Bixbyite Structure Research Articles

Topotactic Oxidation Pathway of ScTiO3 and High-Temperature Structure Evolution of ScTiO3.5 and Sc4Ti3O12-Type Phases

The novel oxide defect fluorite phase ScTiO(3.5) is formed during the topotactic oxidation of ScTiO(3) bixbyite. We report the oxidation pathway of ScTiO(3) and structure evolution of ScTiO(3.5), Sc(4)Ti(3)O(12), and related scandium-deficient phases as well as high-temperature phase transitions between room temperature and 1300 °Cusing in-situ X-ray diffraction. We provide the first detailed powder neutron diffraction study for ScTiO(3). ScTiO(3) crystallizes in the cubic bixbyite structure in space group Ia3 (206) with a = 9.7099(4) Å. The topotactic oxidation product ScTiO(3.5) crystallizes in an oxide defect fluorite structure in space group Fm3m (225) with a = 4.89199(5) Å. Thermogravimetric and differential thermal analysis experiments combined with in-situ X-ray powder diffraction studies illustrate a complex sequence of a topotactic oxidation pathway, phase segregation, and ion ordering at high temperatures. The optimized bulk synthesis for phase pure ScTiO(3.5) is presented. In contrast to the vanadium-based defect fluorite phases AVO(3.5+x) (A = Sc, In) the novel titanium analogue ScTiO(3.5) is stable over a wide temperature range. Above 950 °C ScTiO(3.5) undergoes decomposition with the final products being Sc(4)Ti(3)O(12) and TiO(2). Simultaneous Rietveld refinements against powder X-ray and neutron diffraction data showed that Sc(4)Ti(3)O(12) also exists in the defect fluorite structure in space group Fm3m (225) with a = 4.90077(4) Å. Sc(4)Ti(3)O(12) undergoes partial reduction in CO/Ar atmosphere to form Sc(4)Ti(3)O(11.69(2)).

Dehydration of 1,5-pentanediol over rare earth oxides

Vapor-phase catalytic dehydration of 1,5-pentanediol was investigated over rare earth oxides (REOs) at 325–450°C. The conversion of 1,5-pentanediol over REOs calcined at 700 and 800°C was higher than that calcined at 500°C. Sc2O3, Yb2O3, and Lu2O3 with cubic bixbyite structure showed the selectivity to 4-penten-1-ol with higher than 74mol%, while REOs with hexagonal and monoclinic structures showed the selectivity with less than 50mol%. Especially, Yb2O3 and Lu2O3 calcined at 1000°C showed high formation rate of 4-penten-1-ol per specific surface area over 1mmolh−1m−2 at 400°C. In the Yb2O3 catalyst calcined at 800°C, the conversion of 1,5-pentanediol was increased up to 74.4mol% with increasing contact time, together with stable selectivity to 4-penten-1-ol of 71.8mol%. In comparing the reactivity of alkanediols to form the corresponding unsaturated alcohols over Yb2O3, we found the reactivity of alkanediols into the corresponding unsaturated alcohols was the following order: 1,4-butanediol>1,3-diols≫1,5-pentanediol≫1,6-hexanediol.

Polyvinyl alcohol–In2O3 nanocomposite films: synthesis, characterization and gas sensing properties

Poly(vinyl alcohol) (PVA)–In2O3 (with 1 and 5 wt% In2O3 loading) nanocomposite films have been prepared by a solvent-casting technique. The In2O3 nanoparticles used in this work were prepared by nonhydrolytic alcoholysis ester elimination reaction of indium acetate in the presence of oleic acid and oleyl alcohol at 220 °C. X-Ray diffraction (XRD) patterns and transmission electron microscopy (TEM) studies indicate that the In2O3 nanocrystals obtained in this work are nearly monodisperse, highly crystalline with cubic bixbyite structure without the presence of any other impurity phase. The PVA–In2O3 nanocomposite films have been structurally characterized by XRD, Fourier transform infrared (FTIR) and Raman spectroscopy. The results confirm the incorporation of In2O3 nanocrystals in the PVA matrix and interactions between In2O3 nanocrystals and PVA molecules. The thermal properties of nanocomposite films have been investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermo-oxidative degradation temperature of PVA increases with the addition of In2O3 nanocrystals and the degree of crystallinity of the PVA matrix decreases in the presence of In2O3 nanocrystals in the nanocomposite films. The room temperature sensing characteristics of the naocomposite films have been studied for various gases, namely, H2S, NH3, CH3, CO, and NO. The PVA–In2O3 nanocomposite films show maximum sensitivity for H2S gas with fast response and reversibility. The response mechanism of the nanocomposite films to various gases is also proposed.

Anatase TiO2 and ITO co-sputtered films for an indium-saving multicomponent electrode in organic solar cells

We report the characteristics of a Ti–In–Sn–O (Ti–ITO) multicomponent electrode prepared by co-sputtering of ITO and anatase TiO2 targets for reducing high-cost indium content in the anode layer of organic solar cells (OSCs). The dependence of electrical, optical, structural, and surface properties of the Ti–ITO multicomponent electrodes on the RF power was investigated in detail. The optimized Ti–ITO (80W TiO2 co-sputtered ITO) electrode exhibited a low sheet resistance of 18.06Ω/square, a high average optical transmittance of 80.61% and a root mean square roughness of 2.40nm. The anatase TiO2 phase in the ITO matrix prevents the bixbyite structure from attaining the preferred orientation, producing a smooth surface of the Ti–ITO electrode. Moreover, the OSC with the optimized Ti–ITO anode showed an open circuit voltage (0.60V), short circuit current (8.33mA/cm2), fill factor (63.99%) and power conversion efficiency (3.18%) comparable to those of OSCs with a reference ITO electrode. This indicates that the Ti–ITO multicomponent electrode is a promising indium-saving multicomponent electrode that to reduces the indium content in ITO electrodes for low-cost OSCs.

Phase transitions of (Cu,Ni)3TeO6 solid solutions

(Cu,Ni)3TeO6 solid solutions with the bixbyite (pseudocorundum) and ilmenite structures have been prepared by solid-state reactions and characterized by a variety of techniques. We have studied the effect of nickel substitution for copper on the phase composition of the materials, examined the microstructure of ceramic samples, and measured their magnetic susceptibility, heat capacity, permittivity, and loss tangent as functions of temperature. This allowed us to reveal dielectric anomalies related to structural phase transitions and to determine the antiferromagnetic ordering temperatures of the (Cu,Ni)3TeO6 ceramics.

STUDY OF STRUCTURAL AND MAGNETIC PROPERTIES OF Co-DOPED In2O3 NANOPARTICLES

In the present work, we have prepared Co doped In2O3 nanoparticles using co-precipitation method. The prepared nanoparticles were characterized by the X-ray diffraction, scanning electron microscopy and dc magnetization hysteresis loop measurements. From the X-ray diffraction analysis it observed that all sample exhibits single phase polycrystalline nature. All the diffraction lines correspond to the bixbyite cubic structure. The full width half maximum (FWHM) calculated from XRD pattern has been found to decrease with increase in the Co contents, indicating that particle size decreases with increase in the Co concentration. FE–SEM micrograph reflects the nanocrystalline behavior of all the samples and shows that doping of Co ions hinders growth of the particles. DC magnetization measurements reveal that Co -DOPED In2O3 samples exhibits room temperature ferromagnetism.

Room temperature ferromagnetism in Ni doped In 2O 3 nanoparticles

In the present work, Ni doped In 2O 3 nanoparticles were prepared using simple co-precipitation method. From the x-ray diffraction analysis it is observed that all samples exhibit single phase polycrystalline nature. All the diffraction lines correspond to the bixbyite type cubic structure. A UV visible analysis reveals that optical band gap decreases from 4.63 to 3.84 eV with Ni doping. DC magnetization measurements reveal that Ni doped In 2O 3 nanoparticles exhibit room temperature ferromagnetism.

Impurity Centers in Oxides Investigated by γ-γ Perturbed Angular Correlation Spectroscopy and <i>Ab Initio</i> Calculations

In this chapter Perturbed Angular Correlation (PAC) experiments on binary oxides are described. These experiments provide local-scale fingerprints about the formation, identification, and lattice environment of defect complexes at the PAC probe site. The potential of the PAC observations in conjunction with ab initio calculations is shown. Measurements of the electric-field gradient at impurity sites using 111Cd and 181Ta probes are reviewed. Special attention is paid to oxides with the bixbyite structure. The case of In2O3 is particularly analyzed. Results obtained with HfO2, in form of coarse grain or nano particles, are described. The potential results that can be obtained from Density Functional Theory ab initio calculations in doped systems are shown describing the main results observed in many impurity-host systems.

Structural characterization of amorphous alumina and its polymorphs from first-principles XPS and NMR calculations

We have calculated x-ray photoemission (XPS) spectra and nuclear magnetic resonance (NMR) chemical shifts for amorphous alumina from first principles. We generate models for amorphous structures at three different densities by means of a stochastic quenching procedure. We analyze these structures by calculating radial distribution functions, angle distributions functions, bond lengths, and coordination numbers. Our amorphous models compare well with previous molecular dynamics simulations and experiments. We include in our study, the stable phase of alumina $\ensuremath{\alpha}$, some of the transition phases, that is, $\ensuremath{\theta}$, $\ensuremath{\gamma}$, and $\ensuremath{\kappa}$, and the hypothetical bixbyite structure for comparison. Our results reproduce both XPS spectra and NMR chemical shifts and suggest that the XPS failure to resolve the different local environments in the different phases of alumina is due to the strong ionicity of the Al-O bond. Our calculated NMR chemical shifts show that the local environments are well resolved. We estimate the broadening of the NMR peaks due to local atomic environment differences in the amorphous phase to be as large as 35 ppm.

Effect of Li3+ heavy ion irradiation on the Mo doped In2O3 thin films prepared by spray pyrolysis technique

The high visible–near infrared transparent and high carrier mobility (μ) Mo doped (0.5 at%) indium oxide (IMO) films were deposited by the spray pyrolysis technique. The deposited films were irradiated by 50 MeV Li3+ ions with different fluences of 1 × 1011, 1 × 1012 and 1 × 1013 ions cm−2. X-ray diffraction analysis confirmed the cubic bixbyite structure of indium oxide. A fascinating feature is that the ion irradiation process has introduced a fraction of the molybdenum oxide phase. The μ of as-deposited IMO films is decreased from ∼122.4 to 93.3 cm2 V−1 s−1, following the ion irradiation. The theoretically calculated μ and carrier density values were correlated with those measured experimentally. The transport mechanism has been analysed based on the ionized and neutral impurity scattering centres. The average transmittance (400–2500 nm) of the as-deposited IMO films is decreased from 83% to 60% following irradiation.

Theoretical DFT study of the structure and chemical activity of small indium(III) oxide clusters

The B3LYP/Lanl2dz and B3LYP/SDD levels of DFT have been used to describe the structural properties of small stoichiometric indium(III) oxide clusters. It was shown that the most stable structures for the monomer and dimer are linear and cubic, respectively, in origin. The most stable trimer is due to the formation of three eight-membered and two six-membered rings with alternation of In and O atoms. Among neutral and monocation tetrameric structures, formation of an “arrowhead” isomer is energetically less favorable than the global minimum structure that has eight six-membered and six four-membered rings. In the pentamer and octamer, a few centers of higher coordination number and a variety of In–O bond lengths are observed. The other centers cannot be fitted to the characteristic bixbyite structure, however, so the larger octamer cannot be a good model for mimicking the properties of the In2O3 crystal structure. An H-terminated cluster model consisting of In13O27H15 is proposed that well describes basic features of indium oxide and tin-doped indium oxide (ITO) structures.

Thin-film structure and fluorescence properties of sol-gel-synthesized Y2-xEuxO3 phosphors

Eu-doped yttria (Y2−xEuxO3) thin-film phosphors were prepared using a sol–gel process with post-annealing at 900°C. The Y2−xEuxO3 samples showed cubic bixbyite structure with a gradual increase in the lattice constant (≤0.5%) as x increases (≤0.22). The Eu-doped films exhibited strong photoluminescence (PL) near 2 eV at room temperature with well-resolved fluorescence peaks being ascribed to spin-flip f-f transitions, 5D0 → 7FJ (J = 0, 1, 2, 3, 4, 6), within trivalent Eu3+(f6) ion. Among the six fluorescence lines, the intensity of the strongest 2.03-eV line (J = 2) varies significantly with the Eu content and its optimum value for the maximum PL strength is likely to be near x = 0.1. The Eu-doped films on the Al2O3 substrates exhibited significantly higher PL intensities than those on the Si substrates despite no significant difference in structural properties between the two species being observed. It can be understood by comparing the change of complex refractive index for the Y2−xEuxO3/Al2O3 and Y2−xEuxO3/Si optical systems.

PREPARATION AND CHARACTERIZATION OF TRANSPARENT CONDUCTIVE Ta-DOPED ITO FILMS BY ELECTRON-BEAM EVAPORATION

Tantalum-doped indium tin oxide ( Ta -doped ITO) transparent conductive films are deposited on glass substrates by electron-beam evaporation. The effects of different Ta concentrations and annealing temperatures on the structural, morphologic, electrical, and optical properties of Ta -doped ITO films are investigated by X-ray diffraction (XRD), atomic force microscope (AFM), Hall measurement, and optical transmission spectroscopy. The obtained films are polycrystalline with a cubic bixbyite structure of indium oxide and preferentially oriented in the (222) crystallographic direction. The minimum resistivity of 1.54×10-4 Ω ·cm is obtained from the ITO film containing 0.2 wt% tantalum annealed at 500°C and the average optical transmittance is over 95% from 425 nm to 460 nm.

Improved epitaxy of ultrathin praseodymia films on chlorine passivated Si(111) reducing silicate interface formation

Ultrathin praseodymia films have been deposited on both Cl-passivated and nonpassivated Si(111) substrates by molecular beam epitaxy. Comparative studies on the crystallinity and stoichiometry are performed by x-ray photoelectron spectroscopy, x-ray standing waves, and x-ray reflectometry. On nonpassivated Si(111) an amorphous silicate film is formed. In contrast, praseodymia deposited on Cl-passivated Si(111) form a well-ordered crystalline film with cubic-Pr2O3 (bixbyite) structure. The vertical lattice constant of the praseodymia film is increased by 1.4% compared to the bulk value. Furthermore, the formation of an extended amorphous silicate interface layers is suppressed and confined to only one monolayer.

Investigation of bixbyite type scandium oxides involving a magnetic cation: ()

Presently, the crystal structure and magnetic properties of Sc 2− x Fe x O 3 samples are described for 0.0 ≤ x ≤ 1.0 . The cubic bixbyite structure (space group: Ia-3 ) prevails for all compositions. Excellent homogeneity of the samples was confirmed by energy dispersive spectroscopy analysis performed with a Transmission Electron Microscope. The crystal structure of ScFeO 3 was determined by combined refinements of powder X-ray and neutron diffraction data. The magnetic behavior is typical of a frustrated system and no long range order prevails at 9 K. ► This article is of interest for a better understanding of magnetic diluted Fe–O–Fe interactions. ► Even with Fe/Sc=1, the statistic distribution of cations leads to very high resistivity values. ► Sc 3+ : a natural ferroic cation (3d 0 ) is of interest for discovery of new multiferroic compounds. ► Structural and physical study in the A B O 3 phase diagram.

New‐Phased Metastable V2O3 Porous Urchinlike Micronanostructures: Facile Synthesis and Application in Aqueous Lithium Ion Batteries

New-phased metastable V(2) O(3) porous urchinlike micronanostructures were first fabricated on a large scale by a simple top-down strategy of pyrolyzing a vanadyl ethylene glycolated precursor in the absence of any templates or matrices. The pyrolysis mechanism was clearly revealed by synchrotron vacuum ultraviolet (VUV) photoionization mass spectra for the first time. The new-phased metastable V(2) O(3) exhibits a body-centered cubic bixbyite structure and shows structural evolution from metastable cubic symmetry to thermodynamically stable rhombohedral symmetry V(2) O(3) (R) above 510 °C. Furthermore, the prepared V(2) O(3) porous urchinlike micronanostructures, as anode materials in aqueous lithium ion batteries, exhibit improved electrochemical properties with relatively high first discharge capacity and better cycle retention relative to thermodynamically stable V(2) O(3) (R), which is derived from its unique microscopic crystal structure and macroscopic 3D framework with rigid morphology, porous structure, and high specific surface area.

A novel engineered oxide buffer approach for fully lattice-matched SOI heterostructures

Epitaxial (epi) oxides on silicon can be used to integrate novel device concepts on the canonical Si platform, including functional oxides, e.g. multiferroics, as well as alternative semiconductor approaches. For all these applications, the quality of the oxide heterostructure is a key figure of merit. In this paper, it is shown that, by co-evaporating Y2O3 and Pr2O3 powder materials, perfectly lattice-matched PrYO3(111) epilayers with bixbyite structure can be grown on Si(111) substrates. A high-resolution x-ray diffraction analysis demonstrates that the mixed oxide epi-films are single crystalline and type B oriented. Si epitaxial overgrowth of the PrYO3(111)/Si(111) support system results in flat, continuous and fully lattice-matched epi-Si(111)/PrYO3(111)/Si(111) silicon-on-insulator heterostructures. Raman spectroscopy proves the strain-free nature of the epi-Si films. A Williamson–Hall analysis of the mixed oxide layer highlights the existence of structural defects in the buffer, which can be explained by the thermal expansion coefficients of Si and PrYO3.

Citrate gel process and thermoelectric properties of Ge-doped In 2O 3 bulk ceramics

Indium oxide ceramics doped with different doping levels of germanium (from 0 to 10 at.%) were prepared with nano-sized powders obtained by citrate gel process. Ge for In substitution in the In 2O 3 bixbyite structure below the solubility limit (about 0.5–1 atom%) leads to a large decrease in the electrical resistivity and the absolute value of the Seebeck coefficient. X-ray diffraction and scanning electron microscopy show the presence after sintering of well dispersed secondary phases In 2Ge 2O 7 when the Ge solubility in the In 2O 3 matrix is passed. The thermal properties measurements confirm that the decrease in the lattice thermal conductivity observed in these composite materials can be attributed to the presence of insulating In 2Ge 2O 7 phases. Furthermore, preliminary microwave sintering experiments have been tested in order to keep the nanoscale after sintering. Particular nano–microstructures were obtained due to minimal grain growth induced by this rapid sintering process.

Epitaxial growth and structure of (La1−xLux)2O3 alloys on Si(111)

LaLuO 3 layers are epitaxially grown on Si(111) by molecular beam epitaxy using high temperature effusion sources. Samples are prepared by simultaneous as well as alternating growth of La2O3 and Lu2O3. Grazing incidence x-ray diffraction indicates that the resulting crystal structure of the alloys is cubic. Simultaneous and alternating growth with a monolayer period lead to the same distribution of La and Lu with no preferential ordering. In all cases the lattice mismatch to Si is less than 0.6%. The experimental results are analyzed by studying the energetics of hexagonal, bixbyite, and perovskite (La1−xLux)2O3 crystal structures employing density functional theory.

Synthesis of 3-buten-1-ol from 1,4-butanediol over indium oxide

Dehydration of 1,4-butanediol (14BDO) was investigated over indium oxide. Over the indium oxide prepared by precipitation, both conversion of 14BDO and selectivity to unsaturated alcohol, 3-buten-1-ol (3B1ol), increase with the increase in calcination temperature of indium oxide irrespective of the decrease in the specific surface area. The maximum values of 79.6% conversion and 79.0% selectivity to 3B1ol are obtained over indium oxide calcined at 900 °C. The values are much higher than the activities of commercial indium oxide. The activities of indium oxide depend on the shape of particles. Indium oxides prepared by the precipitation are composed of particles with diameter of 10–70 nm. The size and shape of particles change by calcination: spherical shape at low temperature of <800 °C varies to angular one at >800 °C with a slight growth of particle size. The change in the shape of the particles means that indium oxide crystallites calcined at >800 °C mainly expose 2 2 2 facets. The dehydration reaction of 14BDO to 3B1ol is preferentially promoted over 2 2 2 surface of bixbyite structure.