Ta Compounds Research Articles

Immersed effects of Ta and Zr compounds on activity of oxygen reduction reaction in sulfuric acid

The immersed effects of Ta and Zr compounds (Ta–CNO and Zr–CNO) on the activity of oxygen reduction reaction (ORR) have been investigated in the sulfuric acid. The concentration of Zr on Zr–CNO was higher than that of Pt on Pt black. The concentration of Ta on Ta–CNO was almost the same as that of Pt on Pt black in sulfuric acid. The catalytic activity of Zr–CNO for the ORR decreased with time. In contrast, the catalytic activity of Ta–CNO for the ORR was maintained up to 1050 h in the sulfuric acid.

(CuCl)LaTa2O7and quantum phase transition in the (CuX)LaM2O7family (X=Cl, Br;M=Nb, Ta)

We apply neutron diffraction, high-resolution synchrotron x-ray diffraction, magnetization measurements, electronic structure calculations, and quantum Monte-Carlo simulations to unravel the structure and magnetism of (CuCl)LaTa2O7. Despite the pseudo-tetragonal crystallographic unit cell, this compound features an orthorhombic superstructure, similar to the Nb-containing (CuX)LaNb2O7 with X = Cl and Br. The spin lattice entails dimers formed by the antiferromagnetic fourth-neighbor coupling J4, as well as a large number of nonequivalent interdimer couplings quantified by an effective exchange parameter Jeff. In (CuCl)LaTa2O7, the interdimer couplings are sufficiently strong to induce the long-range magnetic order with the Neel temperature TN~7 K and the ordered magnetic moment of 0.53 mu_B, as measured with neutron diffraction. This magnetic behavior can be accounted for by Jeff/J4~1.6 and J4~16 K. We further propose a general magnetic phase diagram for the (CuCl)LaNb2O7-type compounds, and explain the transition from the gapped spin-singlet (dimer) ground state in (CuCl)LaNb2O7 to the long-range antiferromagnetic order in (CuCl)LaTa2O7 and (CuBr)LaNb2O7 by an increase in the magnitude of the interdimer couplings Jeff/J_4, with the (CuCl)LaM2O7 (M = Nb, Ta) compounds lying on different sides of the quantum critical point that separates the singlet and long-range-ordered magnetic ground states.

Catalytic Activity and Stability of Ta Compounds for Oxygen Reduction Reaction

not Available.

Ta Compound Film as New Anode Material for Polymer Electrolyte Water Electrolysis

In order to attempt Ta compounds as anode electrocatalyst for Polymer electrolyte water electrolysis, the catalytic activities of Ta compound films for the oxygen evolution reaction (OER) was investigated. Ta compound films were prepared under several partial pressures of nitrogen and oxygen at several temperatures by reactive sputtering. Although Ta compound films had high overpotential for the OER, the catalytic activities of Ta compounds for the OER were changed by the change of preparation condition.

Hydration and proton conductivity in LaAsO4

Incorporation and transport of protonic defects have been studied in nominally undoped and 1 and 3 mol% Sr-doped LaAsO4 prepared by a co-precipitation route. AC impedance of the materials was measured as a function of temperature (1150 to 400 °C), pO2 (1 to 1 × 10−5 atm) and pH2O (0.025 to 3 × 10−5 atm). The bulk conductivities generally decrease with decreasing temperature and moreover with decreasing pH2O within the whole temperature range. At the highest temperatures, a small decrease in the conductivity with decreasing pO2 was also observed. The defect structure of Sr-doped LaAsO4 appears to be dominated by oxygen vacancies in the form of pyroarsenate ions, As2O4−7, in dry atmospheres at high temperatures and by protonic defects in the form of hydrogen arsenate ions, HAsO2−4, in wet atmospheres. A significant isotope effect shows that protons contribute to the total conductivity at all temperatures under wet conditions and predominate at temperatures below ∼850 °C. The remaining contributions are attributed to oxide ions and electron holes. The extracted hydration thermodynamics are comparable to those determined for other LnXO4 (X = P, V, Nb, Ta) compounds, and the enthalpy of mobility of protons (86 ± 5 and 88 ± 5 kJ mol−1 for the 1 and 3 mol% doped samples, respectively) follows an apparent trend for the isostructural LaXO4 (X = P, As, V) series with the enthalpy of mobility of protons decreasing with increasing radius of the X-site cation. However, the partial proton conductivities of Sr-doped LaAsO4 are lower than those determined for acceptor doped LaPO4 and LaVO4 for which the possible reasons are discussed.

X-ray Emission Spectroscopy of Ta-Related Oxides

We performed X-ray emission spectroscopy (XES) by using a double crystal spectrometer. Ta-Lα1 and Lα2 emission lines of Ta-related materials of Ta-metal, Ta2O5, LiTaO3, and KTaO3 were measured. XES is one of the most important spectroscopies to make a remarkable progress utilizing third generation synchrotron radiation sources. Here, we discuss some aspects of XES in Ta compounds of recent experimental data. We also discuss an azimuth dependence of partial fluorescence yield spectra (PFY) of a single-crystal KTaO3. The precise measurement by the double crystal spectrometer has revealed a change of the PFY spectrum by changing the crystal orientation, especially in the white line region.

4-3-3 Ta-Ti共添加系α-Fe_2O_3光電極触媒による太陽光水分解性能の顕著な向上(4-3 光触媒・水素製造,Session4 新エネルギー,研究発表)

4-3-3 Ta-Ti共添加系α-Fe_2O_3光電極触媒による太陽光水分解性能の顕著な向上(4-3 光触媒・水素製造,Session4 新エネルギー,研究発表)

Photophysical and Photocatalytic Properties of Zn3M2O8 (M = Nb, Ta)

The Zn3M2O8 (M = Nb, Ta) compounds with layered crystal structures were prepared by a conventional solid‐state reaction method, and their electronic‐band structures, optical properties, and photocatalytic activities were investigated. The prepared compounds were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis diffuse reflectance, and Mott–Schottky measurement. The UV–Vis diffuse reflectance spectra revealed Zn3Nb2O8 and Zn3Ta2O8 exhibited band gaps of 4.1 and 4.5 eV, respectively. From the electronic‐band‐structure calculations using DFT method, it was found that the valence band in both compounds was constructed by the hybridization of Zn 3d and O 2p orbitals, whereas the conduction band was consisted of Nb 4d (Zn3Nb2O8) and Ta 5d (Zn3Ta2O8) orbitals. The photocatalytic activity of both compounds was examined by the measurement of the H2 production rate in an aqueous methanol solution under UV light irradiation. The Zn3Ta2O8 with a larger band gap exhibited higher activity than Zn3Nb2O8, which was attributed to its higher reduction potential resulting from the difference of its electronic‐band configuration.

Evaluation of Ta and Zr Compounds for Oxygen Evolution Reaction in Sulfuric Acid

In order to reduce the cost of anode material for polymer electrolyte water electrolysis, the oxygen evolution reaction (OER) of Ta and Zr compounds film was investigated in sulfuric acid. Both Ta and Zr compounds film on an etched Ti rod was prepared by the reactive sputtering under various conditions which partial pressure of oxygen and nitrogen, and base material temperature were varied. The parameter of peusdo-current density which was related to the active area was defined as i*(= i⋅QA-1), where QA was the anodic electric charge calculated from cyclic voltammogram, and applied for the pseudo-OER specific activity. As a result, the pseudo-OER activity of steady state (iSS.*) on Ta compounds film prepared under the optimal condition as same as that of IrO2. iSS.* of Zr compounds film prepared under optimal condition was higher than that of IrO2.

Acoustic wave propagation in Ni3 R (R = Mo, Nb, Ta) compounds

The ultrasonic properties of the hexagonal closed packed structured Ni3Mo, Ni3Nb and Ni3Ta compounds were studied at room temperature for their characterization. For the investigations of ultrasonic properties, the second-order elastic constants using Lennard–Jones potential were computed. The velocities V 1 and V 2 have minima and maxima respectively at 45° with the unique axis of the crystal, while V 3 increases with respect to angle with the unique axis of the crystal. The inconsistent behaviour of angle-dependent velocities is associated with the action of second-order elastic constants. Debye average sound velocities of these compounds increase with the angle and has maximum at 55° with the unique axis at room temperature. Hence, when a sound wave travels at 55° with the unique axis of these materials, the average sound velocity is found to be maximum. The results achieved are discussed and compared with the available experimental and theoretical results.

Ring folding in cyclopentadienyl diazabutadiene complexes of group 4 and 5 transition metals

The syntheses of CpM( i-PrDAB) 2 (M = Nb, Ta; Cp = (C 5H 5); i-PrDAB = bis-isopropyl-1,4-diazabuta-1,3-diene) are reported. Both show fluxional NMR spectra indicating that the two DAB rings differ. The X-ray crystal structure of CpNb( i-PrDAB) 2 shows one ring to be more folded than the other. Density functional calculations have been used to investigate the degree of folding of the chelate ring in the compounds Cp 2M(R-DAB), (M = Ti, Zr, Hf, Nb, Ta; R = H, i-Pr; DAB = 1,4-diazabuta-1,3-diene) and CpM(R-DAB) 2 (M = Nb and Ta). For Cp 2M(R-DAB) the group 4 compounds all have folded rings whereas the Nb and Ta compounds have planar rings. In all compounds the rings are reduced and the folding is driven by the electron number requirements of the metal centre.

Density functional study of the structural, electronic, elastic and thermodynamic properties of ACRu 3 ( A = V, Nb and Ta) compounds

Using a density functional scheme, we have investigated for the first time the structural, electronic, elastic and thermal properties of the ideal cubic antiperovskite carbides ACRu 3 ( A = V, Nb, Ta). The computed equilibrium lattice constants are in excellent agreement with the experimental data. The electronic band structures and densities of states profiles show that the studied compounds are conductors. Analysis of atomic site projected local density of states reveals that the bonding character may be described as a mixture of covalent–ionic and, due to the d states in the vicinity of the Fermi level, metallic. Pressure dependence up to 50 GPa of the single crystal and polycrystalline elastic constants has been investigated in details. Analysis of the B/ G ratios shows that VCRu 3 is slightly brittle while NbCRu 3 and TaCRu 3 are slightly ductile. We have estimated the sound velocities in the principal directions. Through the quasi-harmonic Debye model, in which the phononic effects are taken into account, the temperature and pressure effects on the lattice constant, bulk modulus, heat capacity and Debye temperature are performed.

New Oxyfluoride Pyrochlores Li2–xLa(1+x)/3□(2x–1)/3B2O6F (B = Nb, Ta): Average and Local Structure Characterization by XRD, TEM and 19F Solid‐State NMR Spectroscopy

AbstractTwo new solid solutions Li2–xLa(1+x)/3□(2x–1)/3B2O6F (B = Ta, Nb) have been synthesized in powder form by solid‐state synthesis. Their composition domain corresponds to 0.6 ≤ x ≤ 1.1 for the Ta compounds and to 0.7 ≤ x ≤ 1.0 for the Nb compounds. The structural study has been performed by XRD on two single crystals with the compositions Li1.00La0.67□0.33Ta2O6F and Li1.25La0.58□0.17Nb2O6F. It shows that both structures adopt the pyrochlore type A2B2X6X′ structure [SG: Fd$\bar {3}$m, Z = 8, a = 10.448(1) Å for the Ta compound and a = 10.448(7) Å for the Nb compound]. The BO6 octahedra built the classical pyrochlore [B2X6]2– array, while the F– ions are strictly ordered on the 8b positions, which correspond to the centre of the pyrochlore cages. The Li+, La3+ ions and vacancies located in the hexagonal tunnels are assumed to occupy statistically the A sites in the 16d position. The local structure has been more precisely studied by HREM and 19F solid‐state NMR techniques. The HREM study reveals significant population fluctuations in the 16d site. 19F MAS NMR spectroscopy evidences six different environments for the fluoride ion, [FLi3□] (or [FLi4]), [FLi3La], [FLi2La□], [FLi2La2], [FLiLa2□] and [FLa2□2], whereas fifteen different types of environment are expected if a random distribution of Li+, La3+ and vacancies in the 16d site is assumed. The solid solution composition domains are limited for the highest Li+ ions content (low x value) and for the highest La3+ ions and vacancies content (high x value) because of the low stability of environments rich in Li+ or La3+ ions. It has been shown that La(Li)–F distances decrease with the CN of F– ions, from [FLi3La] to [FLi2La□] and from [FLi2La2] to [FLa2□2] environments. Fluoride ions occupying tetrahedra involving vacancies are brought closer to the corners occupied by Li+ and/or La3+. Finally, the stability of the oxyfluoride pyrochlore phases is discussed.

Evaluation of Ta and Zr compounds for Oxygen Evolution Reaction in Sulfuric Acid

not Available.

Effect of Various Additives on the Oxidation Behavior of ZrB2‐Based Ultra‐High‐Temperature Ceramics at 1800°C

The effect of various additives such as TiB2, HfB2, CrB2, TaB, TaSi2, LaB6, La2O3, and AlN on the oxidation behavior of ZrB2‐based ultra‐high‐temperature ceramics (UHTCs) at 1800°C was investigated. The additions of CrB2 and HfB2 to the ZrB2–SiC composites have minor effect on the structure evolution of the oxide scale and oxidation resistance. However, all the other additives, especially for Ti and Ta compounds, have changed the oxidation mechanism resulting in a marked detrimental effect on the oxidation resistance of ZrB2‐based UHTCs.

Lattice dynamical and thermodynamical properties of HfB2 and TaB2 compounds

Abstract We have investigated the structural parameters (the lattice constants and bond length) and phonon dispersion relations in XB 2 (X = Hf, Ta) compounds using the first-principles total energy calculations. The generalized gradient approximations are used to model exchange–correlation effects. Our secondary results on the temperature-dependent behavior of thermodynamical properties such as entropy, heat capacity, internal energy, and free energy are also presented for the same compounds. The obtained results are in good agreement with the available experimental and other theoretical data.

Evolution of metal-compound residues on the walls of plasma etching reactor and their effect on critical dimensions of high-k/metal gate

It was found that critical dimensions of high-k/metal gates obey the multivariate linear approximation with the precision of 3σ=±0.86nm, whose explanatory variables are amounts of metal compounds remaining on the plasma reactor walls. To measure their amounts, the authors assumed they are proportional to amounts of atoms sputtered out by Ar plasma and falling onto a Si wafers placed on a wafer stage. In this study, effects of metal compounds of W, Ti, Ta, and Hf, which are used to construct full-metal/high-k gates, were measured. It was found that Ti and Ta compounds dominate the fluctuation of critical dimensions and the dependency of their amount on wafer numbers being etched obeys a simple difference equation. From these results, they can estimate and minimize the fluctuations of critical dimensions in mass fabrications.

Phase equilibria and chemical vapor transport in the system Mo–Ta–As

The phase diagram Mo–Ta–As was studied in two partial isothermal sections at 1050 °C (in the As-rich corner) and at 1400 °C (As-poor alloys) using powder X-ray diffraction and electron probe microanalysis. A complete solid solution was found to exist between isostructural Mo 5As 4 and Ta 5As 4 and the ternary solubility of Mo in Ta 3As at 1400 °C was determined. A ternary phase Mo x Ta 1− x As with MnP-type structure was found to exist in the As-rich part of the system. Lattice parameters were investigated as a function of composition for (Mo,Ta) 5As 4 and for Mo x Ta 1− x As. Additional experiments of chemical vapor transport (CVT) from 1000 °C to 900 °C using different ternary source compositions and I 2 and Br 2 (PtBr 2) as transport agents were performed. Only Ta compounds were found in the sink and no ternary transport was observed.

Electronic band structures of AV2 (A = Ta,Ti, Hf and Nb) Laves phase compounds

First-principles density functional calculations, using the all-electron fullpotential linearized augmented plane wave method, have been performed inorder to investigate the structural and electronic properties for Laves phaseAV2 (A = Ta,Ti, Hf and Nb) compounds. The generalized gradient approximation and theEngel–Vosko-generalized gradient approximation were used. Our calculations showthat these compounds are metallic with more bands cutting the Fermi energy(EF) as we move from Nb to Ta, Hf and Ti, consistent with theincrease in the values of the density of states at the Fermi levelN(EF).N(EF) is controlled by the overlapping of V-p/d, A-d and A-p states around the Fermi energy.The ground state properties of these compounds, such as equilibrium lattice constant, arecalculated and compared with the available literature. There is a strong/weak hybridizationbetween the states, V-s states are strongly hybridized with A-s states below and aboveEF. Around the Fermi energy we notice that V-p shows strong hybridization with A-p states.

Carboxylate-intercalated layered double hydroxides aged under microwave–hydrothermal treatment

Carboxylate-intercalated (terephthalate, TA and oxalate, ox) layered double hydroxides (LDHs) are aged under a microwave–hydrothermal treatment. The influence of the nature of the interlayer anion during the ageing process is studied. Characterization results show that the microwave–hydrothermal method can be extended to synthesize LDHs with anions different than carbonate, like TA. LDH–TA compounds are stable under microwave irradiation for increasing periods of time and the solids show an improved order both in the layers and in the interlayer region as evidenced by powder X-ray diffraction (PXRD), 27Al MAS NMR and FT-IR spectroscopy. Furthermore, cleaning of the surface through removal of some organic species adsorbed on the surface of the particles also occurs during the microwave–hydrothermal treatment. Conversely, although the expected increase in crystallinity is observed in LDH–ox samples, the side-reaction between Al 3+ and ox is also enhanced under microwave irradiation, and a partial destruction of the structure takes place with an increase in the M 2+/M 3+ ratio and consequent modification of the cell parameters.