·xH2O is prepared by sol-gel method, and then sprayed onto catalyst layers to promote PEMFC dynamic response performance. The prepared RuO2·xH2O is characterized by TEM, which shows that the average particle size of RuO2·xH2O is 8 nm and that the particulates are uniformly distributed. A 10-cell stack is assembled using membrane electrode assembly (MEA) with and without RuO2·xH2O. This stack is studied under various loading cycles and operating conditions, including different air stoichiometries, relative humidities, and loading degrees. Results show that the steady-state performance of the MEA with RuO2·xH2O is better than that in the MEA without RuO2·xH2O with a decreasing relative humidity from 80% to 20%. A slower and more unstable dynamic response of the MEA without RuO2·xH2O is observed as air stoichiometry and relative humidity decrease as well as the loading increase. Thus, RuO2·xH2O improves the dynamic response performance, indicating that RuO2·xH2O can buffer the voltage undershoot, improve the stability, and prolong the lifetime of the PEMFC stack.

Giant Faraday rotation in Bi(x)Ce(3-x)Fe5O12 epitaxial garnet films.

PubMed

Chandra Sekhar, M; Singh, Mahi R; Basu, Shantanu; Pinnepalli, Sai

2012-04-23

Thin films of Bi(x)Ce(3-x)Fe(5)O(12) with x = 0.7 and 0.8 compositions were prepared by using pulsed laser deposition. We investigated the effects of processing parameters used to fabricate these films by measuring various physical properties such as X-ray diffraction, transmittance, magnetization and Faraday rotation. In this study, we propose a phase diagram which provides a suitable window for the deposition of Bi(x)Ce(3-x)Fe(5)O(12) epitaxial films. We have also observed a giant Faraday rotation of 1-1.10 degree/µm in our optimized films. The measured Faraday rotation value is 1.6 and 50 times larger than that of CeYIG and YIG respectively. A theoretical model has been proposed for Faraday rotation based on density matrix method and an excellent agreement between experiment and theory is found. © 2012 Optical Society of America

Concurrent ionic migration and electronic effects at the memristive TiO x /La1/3Ca2/3MnO3-x interface

NASA Astrophysics Data System (ADS)

Román Acevedo, W.; Ferreyra, C.; Sánchez, M. J.; Acha, C.; Gay, R.; Rubi, D.

2018-03-01

The development of reliable redox-based resistive random-access memory devices requires understanding and disentangling concurrent effects present at memristive interfaces. We report on the fabrication and electrical characterization of TiO x /La1/3Ca2/3MnO3-x microstructured interfaces and on the modeling of their memristive behavior. We show that a careful tuning of the applied external electrical stimuli allows controlling the redox process between both layers, obtaining multilevel non-volatile resistance states. We simulate the oxygen vacancies dynamics at the interface between both oxides, and successfully reproduce the experimental electrical behavior after the inclusion of an electronic effect, related to the presence of an n-p diode at the interface. The formation of the diode is due to the n- and p-character of TiO x and La1/3Ca2/3MnO3-x , respectively. Our analysis indicates that oxygen vacancies migration between both layers is triggered after the diode is polarized either in forward mode or in reverse mode above breakdown. Electrical measurements at different temperatures suggest that the diode can be characterized as Zener-type. The advantages of our junctions for their implementation in RRAM devices are finally discussed.

Enhanced ferroelectric polarization and magnetization in BiFe{sub 1−x}Sc{sub x}O{sub 3} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, C.A.; Pang, H.Z.; Zhang, A.H.

2015-10-15

Highlights: • Single phase Sc doped BFO ceramics were successfully fabricated. • Dielectric constant and magnetization are enhanced in doped BFO system. • Polarization first increases and then decreases in doped BFO system. • M{sub r} of 0.0105 emu/g and P{sub r} of 16.1 μC/cm{sup 2} were revealed simultaneously at x = 0.01. - Abstract: Multiferroic BiFe{sub 1−x}Sc{sub x}O{sub 3} ceramics with x = 0.00–0.10 were synthesized by rapid liquid phase sintering. The influences of Sc doping on the crystalline structures, dielectric, ferroelectric, and magnetic behaviors of BiFeO{sub 3} ceramics were explored. The X-ray diffraction and the Raman spectrometric analysismore » revealed that all the samples are nearly single phase of rhombohedral structure with the incorporation of Sc ions into BiFeO{sub 3}. With increase doping concentration of x, the dielectric constant, dielectric loss, and remnant polarization for the doped BiFeO{sub 3} increase first and then drop down with further rise of x. A saturated ferroelectric polarization can be achieved at a small amount of Sc doping concentration (x < 0.03), with a optimized remnant polarization of 17.6 μC/cm{sup 2} at x = 0.03. Meanwhile, the magnetization is also slightly increased by introducing Sc dopant, with a maximum remnant magnetization of 0.0105 emu/g at x = 0.01. These results indicate that BiFeO{sub 3} ceramics with small amounts of Sc-doping may be promising for applications in magnetoelectric devices.« less

Local surrounding of Mn in LaMn 1-xCo xO 3 compounds by means of EXAFS on Mn-K

NASA Astrophysics Data System (ADS)

Procházka, Vít; Sikora, Marcin; Kapusta, Czeslaw; Štěpánková, Helena; Chlan, Vojtěch; Knížek, Karel; Jirák, Zdeněk

2010-05-01

A systematic study of LaMn 1-xCo xO 3 perovskite series by means of X-ray absorption spectroscopy in the extended X-ray absorption fine structure (EXAFS) range of the K-absorption edge of Mn is reported. The Mn-K edge absorption measurements in the EXAFS region were performed to study the local surrounding of Mn ions. Polycrystalline powder samples of LaMn 1-xCo xO 3 ( x=0, 0.02; 0.2; 0.4; 0.5; 0.6; 0.8) prepared by solid-state reaction were used. The EXAFS spectra were analyzed with the FEFF8 computer program. The Mn-O distances of Mn to the nearest oxygen surroundings were evaluated for the samples in the series and compared with the Co-O distances obtained by EXAFS in V. Procházka et al., JMMM 310 (2007) 197 and with results of X-ray powder diffraction in C. Autret, J. Phys. Condens. Matter 17 (2005) 1601.

Signature of magnetoelectric coupling of xNiFe2O4 - (1-x)HoMnO3 (x = 0.1 and 0.3) multiferroic nanocomposites

NASA Astrophysics Data System (ADS)

Mandal, S. K.; Debnath, Rajesh; Singh, Swati; Nath, A.; Dey, P.; Nath, T. K.

2017-12-01

The magnetoelectric coupling of xNiFe2O4-(1-x)HoMnO3 (x = 0.1 and 0.3) multiferroics nanocomposites prepared through low temperature chemical pyrophoric reaction process has been investigated at room temperature. The signature of magnetoelectric coefficient of these nanocomposites is mainly due to the magnetostriction and magnetodielectric properties of the materials. These nanocomposites show the ferroelectric behaviour at room temperature. AC electrical properties of nanocomposites have been studied with applied magnetic fields and temperatures. Nyquist plots at different magnetic fields and temperatures have been fitted using parallel combinations of resistance-capacitor circuits. Moreover, we have estimated activation energy of those composites using Arrhenius relation, which indicates that same kinds of charge carrier are responsible for relaxation process in grain boundaries and grain of the sample. Furthermore, from the analysis of ac conductivity data as a function of frequency is attributed to the large polaronic hopping in the conduction process in the system.

Optoelectronic Properties of X-Doped (X = O, S, Te) Photovoltaic CSe with Puckered Structure.

PubMed

Zhang, Qiang; Xin, Tianyuan; Lu, Xiaoke; Wang, Yuexia

2018-03-16

We exploited novel two-dimensional (2D) carbon selenide (CSe) with a structure analogous to phosphorene, and probed its electronics and optoelectronics. Calculating phonon spectra using the density functional perturbation theory (DFPT) method indicated that 2D CSe possesses dynamic stability, which made it possible to tune and equip CSe with outstanding properties by way of X-doping (X = O, S, Te), i.e., X substituting Se atoms. Then systematic investigation on the structural, electronic, and optical properties of pristine and X-doped monolayer CSe was carried out using the density functional theory (DFT) method. It was found that the bonding feature of C-X is intimately associated with the electronegativity and radius of the doping atoms, which leads to diverse electronic and optical properties for doping different group VI elements. All the systems possess direct gaps, except for O-doping. Substituting O for Se atoms in monolayer CSe brings about a transition from a direct Γ-Γ band gap to an indirect Γ-Y band gap. Moreover, the value of the band gap decreases with increased doping concentration and radius of doping atoms. A red shift in absorption spectra occurs toward the visible range of radiation after doping, and the red-shift phenomenon becomes more obvious with increased radius and concentration of doping atoms. The results can be useful for filtering doping atoms according to their radius or electronegativity in order to tailor optical spectra efficiently.

Optoelectronic Properties of X-Doped (X = O, S, Te) Photovoltaic CSe with Puckered Structure

PubMed Central

Zhang, Qiang; Xin, Tianyuan; Lu, Xiaoke; Wang, Yuexia

2018-01-01

We exploited novel two-dimensional (2D) carbon selenide (CSe) with a structure analogous to phosphorene, and probed its electronics and optoelectronics. Calculating phonon spectra using the density functional perturbation theory (DFPT) method indicated that 2D CSe possesses dynamic stability, which made it possible to tune and equip CSe with outstanding properties by way of X-doping (X = O, S, Te), i.e., X substituting Se atoms. Then systematic investigation on the structural, electronic, and optical properties of pristine and X-doped monolayer CSe was carried out using the density functional theory (DFT) method. It was found that the bonding feature of C-X is intimately associated with the electronegativity and radius of the doping atoms, which leads to diverse electronic and optical properties for doping different group VI elements. All the systems possess direct gaps, except for O-doping. Substituting O for Se atoms in monolayer CSe brings about a transition from a direct Γ-Γ band gap to an indirect Γ-Y band gap. Moreover, the value of the band gap decreases with increased doping concentration and radius of doping atoms. A red shift in absorption spectra occurs toward the visible range of radiation after doping, and the red-shift phenomenon becomes more obvious with increased radius and concentration of doping atoms. The results can be useful for filtering doping atoms according to their radius or electronegativity in order to tailor optical spectra efficiently. PMID:29547504

Dielectric studies of (x) NiFe2O4 + (1 - x) BaTi0.9Zr0.1O3 (where x = 0, 0.25, 0.50, 0.75 and 1)

NASA Astrophysics Data System (ADS)

Wadhwani, Kiran; Srivastava, Subodh; Mathur, Shubhra

2018-05-01

We present the room temperature dielectric studies of the samples in the series (x) NiFe2O4 + (1-x) BaTi0.9Zr0.1O3 (where x = 0, 0.25, 0.50, 0.75 and 1) containing nickel ferrite and Zr substituted barium titanate as the ferroelectric phase and their magnetoelectric (ME) composites in mixed in different molar ratios. Solid state diffusion has been used for the synthesis of samples. Powder X-ray diffraction (XRD) confirms the formation of ferrite and ferroelectric phases and their presence in all three composites with no impurity traces. Room temperature dielectric measurements have been made as a function of frequency (ranging from 100 Hz to 1 MHz).

Layered-to-Rock-Salt Transformation in Desodiated Na xCrO 2 ( x 0.4)

DOE PAGES

Bo, Shou-Hang; Li, Xin; Toumar, Alexandra J.; ...

2016-02-01

O3 layered sodium transition metal oxides (i.e., NaMO 2, M = Ti, V, Cr, Mn, Fe, Co, Ni) are a promising class of cathode materials for Na-ion battery applications. These materials, however, all suffer from severe capacity decay when the extraction of Na exceeds certain capacity limits. Understanding the causes of this capacity decay is critical to unlocking the potential of these materials for battery applications. In this work, we investigate the structural origins of capacity decay for one of the compounds in this class, NaCrO 2. The (de)sodiation processes of NaCrO 2 were studied both in situ and exmore » situ through X-ray and electron diffraction measurements. We demonstrate that Na xCrO 2 (0 < x < 1) remains in the layered structural framework without Cr migration up to a composition of Na 0.4CrO 2. Further removal of Na beyond this composition triggers a layered-to-rock-salt transformation, which converts P'3-Na 0.4CrO 2 into the rock-salt CrO 2 phase. This structural transformation proceeds via the formation of an intermediate O3 Na δCrO 2 phase that contains Cr in both Na and Cr slabs and shares very similar lattice dimensions with those of rock-salt CrO 2. It is intriguing to note that intercalation of alkaline ions (i.e., Na + and Li + ) into the rock-salt CrO 2 and O3 Na δCrO 2 structures is actually possible, albeit in a limited amount (~0.2 per formula unit). When these results were analyzed under the context of electrochemistry data, it was apparent that preventing the layered-to-rock-salt transformation is crucial to improve the cyclability of NaCrO 2. Possible strategies for mitigating this detrimental phase transition are proposed.« less

Thermoelectric and Magnetic Properties of Sn1- x O2:Mn0.5 x Co0.5 x Nanoparticles Produced by the Microwave Technique

NASA Astrophysics Data System (ADS)

Salah, Numan; Habib, Sami; Azam, Ameer

2017-02-01

Nanoparticles (NPs) of Sn1- x O2:Mn0.5 x Co0.5 x with x = 0.02, 0.04, 0.06, 0.08 and 0.1 were synthesized by the microwave-assisted route and characterized for their thermoelectric and magnetic properties. As a result of Mn and Co co-doping, a considerable increase in the values of energy band gap and lattice constant c of Sn1- x O2:Mn0.5 x Co0.5 x NPs was observed. The x-ray photoelectron spectroscopy spectra revealed that Mn and Co ions were incorporated in their 4+ and 2+ states, respectively. The resistivity and calculated activation energy of these NPs were found to decrease by increasing the Mn and Co contents. A negative Seebeck coefficient was observed, whose value was found to be significantly increased by increasing the value of x. The magnetic measurement results revealed that all the microwave-synthesized Sn1- x O2:Mn0.5 x Co0.5 x NPs including the pure SnO2 have distinctly wide hysteresis loops. This indicates that samples have room-temperature ferromagnetism. The optimum value for x to have maximum saturation magnetism was observed to be 0.04. Diamagnetic contributions from the core of these NPs were noticed at higher magnetic fields. The observed magnetism was attributed to the presence of defects at the NPs' interfacing sites, grain boundaries, atom vacancies and an optimum level of Mn and Co co-dopants. The observed wide hysteresis loops in these NPs might be useful for producing nanoscale magnets and magnetic memory devices. Moreover, the observed thermoelectric properties, i.e. Seebeck coefficient and power factor in these NPs, might be useful for the development of thermoelectric devices.

Synthesis and characterization of lithium aluminum-doped spinel (LiAl xMn 2- xO 4) for lithium secondary battery

NASA Astrophysics Data System (ADS)

Lee, Yun-Sung; Kumada, Naoki; Yoshio, Masaki

LiAl xMn 2- xO 4 has been synthesized using various aluminum starting materials, such as Al(NO 3) 3, Al(OH) 3, AlF 3 and Al 2O 3 at 600-800°C for 20 h in air or oxygen atmosphere. A melt-impregnation method was used to synthesize Al-doped spinel with good battery performance in this research. The Al-doped content and the intensity ratio of (3 1 1)/(4 0 0) peaks can be important parameters in synthesizing Al-doped spinel which satisfies the requirements of high discharge capacity and good cycleability at the same time. The decrease in Mn 3+ ion by Al substitution induces a high average oxidation state of Mn ion in the LiAl xMn 2- xO 4 material. The electrochemical behavior of all samples was studied in Li/LiPF 6-EC/DMC (1:2 by volume)/LiAl xMn 2- xO 4 cells. Especially, the initial and last discharge capacity of LiAl 0.09Mn 1.97O 4 using LiOH, Mn 3O 4 and Al(OH) 3 complex were 128.7 and 115.5 mAh/g after 100 cycles. The Al substitution in LiMn 2O 4 was an excellent method of enhancing the cycleability of stoichiometric spinel during electrochemical cycling.

Experimental and theoretical comparison of the O K-edge nonresonant inelastic X-ray scattering and X-ray absorption spectra of NaReO4.

PubMed

Bradley, Joseph A; Yang, Ping; Batista, Enrique R; Boland, Kevin S; Burns, Carol J; Clark, David L; Conradson, Steven D; Kozimor, Stosh A; Martin, Richard L; Seidler, Gerald T; Scott, Brian L; Shuh, David K; Tyliszczak, Tolek; Wilkerson, Marianne P; Wolfsberg, Laura E

2010-10-06

Accurate X-ray absorption spectra (XAS) of first row atoms, e.g., O, are notoriously difficult to obtain due to the extreme sensitivity of the measurement to surface contamination, self-absorption, and saturation affects. Herein, we describe a comprehensive approach for determining reliable O K-edge XAS data for ReO(4)(1-) and provide methodology for obtaining trustworthy and quantitative data on nonconducting molecular systems, even in the presence of surface contamination. This involves comparing spectra measured by nonresonant inelastic X-ray scattering (NRIXS), a bulk-sensitive technique that is not prone to X-ray self-absorption and provides exact peak intensities, with XAS spectra obtained by three different detection modes, namely total electron yield (TEY), fluorescence yield (FY), and scanning transmission X-ray microscopy (STXM). For ReO(4)(1-), TEY measurements were heavily influenced by surface contamination, while the FY and STXM data agree well with the bulk NRIXS analysis. These spectra all showed two intense pre-edge features indicative of the covalent interaction between the Re 5d and O 2p orbitals. Density functional theory calculations were used to assign these two peaks as O 1s excitations to the e and t(2) molecular orbitals that result from Re 5d and O 2p covalent mixing in T(d) symmetry. Electronic structure calculations were used to determine the amount of O 2p character (%) in these molecular orbitals. Time dependent-density functional theory (TD-DFT) was also used to calculate the energies and intensities of the pre-edge transitions. Overall, under these experimental conditions, this analysis suggests that NRIXS, STXM, and FY operate cooperatively, providing a sound basis for validation of bulk-like excitation spectra and, in combination with electronic structure calculations, suggest that NaReO(4) may serve as a well-defined O K-edge energy and intensity standard for future O K-edge XAS studies.

Structural morphology of YBa 2Cu 3O 7- x

NASA Astrophysics Data System (ADS)

Sun, B. N.; Hartman, P.; Woensdregt, C. F.; Schmid, H.

1990-03-01

The structural morphology of YBa 2Cu 3O 7- x (YBCO) has been investigated by application of the periodic bond chain (PBC) theory. For x=1, the F forms were found to be {001}, {011}, {013}, {112} and {114}. Attachment energies have been calculated in broken bond model and in an electrostatic point charge model. For x=1 the theoretical growth habit is tabular to platy {001} with {011} as side faces. For x=0 {010} also becomes an F form. The habit is isometric with large {001} and {011} and small {010} faces. The outermost layer of {001} contains half of the Cu + ( x=1) or Cu 3+ and O 2- ( x=0) ions in an ordered arrangement based on a c(2x2) quadratic lattice. For the outermost layer of (010) ( x=0) an ordering scheme of the copper and oxygen ions is proposed. The occurrence of {010} rather than {011} on grown crystals has to be ascribed to external factors.

Study on the solid solution of YMn{sub 1-x}Fe{sub x}O{sub 3}: Structural, magnetic and dielectric properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samal, S.L.; Green, W.; Lofland, S.E.

The solid solution of YMn{sub 1-x}Fe{sub x}O{sub 3} (x=0.0, 0.1, 0.2, 0.3, 0.5, 1.0) was synthesized from the citrate precursor route. The hexagonal crystal structure related to YMnO{sub 3} was stable for x{<=}0.3. Rietveld refinement was carried out on the composition for x=0.3 and was refined to a major hexagonal phase ({approx}97%) with 3% of orthorhombic Y(Fe/Mn)O{sub 3} phase. The a-axis lattice constant increases and the c-axis lattice constant decreases with x for x{<=}0.2. The increase in the c-axis lattice constant at x=0.3 could be due to the doping of significant amount of d{sup 5} ion (high spin Fe{sup 3+}more » ion) in a trigonal bipyramidal crystal field. The detailed structural, magnetic and dielectric properties are discussed. - Graphical abstract: Temperature dependence of {epsilon} of YMn{sub 1-x}Fe{sub x}O{sub 3} (0.0{<=}x{<=}0.3) at 100 kHz. Inset shows the temperature variation of inverse magnetic susceptibility.« less

YBa2Cu3O x superconducting nanorods

NASA Astrophysics Data System (ADS)

Rieken, William; Bhargava, Atit; Horie, Rie; Akimitsu, Jun; Daimon, Hiroshi

2018-02-01

Herein, we report the synthesis of YBa2Cu3O x superconducting nanorods performed by solution chemistry. Initially, a mixture of fine-grained coprecipitated powder was obtained and subsequently converted to YBa2Cu3O x nanorods by heating to 1223 K in oxygen for 12 h. The nanorods are superconducting without the need for any further sintering or oxygenation, thereby providing an avenue for direct application to substrates at room temperature or direct use as formed nanorods. A critical superconducting transition temperature T c of about 92 K was achieved at a critical magnetic field of 10 Oe.

The A2Πi˜X2Σ+ interaction in CO +: Deperturbation analyses of B- A and A- X bands of 12C 16O +, 13C 16O + and 14C 16O +

NASA Astrophysics Data System (ADS)

Coxon, John A.; Kępa, Ryszard; Piotrowska, Izabela

2010-08-01

The 1-0, 6-0 and 6-1 bands of the A2Πi→X2Σ+ system of 13C 16O + and the 2-0 and 2-1 bands of the A2Πi→X2Σ+ system of 14C 16O + have been recorded at high resolution for the first time. The 0-2 and 5-0 bands of the A → X system of 12C 16O + have also been recorded at higher resolution than in previous work. The spectra were excited in an air-cooled hollow cathode discharge and photographed using a 2-m plane grating spectrograph. The spectral resolution and the Doppler-broadened line widths are both ˜0.12 cm -1, and the experimental measurement precision of resolved lines is ˜0.02 cm -1. The measured line positions, sometimes in combination with literature data on the B2Σ+→A2Πi transition, have been employed in deperturbation analyses of level crossings in the near-degenerate A(0)˜ X(10) and A(5)˜ X(14) interactions in 12C 16O +, the A(1)˜ X(11) and A(6)˜ X(15) interactions in 13C 16O +, and the A(2)˜ X(12) interaction in 14C 16O +. No radial dependence of the electronic perturbation matrix elements HSO( r) and HRE( r) could be detected over the narrow range of r-centroids (1.477-1.501 Å), and the mean values of these parameters are HSO = -49.06(15) cm -1 and HRE = 0.211(2). Using iteratively improved RKR potentials and FC-overlap integrals, the mean HSO and HRE were employed in least-squares analyses of A → X literature data involving A( υ) levels of the three isotopologues that are affected by interactions with one or two distant X( υ∗) levels. The fitted parameters of the A2Πi state ( B υ, A υ, A Dυ, p υ, q υ) exhibit υ-dependences that are much smoother than those employing perturbed parameters determined in previous investigations. In addition, a significant electronic isotope effect has been characterized. The separations Te( A)- Te( X) of the minima of the A and X states of 13C 16O + and 14C 16O + are less than that of 12C 16O + by 0.39 and 0.73 cm -1, respectively. Although Born-Oppenheimer breakdown of this magnitude is

Optical properties of La{sub 2}CuO{sub 4} and La{sub 2-x}Ca{sub x}CuO{sub 4} crystallites in UV-vis-NIR region synthesized by sol-gel process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Yifeng; Huang Jianfeng, E-mail: hjfnpu@163.com; Cao Liyun

2012-02-15

La{sub 2}CuO{sub 4} and La{sub 2-x}Ca{sub x}CuO{sub 4} crystallites were prepared via a simple sol-gel process. The as-prepared La{sub 2}CuO{sub 4} and La{sub 2} {sub -x}Ca{sub x}CuO{sub 4} crystallites were characterized by X-ray diffraction, transmission electron microscope and UV-vis-NIR spectra. Results show that the grain size of La{sub 2}CuO{sub 4} crystallites increases with the increase of heat treatment temperature from 600 Degree-Sign C to 800 Degree-Sign C. Optical properties show that La{sub 2}CuO{sub 4} crystallites have broad absorption both in the UV-vis region and in the NIR region. The band gap of the as-prepared crystallites decreases from 1.367 eV tomore » 1.284 eV with the increase of calcination temperature from 600 Degree-Sign C to 800 Degree-Sign C. In the series of La{sub 2-x}Ca{sub x}CuO{sub 4} compounds (x = 0.05, 0.08, 0.10, 0.12, 0.15 and 0.20), all of the samples exhibit an orthogonal crystal structure and the solubility limit of Ca{sup 2+} in La{sub 2}CuO{sub 4} is within the range of x = 0.12-0.15. In the whole UV-vis-NIR region, La{sub 2-x}Ca{sub x}CuO{sub 4} crystallites exhibit a broad absorption and the corresponding band gap first increases and then decreases with increasing of Ca{sup 2+} content. - Highlights: Black-Right-Pointing-Pointer The optical band gap can be tuned by adjusting the grain size and Ca{sup 2+} content. Black-Right-Pointing-Pointer La{sub 2}CuO{sub 4} crystallites exhibit a broad absorption band both in the UV-vis region and in the NIR region. Black-Right-Pointing-Pointer The band gap increases from 1.284 eV to 1.319 eV with the decrease of heat treatment temperature. Black-Right-Pointing-Pointer In the whole UV-vis-NIR region, the La{sub 2-x}Ca{sub x}CuO{sub 4} crystallites displayed a broad absorption. Black-Right-Pointing-Pointer The band gap of La{sub 2-x}Ca{sub x}CuO{sub 4} increases linearly with doping level when 0 {<=} x {<=} 0.12.« less

Surface compositions of atomic layer deposited Zn{sub 1−x}Mg{sub x}O thin films studied using Auger electron spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Ting; Romero, Danilo; Gomez, Romel D., E-mail: rdgomez@umd.edu

2015-09-15

In this paper, the authors present Auger electron spectroscopy (AES) studies of Zn{sub 1−x}Mg{sub x}O (ZMO) films grown via interrupted atomic-layer deposition (ALD) techniques. The ZMO films were fabricated by alternating ALD deposition of ZnO and MgO layers up to 1000 cycles. Zn{sub 1−x}Mg{sub x}O films with progressively decreasing Mg/Zn ratios (Mg/Zn = 1/1, 1/2, 1/3, 1/4, 1/5, 1/6, 1/9, and 2/8, 3/12, 4/16, and 5/20) were fabricated for this study. The AES results exhibit an abrupt drop of Mg composition on the ZMO surface when the Mg/Zn < 1/3. Additionally, the surface composition ratios of O to Mg, O to Zn, and Mgmore » to Zn were estimated with known Auger sensitivity factors. The results indicate that Mg ions diffuse into the bulk, forming Zn{sub 1−x}Mg{sub x}O alloys.« less

Rate Coefficient for Collisional Removal of O2(X3Σ ^-g, v = 1) with O Atoms at 240 K

NASA Astrophysics Data System (ADS)

Pejaković, D. A.; Campbell, Z.; Kalogerakis, K. S.; Copeland, R. A.; Slanger, T. G.

2004-12-01

Knowledge of the water concentration profile is key to understanding of the chemistry and energy flow in the stratosphere and mesosphere. One of the tasks of the SABER instrument in NASA's TIMED mission is to measure water vapor concentration by detecting H2O(ν 2) emission in the 6.8 μ m region. An important source of the H2O(ν 2) emission is the collisional deactivation of vibrationally excited O2: O2(X3Σ ^-g, v = 1) + H2O <-> O2(X3Σ ^-g, v = 0) + H2O(ν 2). For reliable interpretation of the SABER data it is crucial to determine rate coefficient for the competing process: O2(X3Σ ^-g, v = 1) + O(3P) -> O2(X3Σ ^-g, v = 0) + O(3P) [1]. Laboratory measurements are reported of the rate coefficient for collisional removal of O2(X3Σ ^-g, v = 1) by O(3P) at a temperature of 240 K, relevant to the upper mesosphere. Instead of directly detecting the O2(X3Σ ^-g, v = 1) population, a novel, technically simpler, approach is used in which the v = 1 level of the O2(a1Δ g) state is monitored. With ground-state O2 present, owing to the rapid equilibration of the O2(X3Σ ^-g, v = 1) and O2(a1Δ g, v = 1) populations via the processes O2(a1Δ g, v = 1) + O2(X3Σ ^-g, v = 0) <-> O2(a1Δ g, v = 0) + O2(X3Σ ^-g, v = 1), the information on the O2(X3Σ ^-g, v = 1) kinetics is extracted from the O2(a1Δ g, v = 1) temporal evolution. A two-laser method is employed, in which the pulsed output of the first laser near 285 nm photodissociates ozone to produce atomic oxygen and O2(a1Δ g, v = 1), and the pulsed output of the second laser detects O2(a1Δ g, v = 1) via the resonance-enhanced multiphoton ionization. In the same experiment, rate coefficients for removal of O2(a1Δ g, v = 1) with the atmospherically relevant colliders O2, CO2, and O also were measured at room temperature and 240 K. The measured rate coefficient for O2(X3Σ ^-g, v = 1) removal by O(3P) is in the range 2--3 × 10-12 cm3s-1 at 240 K, compared to the recently measured room temperature value of about 3 × 10

Influence of oxygen vacancies on the magnetic and electrical properties of La1-xSrxMnO3-x/2 manganites

NASA Astrophysics Data System (ADS)

Trukhanov, S. V.; Lobanovski, L. S.; Bushinsky, M. V.; Khomchenko, V. A.; Pushkarev, N. V.; Troyanchuk, I. O.; Maignan, A.; Flahaut, D.; Szymczak, H.; Szymczak, R.

2004-11-01

The crystal structure, magnetization and electrical transport depending on the temperature and magnetic field for the doped stoichiometric La_{1-x}^{3 + } Sr_x^{2 + } Mn_{1-x}^{3 + } Mn_x^{4 + } O_3^{2-} as well as anion-deficient La_{1-x}^{3 + } Sr_x^{2 + } Mn^{3 + }O_{3-x/2}^{2-} (0le x le 0.30) ortomanganite systems have been experimentally studied. It is established that the stochiometric samples in the region of the 0 le x le 0.125 are an O'-orthorhombic perovskites whereas in the 0.175 le x le 0.30 - a rhombohedric. For the anion-deficient system the symmetry type of the unit cell is similar to the stoichiometric one. As a doping level increases the samples in the ground state undergo a number of the magnetic transitions. It is assumed that the samples with the large amount of oxygen vacancies are a cluster spin glasses (0.175 < x le 0.30) and temperature of the magnetic moment freezing is 40 K. All the anion-deficient samples are semiconductors and show considerable magnetoresistance over a wide temperature range with a peak for the x = 0.175 only. Concentration dependences of the spontaneous magnetization and magnetic ordering temperature for the anion-deficient La_{1-x}^{3 + } Sr_x^{2 + } Mn^{3 + }O_{3-x/2}^{2-} system have been established by the magnetic measurements and compared with those for the stoichiometric La_{1-x}^{3 + } Sr_x^{2 + } Mn_{1-x}^{3 + } Mn_x^{4 + } O_3^{2-} one. The magnetic propeprties of the anion-deficient samples may be interpreted on the base of the superexchange interaction and phase separation (chemical disorder) models.

High resolution x-ray absorption and emission spectroscopy of Li x CoO2 single crystals as a function delithiation

NASA Astrophysics Data System (ADS)

Simonelli, L.; Paris, E.; Iwai, C.; Miyoshi, K.; Takeuchi, J.; Mizokawa, T.; Saini, N. L.

2017-03-01

The effect of delithiation in Li x CoO2 is studied by high resolution Co K-edge x-ray absorption and x-ray emission spectroscopy. Polarization dependence of the x-ray absorption spectra on single crystal samples is exploited to reveal information on the anisotropic electronic structure. We find that the electronic structure of Li x CoO2 is significantly affected by delithiation in which the Co ions oxidation state tending to change from 3+  to 4+. The Co intersite (intrasite) 4p-3d hybridization suffers a decrease (increase) by delithiation. The unoccupied 3d t 2g orbitals with a 1g symmetry, containing substantial O 2p character, hybridize isotropically with Co 4p orbitals and likely to have itinerant character unlike anisotropically hybridized 3d e g orbitals. Such a peculiar electronic structure could have significant effect on the mobility of Li in Li x CoO2 cathode and hence the battery characteristics.

Cross-Dehydrogenative Coupling Reactions Between P(O)-H and X-H (X = S, N, O, P) Bonds.

PubMed

Hosseinian, Akram; Farshbaf, Sepideh; Fekri, Leila Zare; Nikpassand, Mohammad; Vessally, Esmail

2018-05-26

P(O)-X (X = S, N, O, P) bond-containing compounds have extensive application in medicinal chemistry, agrochemistry, and material chemistry. These useful organophosphorus compounds also have many applications in organic synthesis. In light of the importance of titled compounds, there is continuing interest in the development of synthetic methods for P(O)-X bonds construction. In the last 4 years, the direct coupling reaction of P(O)-H compounds with thiols, alcohols, and amines/amides has received much attention because of the atom-economic character. This review aims to give an overview of new developments in cross-dehydrogenative coupling reactions between P(O)-H and X-H (X = S, N, O, P) bonds, with special emphasis on the mechanistic aspects of the reactions.

Structural characteristics of Mg-doped (1-x)(K0.5Na0.5)NbO3-xLiSbO3 lead-free ceramics as revealed by Raman spectroscopy

NASA Astrophysics Data System (ADS)

Zhu, W. L.; Zhu, J. L.; Meng, Y.; Wang, M. S.; Zhu, B.; Zhu, X. H.; Zhu, J. G.; Xiao, D. Q.; Pezzotti, G.

2011-12-01

This paper presents a Raman spectroscopic study of compositional-change-induced structure variation and of the related mechanism of Mg doping in LiSbO3 (LS)-modified (K0.5Na0.5)NbO3 (KNN) ceramics. With increasing LS content from 0 to 0.06, a discontinuous shift towards higher wavenumbers was found for the band position of the A1g(v1) stretching mode of KNN, accompanied by a clearly nonlinear broadening of this band and a decrease in its intensity. Such morphological changes in the Raman spectrum result from two factors: (i) changes in polarizability/binding strength of the O-Nb-O vibration upon incorporation of Li ions in the KNN perovskitic structure and (ii) a polymorphic phase transition (PPT) from orthorhombic to tetragonal (O → T) phase at x > 0.04. Upon increasing the amount, w, of Mg dopant incorporated into the (1-x)KNN-xLS ceramic structure, the intensity of the Raman bands are enhanced, while the peak position and the full width at half maximum of the A1g(v1) mode was found to experience a clear dependence on both w and x. Raman characterization revealed that the mechanism of Mg doping is strongly correlated with the concentration of Li in the perovskite structure: Mg2+ ions will preferentially replace Li+ ions for low Mg doping while replace K/Na ions for higher doping of Mg. The PPT O → T was also found to be altered by the introduction of Mg and the critical value of LS concentration, xO-T, for incipient O → T transition in the KNN-xLS-wMT system was strongly dependent on Mg content, with xO → T being roughly equal to 0.04 + 2w, for the case of dilute Mg alloying.

Colloidal ZnO and Zn(1-x)Co(x)O tetrapod nanocrystals with tunable arm lengths.

PubMed

Hodges, James M; Fenton, Julie L; Gray, Jennifer L; Schaak, Raymond E

2015-10-28

Tetrapod-shaped ZnO nanocrystals exhibit exceptional optoelectronic properties, including intense ultraviolet photoluminescence emission, that make them attractive for applications that include lasers, sensors, and photocatalysts. However, synthetic methods that produce ZnO tetrapods typically include high-temperature vapor-deposition approaches that do not readily achieve characteristic dimensions of less than 100 nm or colloidal methods that require added metal dopants, which modify the inherent properties of ZnO. Here, we report a robust, modified solution-phase synthetic protocol for generating colloidal ZnO tetrapods that does not require the use of metal dopants. The ZnO tetrapod arm lengths can be tuned from 10 to 25 nm by adjusting the amount of Zn reagent used in the reaction. Subsequent seeded-growth produced even larger colloidal ZnO tetrapods with 62 nm arms. Photoluminescence (PL) measurements confirm that the tetrapods are of high crystalline quality, and the ultraviolet PL emission wavelengths that are observed fall between those of previously reported metal-doped colloidal ZnO tetrapods, which exhibit dopant-induced red- or blue-shifts. Furthermore, the reaction strategy can be modified to produce cobalt-substituted ZnO, offering a chemical pathway to tetrapod-shaped Zn1-xCoxO nanocrystals.

Ferroelastic domain structure and phase transition in single-crystalline [PbZn 1/3Nb 2/3O 3] 1-x[PbTiO 3] x observed via in situ x-ray microbeam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Tao; Du, Zehui; Tamura, Nobumichi

(1-x)Pb(Zn 1/3Nb 2/3)O 3-xPbTiO 3 ((1-x)PZN-xPT in short) is one of the most important piezoelectric materials. In this study, we extensively investigated (1-x)PZN-xPT (x = 0.07–0.11) ferroelectric single crystals using in-situ synchrotron μXRD, complemented by TEM and PFM, to correlate microstructures with phase transitions. The results reveal that (i) at 25°C, the equilibrium state of (1-x)PZN-xPT is a metastable orthorhombic phase for x = 0.07 and 0.08, while it shows coexistence of orthorhombic and tetragonal phases for x = 0.09 and x = 0.11, with all ferroelectric phases accompanied by ferroelastic domains; (ii) upon heating, the phase transformation in xmore » = 0.07 is Orthorhombic → Monoclinic → Tetragonal → Cubic. The coexistence of ferroelectric tetragonal and paraelectric cubic phases was in-situ observed in x = 0.08 above Curie temperature (T C), and (iii) phase transition can be explained by the evolution of the ferroelectric and ferroelastic domains. These results disclose that (1-x)PZN-xPT are in an unstable regime, which is possible factor for its anomalous dielectric response and high piezoelectric coefficient.« less

Ferroelastic domain structure and phase transition in single-crystalline [PbZn 1/3Nb 2/3O 3] 1-x[PbTiO 3] x observed via in situ x-ray microbeam

DOE PAGES

Li, Tao; Du, Zehui; Tamura, Nobumichi; ...

2017-11-10

(1-x)Pb(Zn 1/3Nb 2/3)O 3-xPbTiO 3 ((1-x)PZN-xPT in short) is one of the most important piezoelectric materials. In this study, we extensively investigated (1-x)PZN-xPT (x = 0.07–0.11) ferroelectric single crystals using in-situ synchrotron μXRD, complemented by TEM and PFM, to correlate microstructures with phase transitions. The results reveal that (i) at 25°C, the equilibrium state of (1-x)PZN-xPT is a metastable orthorhombic phase for x = 0.07 and 0.08, while it shows coexistence of orthorhombic and tetragonal phases for x = 0.09 and x = 0.11, with all ferroelectric phases accompanied by ferroelastic domains; (ii) upon heating, the phase transformation in xmore » = 0.07 is Orthorhombic → Monoclinic → Tetragonal → Cubic. The coexistence of ferroelectric tetragonal and paraelectric cubic phases was in-situ observed in x = 0.08 above Curie temperature (T C), and (iii) phase transition can be explained by the evolution of the ferroelectric and ferroelastic domains. These results disclose that (1-x)PZN-xPT are in an unstable regime, which is possible factor for its anomalous dielectric response and high piezoelectric coefficient.« less

Multistage ordering and critical singularities in C o1 -xZ nxA l2O4(0 ≤x ≤1 ) : Dilution and pressure effects in a magnetically frustrated system

NASA Astrophysics Data System (ADS)

Naka, Takashi; Sato, Koichi; Matsushita, Yoshitaka; Terada, Noriki; Ishii, Satoshi; Nakane, Takayuki; Taguchi, Minori; Nakayama, Minako; Hashishin, Takeshi; Ohara, Satoshi; Takami, Seiichi; Matsushita, Akiyuki

2015-06-01

We report comprehensive studies of the crystallographic, magnetic, and thermal properties of a spinel-type magnetically frustrated compound, CoA l2O4 , and a magnetically diluted system, C o1- xZ nxA l2O4 . These studies revealed the effects of dilution and disorder when the tetrahedral magnetic Co ion was replaced by the nonmagnetic Zn ion. Low-temperature anomalies were observed in magnetic susceptibility at x <0.6 . A multicritical point was apparent at T =3.4 K and x =0.12 , where the antiferromagnetic, spin-glass-like, and paramagnetic phases met. At that point, the quenched ferromagnetic component induced by a magnetic field during cooling was sharply enhanced and was observable below x =0.6 . At x ˜0.6 , magnetic susceptibility and specific heat were described by temperature power laws, χ ˜C /T ˜T-δ , in accord with the site percolation threshold of the diamond lattice. This behavior is reminiscent of a quantum critical singularity. We propose an x -temperature phase diagram in the range 0 ≤x ≤1 for C o1- xZ nxA l2O4 . The transition temperature of CoA l2O4 determined from magnetic susceptibility measured under hydrostatic pressure increased with increasing pressure.

Charge distribution and local structure and speciation in the UO 2+x and PuO 2+x binary oxides for x⩽0.25

NASA Astrophysics Data System (ADS)

Conradson, Steven D.; Begg, Bruce D.; Clark, David L.; den Auwer, Christophe; Ding, Mei; Dorhout, Peter K.; Espinosa-Faller, Francisco J.; Gordon, Pamela L.; Haire, Richard G.; Hess, Nancy J.; Hess, Ryan F.; Webster Keogh, D.; Lander, Gerard H.; Manara, Dario; Morales, Luis A.; Neu, Mary P.; Paviet-Hartmann, Patricia; Rebizant, Jean; Rondinella, Vincenzo V.; Runde, Wolfgang; Drew Tait, C.; Kirk Veirs, D.; Villella, Phillip M.; Wastin, Franck

2005-02-01

The local structure and chemical speciation of the mixed valence, fluorite-based oxides UO 2+x (0.00⩽ x⩽0.20) and PuO 2+x/PuO 2+x-y(OH) 2y· zH 2O have been determined by U/Pu L III XAFS spectroscopy. The U spectra indicate (1) that the O atoms are incorporated as oxo groups at short (1.75 Å) U-O distances consistent with U(VI) concomitant with a large range of U displacements that reduce the apparent number of U neighbors and (2) that the UO 2 fraction remains intact implying that these O defects interact to form clusters and give the heterogeneous structure consistent with the diffraction patterns. The PuO 2+x system, which does not show a separate phase at its x=0.25 endpoint, also displays (1) oxo groups at longer 1.9 Å distances consistent with Pu(V+ δ), (2) a multisite Pu-O distribution even when x is close to zero indicative of the formation of stable species with H 2O and its hydrolysis products with O 2-, and (3) a highly disordered, spectroscopically invisible Pu-Pu component. The structure and bonding in AnO 2+x are therefore more complicated than have previously been assumed and show both similarities but also distinct differences among the different elements.

Structural, magneto-optical properties and cation distribution of SrBi{sub x}La{sub x}Y{sub x}Fe{sub 12−3x}O{sub 19} (0.0 ≤ x ≤ 0.33) hexaferrites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Auwal, I.A.; Güngüneş, H.; Güner, S.

Highlights: • SrBi{sub x}La{sub x}Y{sub x}Fe{sub 12−3x}O{sub 19} (0.0 ≤ x ≤ 0.33) hexaferrites have been prepared by sol-gel autocombustion. • XRD patterns show that SrBi{sub x}La{sub x}Y{sub x}Fe{sub 12−3x}O{sub 19} (0.0 ≤ x ≤ 0.33) hexaferrites exhibit hexagonal structure. • The intrinsic coercivity (H{sub ci}) above 15000 Oe reveals that all samples are magnetically hard materials. - Abstract: SrBi{sub x}La{sub x}Y{sub x}Fe{sub 12−3x}O{sub 19} (0.0 ≤ x ≤ 0.33) hexaferrites were produced via sol-gel auto combustion. XRD patterns show that all the samples are single-phase M-type strontium hexaferrite (SrM). The magnetic hysteresis (σ-H) loops revealed the ferromagnetic nature ofmore » nanoparticles (NPs). The coercive field decreases from 4740 Oe to 2720 Oe with increasing ion content. In particular, SrBi{sub x}La{sub x}Y{sub x}Fe{sub 12−3x}O{sub 19} NPs with x = 0.0, 0.1, 0.2 have suitable magnetic characteristics (σ{sub s} = 62.03–64.72 emu/g and H{sub c} = 3105–4740 Oe) for magnetic recording. The intrinsic coercivity (H{sub ci}) above 15000 Oe reveals that all samples are magnetically hard materials. Tauc plots were used to specify the direct optical energy band gap (E{sub g}) of NPs. The E{sub g} values are between 1.76 eV and 1.85 eV. {sup 57}Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting, relative area and hyperfine magnetic field values on Bi{sup 3+} La{sup 3+} and Y{sup 3+} substitutions have been determined.« less

Structural and electronic properties of Sr{sub x}Ba{sub 1-x}SnO{sub 3} from first principles calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moreira, E.; Henriques, J.M.; Azevedo, D.L.

2012-03-15

Neutron diffraction data for Sr{sub x}Ba{sub 1-x}SnO{sub 3} (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) solid solutions were used as inputs to obtain optimized geometries and electronic properties using the density functional theory (DFT) formalism considering both the local density and generalized gradient approximations, LDA and GGA, respectively. The crystal structures and SnO{sub 6} octahedra tilting angles found after total energy minimization agree well with experiment, specially for the GGA data. Elastic constants were also obtained and compared with theoretical and experimental results for cubic BaSnO{sub 3}. While the alloys with cubic unit cell have an indirect band gap, tetragonalmore » and orthorhombic alloys exhibit direct band gaps (exception made to x=1.0). The Kohn-Sham minimum electronic band gap oscillates from 1.52 eV (cubic x=0.0, LDA) to 2.61 eV (orthorhombic x=1.0, LDA), and from 0.74 eV (cubic BaSnO{sub 3}, GGA) to 1.97 eV (orthorhombic SrSnO{sub 3}, GGA). Parabolic interpolation of bands has allowed us to estimate the effective masses for charge carriers, which are shown to be anisotropic and larger for holes. - Graphical Abstract: Highlights: Black-Right-Pointing-Pointer DFT calculations were performed on Sr{sub x}Ba{sub 1-x}SnO{sub 3} solid solutions. Black-Right-Pointing-Pointer Calculated crystal structures agree well with experiment. Black-Right-Pointing-Pointer Alloys have direct or indirect gaps depending on the Sr molar fraction. Black-Right-Pointing-Pointer The Kohn-Sham gap variation from x=0.0 to x=1.0 is close to the experimental value. Black-Right-Pointing-Pointer Carrier effective masses are very anisotropic, specially for holes.« less

Curie-Weiss behavior of Y{sub 1-x}Sr{sub x}MnO{sub 3} (x = 0 and 0.03)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thakur, Rajesh K., E-mail: thakur.rajesh2009@gmail.com; Thakur, Rasna; Gaur, N. K.

2015-06-24

The effect of bivalent cation Sr-doping on magnetic properties in multiferroic YMnO{sub 3} manganites was systemically studied by DC magnetic measurements. Both of the reported samples were prepared by solid-state reaction method with composition Y{sub 1−x}Sr{sub x}MnO{sub 3} (x = 0.00 and 0.03). The X-ray diffraction (XRD) results show that the compounds are synthesized in hexagonal crystal structure with space group P6{sub 3}cm (JCPDS: 25-1079) and slight increase in the lattice parameter is observed with strontium doping. The magnetisation versus temperature curve shows no clear anomaly near the antiferromagnetic transition temperature (T{sub N}), however from the magnetic measurements at 1000Oemore » a slight increase in the magnetisation is clearly witnessed with increasing Stront ium content to the Y-site.« less

The structure and optical properties of Sr{sub 1−x}Ca{sub x}MoO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hopper, H.A.; Macphee, D.E.; Mclaughlin, A.C., E-mail: a.c.mclaughlin@abdn.ac.uk

2016-10-15

The solid solution Sr{sub 1−x}Ca{sub x}MoO{sub 3} (x=0.00, 0.05, 0.10, 0.13, 0.15 and 0.17) has successfully been synthesised and X-ray Powder diffraction has revealed the occurrence of structural phase transitions, from cubic Pm−3m to tetragonal I4/mcm, and then to orthorhombic Imma as the value of x increased. Discontinuities were observed in the cell parameters and bond lengths and angles at the transition from tetragonal to orthorhombic symmetry as a result of the switching of the octahedral rotation axis at the tetragonal to orthorhombic transition. The increased octahedral tilting could also be linked to the decrease in the band gap frommore » 2.20 eV to 2.10 eV as x increased from 0 to 0.17. - Graphical abstract: Table of Contents Figure Caption: Ultraviolet-visible absorbance spectra for Sr{sub 1−x}Ca{sub x}MoO{sub 3} showing a reduction in band gap upon increasing x as a result of increased octahedral tilting. - Highlights: • The solid solution Sr{sub 1−x}Ca{sub x}MoO{sub 3} has been synthesised. • Structural phase transitions are observed. • Discontinuities were observed in the cell parameters and bond lengths and angles. • Upon increasing x from 0 to 0.17 the band gap reduces from 2.20 eV to 2.10 eV.« less

Crystallographic and magnetic properties of sol-gel synthesized T xCo 1-xFe 2O 4 (T=Mn and Cr) thin films

NASA Astrophysics Data System (ADS)

Kim, Kwang Joo; Kyung Kim, Hee; Ran Park, Young; Choi, Seung-li; Eun Kim, Sung; Jung Lee, Hee; Yun Park, Jae; Jin Kim, Sam

Effects of Mn and Cr substitution for Co on crystallographic and magnetic properties of inverse-spinel CoFe 2O 4 thin films were investigated. The crystal structure of the samples remain cubic for x<1 with the lattice constant ( a0) increasing with x for Mn doping and remaining constant for Cr doping. Tetrahedral Fe 2+ ions were detected in Cr xCo 1-xFe 2O 4 by Mössbauer spectroscopy while no such ions existed in Mn xCo 1-xFe 2O 4. The appearance of the tetrahedral Fe 2+ ions can be explained in terms of the Cr 3+ substitution for the octahedral Co 2+ sites with the resultant charge imbalance being compensated by a reduction of the tetrahedral Fe 3+ into Fe 2+. The observed variation in a0 and magnetic properties can be partly explained in terms of Mn 2+ and Cr 3+ substitution of octahedral sites in Mn xCo 1-xFe 2O 4 and Cr xCo 1-xFe 2O 4, respectively.

Structure symmetry determination and magnetic evolution in Sr 2Ir 1–xRh xO 4

DOE PAGES

Ye, Feng; Wang, Xiaoping; Hoffmann, Christina; ...

2015-11-23

We use single-crystal neutron diffraction to determine the crystal structure symmetry and to study the magnetic evolution in the rhodium doped iridates Sr 2Ir 1–xRh xO 4 (0 ≤ x ≤ 0.16). Throughout this doping range, the crystal structure retains a tetragonal symmetry (space group I4 1/a) with two distinct magnetic Ir sites in the unit cell forming staggered IrO 6 rotation. Upon Rh doping, the magnetic order is suppressed and the magnetic moment of Ir4+ is reduced from 0.21 μ B/Ir for x = 0 to 0.18 μ B/Ir for x = 0.12. As a result, the magnetic structuremore » at x = 0.12 is different from that of the parent compound while the moments remain in the basal plane.« less

Transport and magnetic properties of disordered Li xV yO 2 ( x=0.8 and y=0.8)

NASA Astrophysics Data System (ADS)

Du, Fei; Li, Ang; Liu, Daliang; Zhan, Shiying; Hu, Fang; Wang, Chunzhong; Chen, Yan; Feng, Shouhua; Chen, Gang

2009-07-01

The magnetic and electron transport properties of rhombohedral Li xV yO 2 ( x=0.8 and y=0.8) are studied. The dc susceptibility of Li xV yO 2 can be well fitted to the modified Curie-Weiss law, which verified the paramagnetic ground state. The magnetic hysteresis and ac susceptibility also confirm this paramagnetism. The Li xV yO 2 exhibits semiconducting behavior, which is explained by thermal activated process at high temperature and variable-range hopping mechanism at low temperature. Anderson localization plays an important role in both the electron transport behavior and the magnetic behavior due to the site disorder between the Li + ion and V 4+ ion.

Relieving geometrical frustration through doping in the Dy1-x Ca x BaCo4O7 swedenborgites.

PubMed

Nath Panja, Soumendra; Kumar, Jitender; Dengre, Shanu; Nair, Sunil

2016-12-07

The geometrically frustrated antiferromagnet DyBaCo 4 O 7 is investigated through a combination of x-ray diffraction, magnetization and dielectric measurements. Systematic doping in the series Dy 1-x Ca x BaCo 4 O 7 causes a lifting of the geometrical frustration resulting in a structural transition from a trigonal P31c to an orthorhombic Pbn2 1 symmetry at x  =  0.4. This structural transition can also be accessed as a function of temperature, and all our orthorhombic specimens exhibit this transition at elevated temperatures. The temperature at which this structural transition occurs is observed to scale linearly with the mean ionic radius of the R site ion. However, CaBaCo 4 O 7 which has an equal number of Co 2+  and Co 3+ ions clearly violates this quasilinear relationship, indicating that charge ordering could also play a critical role in stabilizing the orthorhombic distortion in this system. Using thermoremanent magnetization measurements to circumvent the problem of the large paramagnetic background arising from Dy 3+ ions, we chart out the phase diagram of the Dy 1-x Ca x BaCo 4 O 7 series.

Characterization of magnetic and dielectric properties of Bi(1-x)Gd(x)FeO3 nanoparticles by local structure analyses.

PubMed

Yanoh, Takuya; Kurokawa, Akinobu; Takeuchi, Hiromasa; Yano, Shinya; Onuma, Kazuki; Kondo, Takaya; Miike, Kazunari; Miyasaka, Toshiki; Mibu, Ko; Ichiyanagi, Yuko

2014-03-01

Bi(1-x)Gd(x)FeO3 (0 < or = x < or = 1.0) nanoparticles were synthesized by a wet chemical method. The annealing temperatures were controlled to obtain single-phase Bi(1-x)Gd(x)FeO3 nanoparticles. The crystal diameters decreased as the number of doped Gd ions increased. The crystal structure changed, as the number of Gd ions increased, from rhombohedral to orthorhombic perovskite, at x = 0.2. The behavior of the magnetization curves observed at various values of x (x = 0.05, 0.1, 0.15) of the rhombohedral structure suggested that the canted antiferromagnetism and remanent magnetization (M(r)) drastically increased, compared with those at x = 0 (BiFeO3). It is suggested that the spin-canting angle of the Fe ions increased with the increase in the number of Gd ions. The dielectric properties at x = 0.1 showed that the dielectric loss (tan delta) was improved, compared with that at x = 0 (BiFeO3), by approximately 90%, while the real part of the dielectric constant epsilon' was reduced by approximately 15%. The reason is that the doping impurities restrained the reduction in the leakage current. It was found, from the X-ray absorption fine structure (XAFS) spectra, that Gd ions were doped accurately and that the symmetry of the B site was improved. The Mössbauer analysis suggested the existence of magnetic cycloid spiral ordering.

Estudo espectral em raios-X duros de fontes do tipo Z com o HEXTE/RXTE

NASA Astrophysics Data System (ADS)

D'Amico, F.; Heindl, W. A.; Rothschild, R. E.

2003-08-01

Apresentam-se os resultados de um estudo espectral em raios-X de fontes do tipo Z. As fontes do tipo Z são binárias de raios-X de baixa massa (BXBM) com campo magnético intermediário (B~109G). Esta classe de fontes é composta por apenas 6 fontes Galácticas (a saber: ScoX-1, 9, 7, CygX-2, 5 e 0). A nossa análise se concentra na faixa de raios-X duros (E ~ 20keV), até cerca de 200keV, faixa ótima de operação do telescópio "High Energy X-ray Timing Experiment" (HEXTE), um dos três telescópios de raios-X à bordo do Rossi X-ray Timing Explorer (RXTE). Nossa motivação para tal estudo, uma busca de caudas em raios-X duros em fontes do tipo Z, foi o pouco conhecimento sobre a emissão nesta faixa de energia das referidas fontes quando comparadas, por exemplo, as fontes do tipo atoll (também BXBM). Apresentam-se a análise/redução de dados e explicita-se a maneira como o HEXTE mede o ru1do de fundo. Especial atenção é direcionada a este item devido a localização das fontes do tipo Z e também ao problema de contaminação por fontes próximas. Com exceção de ScoX-1, nenhuma cauda em raios-X duros foi encontrada para as outras fontes, a despeito de resultados de detecção dessas caudas em algumas fontes pelo satélite BeppoSAX. As interpretações deste resultado serão apresentadas. Do ponto de vista deste estudo, nós deduzimos que a produção de caudas de raios-X duros em fontes do tipo Z é um processo disparado quando, pelo menos, uma condição é satisfeita: o brilho da componente térmica do espectro precisa estar acima de um certo valor limiar de ~4´1036ergs-1.

Preparation and characterization of epitaxial Fe{sub 2-x}Ti{sub x}O{sub 3} films with various Ti concentrations (0.5<x<1.0)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takada, Y.; Nakanishi, M.; Fujii, T.

2008-08-01

An ilmenite-hematite solid solution (Fe{sub 2-x}Ti{sub x}O{sub 3}) is one of the candidates for practical magnetic semiconductors with a high Curie temperature. We have prepared well-crystallized epitaxial Fe{sub 2-x}Ti{sub x}O{sub 3} films with a wide range of Ti concentrations--x=0.50, 0.60, 0.65, 0.76, 0.87, and 0.94--on {alpha}-Al{sub 2}O{sub 3}(001) substrates. The films are prepared by a reactive helicon plasma sputtering technique to evaporate Fe and TiO targets simultaneously under optimized oxygen pressure conditions. The structural characterizations of the films reveal that all films have a single phase of the ordered structure with R3 symmetry, where Ti-rich and Fe-rich layers are stackedmore » alternately along the c axis. All films have large ferrimagnetic moments at low temperature, and room temperature magnetization is clearly observed at x<0.7. The inverse temperature dependence of the resistivities of the films indicates their semiconducting behavior. The film resistivities decrease with decreasing Ti concentration.« less

Diffuse phase ferroelectric vs. Polomska transition in (1-x) BiFeO3-(x) Ba Zr0.025Ti0.975O3 (0.1 ≤ x ≤ 0.3) solid solutions

NASA Astrophysics Data System (ADS)

Jha, Pardeep K.; Jha, Priyanka A.; Singh, Vikash; Kumar, Pawan; Asokan, K.; Dwivedi, R. K.

2015-01-01

Investigations on the solid solutions (1-x) BiFeO3 - (x) Ba Zr0.025Ti0.975O3 (0.1 ≤ x ≤ 0.3) in the temperature range 300-750 K show colossal permittivity behavior and the occurrence of diffuse phase ferroelectric transition along with frequency dependent anomaly which disappears at temperature ˜450 K. For x = 0.3, these anomalies have been verified through differential scanning calorimetry and dielectric/impedance/conductivity measurements. The occurrence of peak in pyrocurrent (dPs/dT) vs. T plots also supports phase transition. With the increasing x, transition temperature decreases and diffusivity increases. This anomaly is absent at high frequencies (>100 kHz) in conductivity plots, indicating Polomska like surface phase transition, which is supported by modulus study.

Synchrotron X-ray diffraction study of the Ba{sub 1−x}SrSnO{sub 3} solid solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prodjosantoso, Anti K., E-mail: Prodjosantoso@yahoo.com; Zhou, Qingdi; Kennedy, Brendan J.

At room temperature the sequence of phases with increasing amounts of strontium in the stannate perovskite system Ba{sub 1−x}SrSnO{sub 3} has been established from high resolution synchrotron X-ray powder diffraction. The observed sequence orthorhombic (Pbnm), orthorhombic (Ibmm), tetragonal (I4/mcm), and cubic (Pm3-bar m) is a consequence of the sequential introduction of cooperative tilting of the corner sharing SnO{sub 6} octahedra. The cell volume changes smoothly across the series with no obvious discontinuities associated with the phase transitions. - Graphical abstract: Portions of the synchrotron X-ray diffraction profiles (λ=0.82453 Å) from selected Ba{sub 1−x}Sr{sub x}SnO{sub 3} samples together with the resultsmore » of fitting by the Rietveld method. Highlights: ► Structures of the stannate perovskites Ba{sub 1−x}SrSnO{sub 3} refined from synchrotron XRD. ► The sequence Pm3-bar m→I4/mcm→Ibmm→Pbnm results from tilting of the octahedra. ► The tilting maintains optimal bonding of the cations seen from the BVS analysis.« less

Substitution behavior of x(Na0.5K0.5)NbO3-(1 - x)BaTiO3 ceramics for multilayer ceramic capacitors by a near edge x-ray absorption fine structure analysis

NASA Astrophysics Data System (ADS)

Ha, Jooyeon; Ryu, Jiseung; Lee, Heesoo

2014-06-01

The doping effect of (Na0.5K0.5)NbO3 (NKN) as alternatives for rare-earth elements on the electrical properties of BaTiO3 has been investigated, in terms of their substitution behavior. The dielectric constant of a specimen with x = 0.05 was about 79% higher than that of pure BaTiO3, and the temperature coefficient of capacitance was satisfied by the X7R specification. The specimen with x = 0.05 showed the lowest tetragonality among the four compositions and had a fine grain size of <2 μm. Although the addition of NKN decreased the specimen's tetragonality, the electrical properties were enhanced by the formation of defect dipoles and conduction electrons, which resulted from an acceptor and donor substitution behavior. Through O K-edge near edge x-ray absorption fine structure spectroscopy, the practical substitution behavior was defined by the change in Ti 3d orbital states. The energy separation of the Ti 3d orbitals was more apparent with the specimen of x = 0.05, which is related to the donor level from the donor substitution of Nb5+ ion for Ti-sites. Therefore, the simultaneous substitution of Na+/K+ and Nb5+ ions into BaTiO3 can improve dielectric properties, based on the charge-transfer process.

Molecular Dynamics Simulation of the Structure and Ion Transport in the Ce1 - x Gd x O2 - δ|YSZ Heterosystem

NASA Astrophysics Data System (ADS)

Galin, M. Z.; Ivanov-Schitz, A. K.; Mazo, G. N.

2018-01-01

Molecular dynamics simulation has been used to develop a realistic atomistic model of two-layer Ce1 - x Gd x O2 - δ|YSZ heterosystem. It is shown that Ce1 - x Gd x O2 - δ and YSZ layers (about 15 and 16 Å thick, respectively) retain their crystal structure on the whole. The main structural distortions are found to occur near the Ce1 - x Gd x O2 - δ|YSZ geometric interface, within a narrow interfacial region of few angstroms thick. Both the generalized diffusion characteristics of the system as a whole and the oxygen diffusion coefficients in the layers are calculated, and the diffusion activation energies are determined.

Removal of urea from dilute streams using RVC/nano-NiO x -modified electrode.

PubMed

Tammam, Reham H; Touny, Ahmed H; Saleh, Mahmoud M

2018-05-08

Reticulated vitreous carbon (RVC), a high surface area electrode (40 cm 2 /cm 3 ), has been modified with nickel oxide nanoparticles (nano-NiO x ) and used for electrochemical oxidation of urea from alkaline solution. For the cyclic voltammetry measurements, the used dimensions are 0.8 cm × 0.8 cm × 0.3 cm. The purpose was to offer high specific surface area using a porous open network structure to accelerate the electrochemical conversion. NiO x nanoparticles have been synthesized via an electrochemical route at some experimental conditions. The morphological, structural, and electrochemical properties of the RVC/nano-NiO x are characterized by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and potentiostatic measurements. The fabricated electrode, RVC/nano-NiO x , demonstrates high electrocatalytic activity towards urea oxidation in an alkaline electrolyte. The onset potential of the RVC/nano-NiO x compared to that of the planar GC/NiO x is shifted to more negative value with higher specific activity. The different loadings of the NiO x have a substantial influence on the conversion of urea which has been evaluated from concentration-time curves. The urea concentration decreases with time to a limit dependent on the loading extent. Maximum conversion is obtained at 0.86 mg of NiO x per cm 3 of the RVC matrix.

Ge nanocrystals formed by furnace annealing of Ge(x)[SiO2](1-x) films: structure and optical properties

NASA Astrophysics Data System (ADS)

Volodin, V. A.; Cherkov, A. G.; Antonenko, A. Kh; Stoffel, M.; Rinnert, H.; Vergnat, M.

2017-07-01

Ge(x)[SiO2](1-x) (0.1  ⩽  x  ⩽  0.4) films were deposited onto Si(0 0 1) or fused quartz substrates using co-evaporation of both Ge and SiO2 in high vacuum. Germanium nanocrystals were synthesized in the SiO2 matrix by furnace annealing of Ge x [SiO2](1-x) films with x  ⩾  0.2. According to electron microscopy and Raman spectroscopy data, the average size of the nanocrystals depends weakly on the annealing temperature (700, 800, or 900 °C) and on the Ge concentration in the films. Neither amorphous Ge clusters nor Ge nanocrystals were observed in as-deposited and annealed Ge0.1[SiO2]0.9 films. Infrared absorption spectroscopy measurements show that the studied films do not contain a noticeable amount of GeO x clusters. After annealing at 900 °C intermixing of germanium and silicon atoms was still negligible thus preventing the formation of GeSi nanocrystals. For annealed samples, we report the observation of infrared photoluminescence at low temperatures, which can be explained by exciton recombination in Ge nanocrystals. Moreover, we report strong photoluminescence in the visible range at room temperature, which is certainly due to Ge-related defect-induced radiative transitions.

Structural and Magnetic Properties of Transition-Metal-Doped Zn 1-x Fe x O.

PubMed

Abdel-Baset, T A; Fang, Yue-Wen; Anis, B; Duan, Chun-Gang; Abdel-Hafiez, Mahmoud

2016-12-01

The ability to produce high-quality single-phase diluted magnetic semiconductors (DMS) is the driving factor to study DMS for spintronics applications. Fe-doped ZnO was synthesized by using a low-temperature co-precipitation technique producing Zn 1-x Fe x O nanoparticles (x= 0, 0.02, 0.04, 0.06, 0.08, and 0.1). Structural, Raman, density functional calculations, and magnetic studies have been carried out in studying the electronic structure and magnetic properties of Fe-doped ZnO. The results show that Fe atoms are substituted by Zn ions successfully. Due to the small ionic radius of Fe ions compared to that of a Zn ions, the crystal size decreases with an increasing dopant concentration. First-principle calculations indicate that the charge state of iron is Fe (2+) and Fe (3+) with a zinc vacancy or an interstitial oxygen anion, respectively. The calculations predict that the exchange interaction between transition metal ions can switch from the antiferromagnetic coupling into its quasi-degenerate ferromagnetic coupling by external perturbations. This is further supported and explains the observed ferromagnetic bahaviour at magnetic measurements. Magnetic measurements reveal that decreasing particle size increases the ferromagnetism volume fraction. Furthermore, introducing Fe into ZnO induces a strong magnetic moment without any distortion in the geometrical symmetry; it also reveals the ferromagnetic coupling.

Investigation of microstructural and electrical properties of composition dependent co-sputtered Hf1-x Ta x O2 thin films

NASA Astrophysics Data System (ADS)

Das, K. C.; Tripathy, N.; Ghosh, S. P.; Mohanta, S. K.; Nakamura, A.; Kar, J. P.

2017-11-01

Tantalum doped HfO2 gate dielectric thin films were deposited on silicon substrates using RF reactive co-sputtering by varying RF power of Ta target from 15 W to 90 W. The morphological, compositional and electrical properties of Hf1-x Ta x O2 films were systematically investigated. The Ta content was found to be increased up to 21% for a Ta target power of 90 W. The evolution of monoclinic phase of Hf1-x Ta x O2 was seen from XRD study upto RF power of 60 W and afterwards, the amorphous like behaviour is appeared. The featureless smooth surface with the decrease in granular morphology has been observed from FESEM micrographs of the doped films at higher RF powers of Ta. The flatband voltage is found to be shifted towards negative voltage in the capacitance-voltage plot, which was attributed to the enhancement in positive oxide charge density with rise in RF power. The interface charge density has a minimum value of 7.85  ×  1011 eV-1 cm-2 for the film deposited at Ta RF power of 75 W. The Hf1-x Ta x O2 films deposited at Ta target RF power of 90 W has shown lower leakage current. The high on/off ratio of the current during the set process in Hf1-x Ta x O2 based memristors is found suitable for bipolar resistive switching memory device applications.

NMR study of spin fluctuations and superconductivity in LaFeAsO1-xHx

NASA Astrophysics Data System (ADS)

Fujiwara, Naoki; Sakurai, Ryosuke; Iimura, Soushi; Matsuishi, Satoru; Hosono, Hideo; Yamakawa, Yoichi; Kontani, Hiroshi

2013-03-01

We have performed NMR measurements in LaFeAsO1-xHx, an isomorphic compound of LaFeAsO1-xFx. LaFeAsO1-xHx is most recently known for having double superconducting (SC) domes on H doping. LaFeAsO1-xHx is an electron- doped system, and protons act as H-1 as well as F-1. The first SC dome is very similar between F and H doping, suggesting that H doping supplies the same amount of electrons as F doping. Interestingly, an excess amount of H up to x=0.5 can be replaced with O2-. In the H-overdoped regime (x > 0 . 2), LaFeAsO1-xHx undergoes the second superconducting state. We measured the relaxation rate of LaFeAsO1-xHx for x=0.2 and 0.4, and fond an anomalous electronic state; spin fluctuations measured from 1 /T1 T is enhanced with increasing the doping level from x = 0 . 2 to 0.4. The enhancement of spin fluctuations with increasing carrier doping is a new phenomenon that has not observed in LaFeAsO1-xFx in which the upper limit of the doping level is at most x = 0 . 2 . We will discuss the phenomenon in relation to superconductivity. Grant (KAKENHI 23340101) from the Ministry of Education, Sports and Science, Japan

Memristor and selector devices fabricated from HfO2-xNx

NASA Astrophysics Data System (ADS)

Murdoch, B. J.; McCulloch, D. G.; Ganesan, R.; McKenzie, D. R.; Bilek, M. M. M.; Partridge, J. G.

2016-04-01

Monoclinic HfO2-xNx has been incorporated into two-terminal devices exhibiting either memristor or selector operation depending on the controlled inclusion/suppression of mobile oxygen vacancies. In HfO2 memristors containing oxygen vacancies, gradual conductance modulation, short-term plasticity, and long-term potentiation were observed using appropriate voltage-spike stimulation, suggesting suitability for artificial neural networks. Passivation of oxygen vacancies, confirmed by X-ray absorption spectroscopy, was achieved in HfO2-xNx films by the addition of nitrogen during growth. Selector devices formed on these films exhibited threshold switching and current controlled negative differential resistance consistent with thermally driven insulator to metal transitions.

Fabrication and electrochemical properties of activated CNF/Cu x Mn1- x Fe2O4 composite nanostructures

NASA Astrophysics Data System (ADS)

Nilmoung, Sukanya; Sonsupap, Somchai; Sawangphruk, Montree; Maensiri, Santi

2018-06-01

This work reports the fabrication and electrochemical properties of activated carbon nanofibers composited with copper manganese ferrite (ACNF/Cu x Mn1- x Fe2O4: x = 0.0, 0.2, 0.4, 0.6, 0.8) nanostructures. The obtained samples were characterized by means of X-ray diffraction, field emission scanning electron microscopy, Brunauer-Emmett-Teller analyzer, thermal gravimetric analysis, X-ray photoemission spectroscopy, and X-ray absorption spectroscopy. The supercapacitive behavior of the electrodes is tested using cyclic voltammetery, galvanostatic charge-discharge and electrochemical impedance spectroscopy. By varying ` x', the highest specific capacitance of 384 F/g at 2 mV/s using CV and 314 F/g at 2 A/g using GCD are obtained for the x = 0.2 electrode. The second one of 235 F/g at 2 mV/s using CV and 172 F/g at 2 A/g using GCD are observed for x = 0.8 electrode. The corresponding energy densities are 74 and 41 Wh/kg, respectively. It is observed that the cyclic stability of the prepared samples strongly depend on the amount of carbon, while the specific capacitance was enhanced by the sample with nearly proportional amount between carbon and CuMnFe2O4. Such results may arise from the synergetic effect between CuMnFe2O4 and ACNF.

Two superconducting transitions in single-crystal La 2 - x Ba x CuO 4

DOE PAGES

Tee, X. Y.; Ito, T.; Ushiyama, T.; ...

2017-02-27

Here, we use spatially-resolved transport techniques to investigate the superconducting properties of single crystals La 2-xBa xCuO 4. We also found a superconducting transition temperature T cs associated with the ab-plane surface region which is considerably higher than the bulk T c. This effect is pronounced in the region of charge carrier doping x with strong spin-charge stripe correlations, reaching T cs = 36 K or 1.64T c.

Magnetic properties of quadruple perovskite solid solutions Ca{sub 1–x}Y{sub x}Cu{sub 3}Fe{sub 4}O{sub 12} and Y{sub 1–y}Ce{sub x}Cu{sub 3}Fe{sub 4}O{sub 12}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murakami, Makoto; Mori, Shigeo; Yamada, Ikuya, E-mail: i-yamada@21c.osakafu-u.ac.jp

Magnetic properties of the quadruple perovskite solid solutions Ca{sub 1–x}Y{sub x}Cu{sub 3}Fe{sub 4}O{sub 12} and Y{sub 1–y}Ce{sub y}Cu{sub 3}Fe{sub 4}O{sub 12} are investigated. Ca{sub 1–x}Y{sub x}Cu{sub 3}Fe{sub 4}O{sub 12} shows continuous increase in the ferromagnetic transition temperature as x increases. Y{sub 1–y}Ce{sub y}Cu{sub 3}Fe{sub 4}O{sub 12} exhibits a ferromagnetic-antiferromagnetic transition in the vicinity of y = 0.5. These observations demonstrate the electron doping effect on magnetic properties of charge-disproportionated ACu{sub 3}Fe{sub 4}O{sub 12} phases.

Controlled synthesis of the antiperovskite oxide superconductor Sr3‑x SnO

NASA Astrophysics Data System (ADS)

Hausmann, J. N.; Oudah, M.; Ikeda, A.; Yonezawa, S.; Maeno, Y.

2018-05-01

A large variety of perovskite oxide superconductors are known, including some of the most prominent high-temperature and unconventional superconductors. However, superconductivity among the oxidation state inverted material class, the antiperovskite oxides, was recently reported for the first time. In this superconductor, Sr3‑x SnO, the unconventional ionic state Sn4‑ is realized and possible unconventional superconductivity due to a band inversion has been discussed. Here, we discuss an improved facile synthesis method, making it possible to control the strontium deficiency in Sr3‑x SnO. Additionally, a synthesis method above the melting point of Sr3SnO is presented. We show temperature dependence of magnetization and electrical resistivity for superconducting strontium deficient Sr3‑x SnO (T c ∼ 5 K) and for Sr3SnO without a superconducting transition in alternating current susceptibility down to 0.15 K. Further, we reveal a significant effect of strontium raw material purity on the superconductivity and achieve substantially increased M/M Meissner (∼1) compared to the highest value reported so far. More detailed characterizations utilizing powder x-ray diffraction and energy-dispersive x-ray spectroscopy show that a minor cubic phase, previously suggested to be another Sr3‑x SnO phase with a slightly larger lattice parameter, is SrO. The improved characterization and controlled synthesis reported herein enable detailed investigations on the superconducting nature and its dependency on the strontium deficiency in Sr3‑x SnO.

Local Matrix-Cluster Interactions In La1-x SrxCoO3.

NASA Astrophysics Data System (ADS)

Giblin, Sean; Terry, Ian; Boothroyd, Andrew; Prabhakaran, Dharmalingiam; Wu, Jing; Leighton, Chris

2006-03-01

Magneto-electronic phase separation plays an integral part in many recent advances in the understanding of correlated electron systems. We have studied the magnetically phase separated material La1-x SrxCoO3 and the parent compound LaCoO3, using muon spectroscopy and magnetic susceptibility measurements. The muon as a local magnetic probe is sensitive to the magnetic field distribution in LaCoO3 in the LS state, which is a direct consequence of magnetic excitons. We believe that these excitons are interacting with the Co ions undergoing the known thermally induced spin transition. By directly comparing the results of the parent compound with La1-x SrxCoO3 we can observe the hole-rich ferromagnetic clusters interacting with the neighboring hole poor matrix for low x. This mechanism, detected here for the first time, may play an important role in the rich electrical and magnetic properties of La1-x SrxCoO3.

Magnetic properties of (SrFe{sub 12}O{sub 19}){sub x}(CaCu{sub 3}Ti{sub 4}O{sub 12}){sub 1–x} composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eremina, R. M., E-mail: REremina@yandex.ru; Sharipov, K. R.; Yatsyk, I. V.

2016-07-15

New composite materials (SrFe{sub 12}O{sub 19}){sub x}(CaCu{sub 3}Ti{sub 4}O{sub 12}){sub 1–x} (x = 0, 0.05, 1) have been synthesized. Their magnetic properties are studied in the temperature range 5–300 K using the magnetic resonance and magnetometry methods. It is found that strontium hexaferrite microinclusions in the (SrFe{sub 12}O{sub 19}){sub 0.05}(CaCu{sub 3}Ti{sub 4}O{sub 12}){sub 0.95} composite “magnetize” CaCu{sub 3}Ti{sub 4}O{sub 12} at temperatures from 300 to 200 K, forming a ferrimagnetic particle near the SrFe{sub 12}O{sub 19} “core.” The magnetic resonance line below 200 K splits into two lines corresponding to SrFe{sub 12}O{sub 19} and CaCu{sub 3}Ti{sub 4}O{sub 12}. The coremore » effect decoration is manifested in the increase in the Curie–Weiss temperature from 25 K in CaCu{sub 3}Ti{sub 4}O{sub 12} without the doping ceramics to 80 K in the composite with 5% of SrFe{sub 12}O{sub 19}.« less

Structural and magnetic aspects of La4(Co1-xNix)3O10+δ (0 ≤ x ≤ 1)

NASA Astrophysics Data System (ADS)

Nagell, Marius Uv; Kumar, Susmit; Sørby, Magnus H.; Fjellvåg, Helmer; Olafsen Sjåstad, Anja

2015-10-01

The Ruddlesden-Popper (RP3) type oxides, La4Co3O10+δ and La4Ni3O10+δ, form a complete solid solution. Powder X-ray and neutron diffraction data show that La4(Co1-xNix)3O10+δ is isostructural to the monoclinic La4Co3O10+δ structure (P21/a) described for all compositions without any further structural distortions as suggested in the literature. A slight elongation of the Co/Ni-O bonds facing the rock salt interlayer occurs for Ni-rich compositions. The magnetic properties of the solid solution series are mapped in the temperature range from 4 to 300 K, and the results are presented in a magnetic phase diagram. Three regimes with antiferromagnetic order (AF) exist at low temperatures, TN < 10 - 30 K. For x = 0.00, the AF is ascribed to Co(II), whereas a broader AF regime around x = 0.50 is ascribed mainly to Ni(II). Pauli paramagnetism is observed close to metallic La4Ni3O10+δ, x > 0.80. The possibility to tune the oxidation state of the transition metal atoms is demonstrated for La4Co3O10+δ, and exemplified by weakening of a temperature-induced spin transition at around 480 K.

Raman Study of the Structural Distortion in the Ni 1–xCo xTiO 3 Solid Solution

DOE PAGES

Fujioka, Yukari; Frantti, Johannes; Puretzky, Alexander; ...

2016-09-08

In this paper, Raman spectra were collected on Ni 1–xCo xTiO 3 (0 ≤ x ≤ 1) ilmenite samples as a function of the temperature between 4 and 1200 K. An evident symmetry lowering from the prototype Rmore » $$\\bar{3}$$symmetry is observed. The distortion was largest for the x = 0.40 and 0.50 samples and significantly diminished for small and large values of x. The distortion was preserved in the whole temperature range and, except for the x = 0.50 sample, did not show significant changes. Notably, between 25 and 69 K, distortion of the x = 0.40 sample is accompanied by ferromagnetic order. The direct cation–cation and O-mediated indirect interactions are discussed as mechanisms behind the distortion and magnetic order. A reversible order–disorder phase transformation, assigned to occur between the ilmenite and corundum phases, took place at 973 K in the x = 0.50 sample. Completion of the transformation took over 1 h. Finally, the role of the overlap of Co/Ni and Ti 3d orbitals through O octahedral faces for charge transfer is discussed.« less

Studies on RF sputtered (WO3)1-x (V2O5)x thin films for smart window applications

NASA Astrophysics Data System (ADS)

Meenakshi, M.; Sivakumar, R.; Perumal, P.; Sanjeeviraja, C.

2016-05-01

V2O5 doped WO3 targets for RF sputtering thin film deposition were prepared for various compositions. Thin films of (WO3)1-x (V2O5)x were deposited on to glass substrates using these targets. Structural characteristics of the prepared targets and thin films were studied using X-ray diffraction. Laser Raman studies were carried out on the thin films to confirm the compound formation.

Polycrystalline (TbXY1-X)2O3 Faraday rotator.

PubMed

Ikesue, Akio; Aung, Yan Lin; Makikawa, Shinji; Yahagi, Akira

2017-11-01

We have succeeded for the first time in synthesizing an optical grade (Tb X Y 1-X ) 2 O 3 (X=0.5-1.0) ceramic Faraday rotator, which greatly exceeds the basic characteristics of the commercial terbium gallium garnet (TGG) (Tb 3 Ga 5 O 12 ) crystal. The Faraday rotation angle increased as the Tb concentration increased, and the Verdet constant increased from 2.1 (82  rad T -1  m -1 at X=0.5) to 3.8 times (154  rad T -1  m -1 at X=1.0) than the TGG single crystal, which is regarded as highest class. Therefore, it is possible to minimize the Faraday rotator length and the magnet in building an optical isolator. It was also confirmed that its optical quality was very comparable to the commercial TGG crystal.

Shielding properties of 80TeO2-5TiO2-(15-x) WO3-xAnOm glasses using WinXCom and MCNP5 code

NASA Astrophysics Data System (ADS)

Dong, M. G.; El-Mallawany, R.; Sayyed, M. I.; Tekin, H. O.

2017-12-01

Gamma ray shielding properties of 80TeO2-5TiO2-(15-x) WO3-xAnOm glasses, where AnOm is Nb2O5 = 0.01, 5, Nd2O3 = 3, 5 and Er2O3 = 5 mol% have been achieved. Shielding parameters; mass attenuation coefficients, half value layers, and macroscopic effective removal cross section for fast neutrons have been computed by using WinXCom program and MCNP5 Monte Carlo code. In addition, by using Geometric Progression method (G-P), exposure buildup factor values were also calculated. Variations of shielding parameters are discussed for the effect of REO addition into the glasses and photon energy.

The incommensurately modulated(1 - x)Ta 2O 5· xWO 3, 0 ≤ x ≤ 0.267 solid solution

NASA Astrophysics Data System (ADS)

Schmid, Siegbert; Withers, Ray L.; Thompson, John G.

1992-08-01

The phase(1 - x)Ta 2O 5 · WO 3, 0 ≤ x ≤ 0.267 has been studied by X-ray powder diffraction and transmission electron microscopy. It was previously described as an infinite series of anion-deficient, α-UO 3-type "line phases," with compositions resulting from intergrowths of different blocks made up by small numbers of α-UO 3-type cells. More correctly(1 - x)Ta 2O 5· xWO 3, 0 ≤ x ≤ 0.267 is described as an incommensurately modulated structure with a linearly composition-dependent primary modulation wave-vector qprim. = qb*. The underlying orthorhombically distorted α-UO 3-type parent structure has space group symmetry Cmmm ( a ≈ 6.20-6.14, b ≈ 3.66, c ≈ 3.89-3.85Å). Characteristic extinction conditions imply a superspace group symmetry of P : Cmmmm : s, -1,1. The four previously reported crystal structures in the solid solution field are examined by means of apparent valence calculations. Crystal chemical reasons are proposed for the width of the composition range,0 ≤ x ≤ 0.267, observed for the title phase.

Favorable Concurrence of Static and Dynamic Phenomena at the Morphotropic Phase Boundary of x BiNi0.5Zr0.5O3-(1 -x )PbTiO3

NASA Astrophysics Data System (ADS)

Datta, K.; Neder, R. B.; Chen, J.; Neuefeind, J. C.; Mihailova, B.

2017-11-01

We reveal that concurrent events of inherent entropy boosting and increased synchronization between A - and B -site cation vibrations of an A B O3 -type perovskite structure give rise to a larger piezoelectric response in a ferroelectric system at its morphotropic phase boundary (MPB). It is further evident that the superior piezoelectric properties of x BiNi0.5Zr0.5O3-(1 -x )PbTiO3 in comparison to x BiNi0.5Ti0.5O3-(1 -x )PbTiO3 are due to the absolute flattening of the local potentials for all ferroelectrically active cations with a higher spontaneous polarization at the MPB. These distinctive features are discovered from the analyses of neutron pair distribution functions and Raman scattering data at ambient conditions, which are particularly sensitive to mesoscopic-scale structural correlations. Altogether this uncovers more fundamental structure-property connections for ferroelectric systems exhibiting a MPB, and thereby has a critical impact in contriving efficient novel materials.

The O VI Mystery: Mismatch between X-Ray and UV Column Densities

NASA Astrophysics Data System (ADS)

Mathur, S.; Nicastro, F.; Gupta, A.; Krongold, Y.; McLaughlin, B. M.; Brickhouse, N.; Pradhan, A.

2017-12-01

The UV spectra of Galactic and extragalactic sightlines often show O VI absorption lines at a range of redshifts, and from a variety of sources from the Galactic circumgalactic medium to active galactic nuclei (AGN) outflows. Inner shell O VI absorption is also observed in X-ray spectra (at λ =22.03 Å), but the column density inferred from the X-ray line was consistently larger than that from the UV line. Here we present a solution to this discrepancy for the z = 0 systems. The O II Kβ line {}4{S}0\\to {(}3D)3{p}4P at 562.40 eV (≡22.04 Å) is blended with the O VI Kα line in X-ray spectra. We estimate the strength of this O II line in two different ways, and show that in most cases the O II line accounts for the entire blended line. The small amount of O VI equivalent width present in some cases has column density entirely consistent with the UV value. This solution to the O VI discrepancy, however, does not apply to high column-density systems like AGN outflows. We discuss other possible causes to explain their UV/X-ray mismatch. The O VI and O II lines will be resolved by gratings on board the proposed mission Arcus and the concept mission Lynx, and would allow the detection of weak O VI lines not just at z = 0, but also at higher redshift.

Characterization of Y1-xCaxBa2Cu4O8 (x=0.0˜ 0.1) with Double Cu-O Chains by Raman Spectra

NASA Astrophysics Data System (ADS)

Kodama, Yasuharu; Tanemura, Sakae; Ikeda, Teruki

1991-08-01

Raman spectra of Y1-xCaxBa2Cu4O8 (x=0.0, 0.02, 0.05 and 0.1) ceramic samples synthesized under high oxygen pressure were investigated. Seven clear peaks assigned to Ag modes were observed for the sample with x=0. With increasing x, the peaks at 238 cm-1, 332 cm-1, 430 cm-1 and 590 cm-1 were broadened. The origin of the broadening of the peaks at 238 cm-1 and 590 cm-1 is considered to be the destruction of the double Cu-O chains due to the substitution of Ca for Y.

Growth and luminescent properties of Lu 2SiO 5:Ce and (Lu 1- xGd x) 2SiO 5:Ce single crystalline films

NASA Astrophysics Data System (ADS)

Zorenko, Yu.; Gorbenko, V.; Savchyn, V.; Voznyak, T.; Grinyov, B.; Sidletskiy, O.; Kurtsev, D.; Fedorov, A.; Baumer, V.; Nikl, M.; Mares, J. A.; Beitlerova, A.; Prusa, P.; Kucera, M.

2011-12-01

Single crystalline films (SCF) of Lu 2SiO 5:Ce (LSO:Ce), (Lu 1- xGd x) 2SiO 5:Ce (LGSO:Ce) and LGSO:Ce,Tb orthosilicates with thickness of 2.5-21 μm were crystallized by liquid phase epitaxy method onto undoped LSO substrates from melt-solution based on PbO-B 2O 3 flux. The concentration of Gd was varied in the range of x=0.2-0.7 formula units (f.u.). In the case of LGSO:Ce SCF growth we do not use any additional doping for reducing the misfit between the SCF and substrate lattices. The luminescence and scintillation properties of LSO:Ce, LGSO:Ce and LGSO:Ce,Tb SCFs were mutually compared and confronted with the performance of reference LSO:Ce and LYSO:Ce crystals. With increasing Gd content the luminescence spectrum of LGSO:Ce SCF is gradually red-shifted with respect to that of LSO:Ce SCF. The LY of (Lu 1- xGd x)SO:Ce SCF becomes lower in comparison with that for LSO:Ce SC at increasing Gd content in the range of x=0.2-0.7 f.u. The peculiarities of luminescence properties of LSO:Ce and LGSO:Ce SCFs in comparison with crystal analogs are explained by the different distribution of Ce 3+ over Lu1 and Lu2 positions of LSO host and by the influence of Pb 2+ contamination coming from the flux used for the film growth.

Temperature Dependence of the Tunneling Conductance in Ba_1-xK_xBiO_3

NASA Astrophysics Data System (ADS)

Miyakawa, N.; Ozyuzer, L.; Zasadzinski, J. F.

1997-03-01

Tunneling measurements have been made on high-density polycrystalline pellets of Ba_1-xK_xBiO3 using a point contact method. The temperature dependence (up to 30 K) and magnetic field dependence (up to 6T) of the tunneling conductance has been measured. It is found that at temperatures less than 4.2 K the gap region conductance can be fit with a BCS density of states (dos) and thermal smearing only. However, as the temperature is increased a quasiparticle recombination rate, Γ, which increases as T^n (n ~ 3) must be included in the dos to fit the data. The behavior of Γ (T) does not follow the strong-coupling theory of Kaplan et al. (S.B. Kaplan et al. Phys. Rev. B 14), 4854 (1976) We investigate whether this anomalous power law dependence can come out of Eliashberg theory using the electron-phonon spectral function, a^2F(ω) for Ba_1-xK_xBiO_3.

Cation disorder in MgX2O4 (X = Al, Ga, In) spinels from first principles

NASA Astrophysics Data System (ADS)

Jiang, Chao; Sickafus, Kurt E.; Stanek, Christopher R.; Rudin, Sven P.; Uberuaga, Blas P.

2012-07-01

We have performed first-principles density functional theory calculations to investigate the possible physical origins of the discrepancies between the existing theoretical and experimental studies on cation distribution in MgX2O4 (X = Al, Ga, In) spinel oxides. We show that for MgGa2O4 and MgIn2O4, it is crucial to consider the effects of lattice vibrations to achieve agreement between theory and experiment. For MgAl2O4, we find that neglecting short-range order effects in thermodynamic modeling can lead to significant underestimation of the degree of inversion. Furthermore, we demonstrate that the common practice of representing disordered structures by randomly exchanging atoms within a small periodic supercell can incur large computational error due to either insufficient statistical sampling or finite supercell size effects.

Electronic transition in La1-xSrxTiO3

NASA Astrophysics Data System (ADS)

Hays, C. C.; Zhou, J.-S.; Markert, J. T.; Goodenough, J. B.

1999-10-01

The transition with increasing x in La1-xSrxTiO3 from an antiferromagnetic, p-type polaronic conductor to an n-type metal with an enhanced Pauli paramagnetism was investigated by monitoring changes in structure, magnetic properties, and, under different hydrostatic pressures, the resistance and thermoelectric power of ceramic samples. We conclude that LaTiO3 is an itinerant-electron antiferromagnet and the transition is first order with a phase separation associated with cooperative oxygen-atom displacements that segregate strongly correlated states from Fermi-liquid states. The Néel temperature TN~145 K decreases precipitously to 100 K at the phase limit x=0.045+/-0.005 the two-phase domain extends over the compositions 0.045<=x<=0.08.

Giant piezoelectric property of (110) oriented BaxSr1-xTiO3 films

NASA Astrophysics Data System (ADS)

Chen, Z. H.; Chen, Z.; Qiu, J. H.; Yuan, N. Y.; Ding, J. N.

2017-10-01

A phenomenological Landau-Devonshire theory is applied to investigate the phase diagrams and physical properties of (110) oriented BaxSr1-xTiO3 films. New ferroelectric phases, such as the tetragonal a1 phase and the orthorhombic a2 c phase, appear in the ;misfit strain-temperature; phase diagrams for (110) oriented films compared with that of (001) oriented films. Moreover, the orthorhombic a2 c phase, and the tetragonal c phase and the triclinic γ phase are stable at low temperature for x = 0.5 and x = 0.7 , respectively. The ferroelectric, dielectric, and piezoelectric properties strongly depend on the misfit strain and electric field. (110) oriented Ba0.7Sr0.3TiO3 film has the larger ferroelectric polarization and piezoelectric coefficient than that of Ba0.5Sr0.5TiO3 film. The giant piezoelectric coefficient of 340 pm / V is obtained at the electric field of 50 KV / cm in (110) oriented Ba0.7Sr0.3TiO3 film, which is comparable with the values of Pb (Zr1-xTix)O3 and (1 - x) Pb (Mg1/3Nb2/3)O3 -xPbTiO3 films. It makes (110) oriented BaxSr1-xTiO3 films suitable for applications in electromechanical devices.

Electronic self-organization in the single-layer manganite $$\\rm Pr_{1-x}Ca_{1+x}MnO4$$

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Feng; Chi, Songxue; Fernandez-Baca, Jaime A

We use neutron scattering to investigate the doping evolution of the magnetic correlations in the single-layer manganitemore » $$\\rm Pr_{\\it 1-x}Ca_{\\it 1+x}MnO_4$$, away from the $x=0.5$ composition where the CE-type commensurate antiferromagnetic (AF) structure is stable. We find that short-range incommensurate spin correlations develop as the system is electron doped ($x<0.5$), which coexist with the CE-type AF order. This suggests that electron doping in this system induces an inhomogeneous electronic self-organization, where commensurate AF patches with $x=0.5$ are separated by electron-rich domain walls with short range magnetic correlations. This behavior is strikingly different than for the three-dimensional $$\\rm Pr_{\\it 1-x}Ca_{\\it x}MnO_3$$, where the long-range CE-type commensurate AF structure is stable over a wide range of electron or hole doping around $x=0.5$.« less

FABRICATION AND OPTOELECTRONIC PROPERTIES OF MgxZn1-xO ULTRATHIN FILMS BY LANGMUIR-BLODGETT TECHNOLOGY

NASA Astrophysics Data System (ADS)

Tang, Dongyan; Feng, Qian; Jiang, Enying; He, Baozhu

2012-08-01

By transferring MgxZn1-xO sol and stearic acid onto a hydrophilic silicon wafer or glass plate, the Langmuir-Blodgett (LB) multilayers of MgxZn1-xO (x:0, 0.2, 0.4) were deposited. After calcinations at 350°C for 0.5 h and at 500°C for 3 h, MgxZn1-xO ultrathin films were fabricated. The optimized parameters for monolayer formation and multilayer deposition were determined by the surface pressure-surface (Π-A) area and the transfer coefficient, respectively. The expended areas of stearic acid with MgxZn1-xO sols under Π-A isotherms inferred the interaction of stearic acid with MgxZn1-xO sols during the formation of monolayer at air-water interface. X-ray diffraction (XRD) was used to determine the crystal structures of MgxZn1-xO nanoparticles and ultrathin films. The surface morphologies of MgxZn1-xO ultrathin films were observed by scanning probe microscopy (AFM). And the optoelectronic properties of MgxZn1-xO were detected and discussed based on photoluminescence (PL) spectra.

Single-vortex pinning and penetration depth in superconducting NdFeAsO 1-xF x

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jessie T.; Kim, Jeehoon; Huefner, Magdalena

2015-10-12

We use a magnetic force microscope (MFM) to investigate single vortex pinning and penetration depth in NdFeAsO 1-xF x, one of the highest-T c iron-based superconductors. In fields up to 20 Gauss, we observe a disordered vortex arrangement, implying that the pinning forces are stronger than the vortex-vortex interactions. We measure the typical force to depin a single vortex, F depin ≃ 4.5 pN, corresponding to a critical current up to J c ≃ 7×10 5 A/cm 2. As a result, our MFM measurements allow the first local and absolute determination of the superconducting in-plane penetration depth in NdFeAsO 1-xFmore » x, λ ab = 320 ± 60 nm, which is larger than previous bulk measurements.« less

Fabrication of Lead-free (K0.5Na0.5)1- x Ag x NbO3 Ferroelectric Ceramics and Their Dielectric Properties

NASA Astrophysics Data System (ADS)

Byun, Jaeduk; Hyun, June Won; Kim, Yeon Jung; Bobor, Kristóf

2018-03-01

In this study, lead-free (K0.5Na0.5)1- x Ag x NbO3 ( x = 0.00, 0.10, 0.15, 0.20, 0.25, and 0.30) ferroelectric ceramics were fabricated using solid-state synthesis without A-site and B-site manufacturing step. The (K0.5Na0.5)1- x Ag x NbO3 ceramics were sintered at 1110 °C for 4 h after calcination at 800 °C for 3 h. The sintered sample was dense, and the grain size was 1.02 7.8 μm. For x ≤ 0.2, the sintered ceramic samples had a single perovskite structure. The temperature dependence of the dielectric constant in the (K0.5Na0.5)1- x Ag x NbO3 was measured at 1 kHz using an LCR meter. The high dielectric constant properties could be obtained in (K0.5Na0.5)1- x Ag x NbO3 ceramics. The orthorhombic-to-tetragonal phase transition temperature and ferroelectric Curie temperature decreased linearly with increasing mole fraction of the Ag content. The Curie temperature shifted from 393 °C for (K0.5Na0.5)NbO3 ceramics to 317 °C for (K0.5Na0.5)0.7Ag0.3NbO3 ceramics. The maximum dielectric constant was 8930 at 330 °C in the (K0.5Na0.5)0.8Ag0.2NbO3 ceramics.

Composition-driven magnetic and structural phase transitions in Bi1-xPrxFe1-xMnxO3 multiferroics