High-pressure synthesis and local structure of corundum-type In(2-2x)Zn(x)Sn(x)O(3) (x ≤ 0.7)

The corundum-type In(2-2x)Zn(x)Sn(x)O(3) solid solution (cor-ZITO, x ≤ 0.7) was synthesized at 1000 °C under a high pressure of 70 kbar. cor-ZITO is a high-pressure polymorph of the transparent conducting oxide bixbyite-In(2-2x)Zn(x)Sn(x)O(3) (x ≤ 0.4). Analysis of the extended X-ray absorption fine structure suggests that significant face-sharing of Zn and Sn octahedra occurs, as expected for the corundum structure type. In contrast to the ideal corundum structure, however, Zn and Sn are displaced and form oxygen bonds with lengths that are similar to those observed in high-pressure ZnSnO(3). Powder X-ray diffraction patterns of cor-ZITO showed the expected unit cell contraction with increased cosubstitution, but no evidence for ilmenite-type ordering of the substituted Zn and Sn. A qualitative second harmonic generation measurement, for the solid solution x = 0.6 and using 1064 nm radiation, showed that Zn and Sn adopt a polar LiNbO(3)-type arrangement.     

Magnetic and Transport Properties of Bi_(0.5)Ca_(0.5–x)La_xFe_(0.3)Mn_(0.7)O_3(x=0, 0.05, 0.10, 0.15, 0.20, 0.25) Prepared by Molten Salt Method

Polycrystallines Bi0.5Ca0.5–xLaxFe0.3Mn0.7O3(x=0, 0.05, 0.10, 0.15, 0.20, 0.25) were prepared by molten salt method and showed perovskite orthorhombic structure with space group Pnma. The magnetic measurements indicate that the compounds exhibit antiferromagnetic behavior in a temperature range of 4―300 K. The measurements of transport properties suggest that the substitution of La for Ca enhanced the conductivity, and a kink appeared on the curve of temperature dependence of resistivity at 275 K, which is ...     

Phosphates M 0.5(1 + x) 2+ Cr x Ti2 − x (PO4)3: Synthesis, structure, and catalytic properties

Complex phosphates of titanium, chromium, and metals(2+) of the general formula M_{0.5(1 + x} )Cr _x Ti_{2 ? x} (PO₄)₃ (M = Mg, Ca, Mn, Ni, Sr, Ba, and Pb) were synthesized. Their phase formation was studied by means of X-ray powder diffraction, electron probe microanalysis, differential thermal analysis, and IR spectroscopy. Individual phases and solid solutions crystallizing in kosnarite and langbeinite structure types were identified; their crystallographic parameters were calculated. The catalytic properties of phosphates Ca_{0.5(1 + x} )Cr _x Ti_{2 ? x} (PO₄)₃ in methanol conversion were studied.     

Crystal structural, magnetic, and transport properties of layered cobalt oxyfluorides, Sr2CoO(3+x)F(1-x) (0 ≤ x ≤ 0.15)

The crystal structure of the layered cobalt oxyfluoride Sr(2)CoO(3)F synthesized under high-pressure and high-temperature conditions has been determined from neutron powder diffraction and synchrotron powder diffraction data collected at temperatures ranging from 320 to 3 K. This material adopts the tetragonal space group I4/mmm over the measured temperature range and the crystal structure is analogous to n = 1 Ruddlesden-Popper type layered perovskite. In contrast to related oxyhalide compounds, the present material exhibits the unique coordination environment around the Co metal center: coexistence of square pyramidal coordination around Co and anion disorder between O and F at the apical sites. Magnetic susceptibility and electrical resistivity measurements reveal that Sr(2)CoO(3)F is an antiferromagnetic insulator with the Néel temperature T(N) = 323(2) K. The magnetic structure that has been determined by neutron diffraction adopts a G-type antiferromagnetic order with the propagation vector k = (1/2 1/2 0) with an ordered cobalt moment μ = 3.18(5) μ(B) at 3 K, consistent with the high spin electron configuration for the Co(3+) ions. The antiferromagnetic and electrically insulating states remain robust even against 15%-O substation for F at the apical sites. However, applying pressure exhibits the onset of the metallic state, probably coming from change in the electronic state of square-pyramidal coordinated cobalt.     

Hydrates [Na2(H2O)x](2-thiobarbiturate)2 (x = 3, 4, 5): crystal structure,spectroscopic and thermal properties

The hydrates [Na₂(H₂O)₃(Htba)₂] (1) and [Na₂(H₂O)₄(Htba)₂] (2), where H₂tba is 2-thiobarbituric acid, were obtained under different thermal conditions from aqueous solutions and were structurally characterized. The molecular and supramolecular structures were compared to the known structure of [Na₂(H₂O)₅(Htba)₂] (3). In polymeric 1–3, the Htba^? ions are linked to Na⁺ through O and S forming octahedra. The decrease of the number of coordination water molecules led to an increase of the total number of bridge ligands (μ₂-H₂O, Htba^?) and a change of the Htba^? coordination. These factors induced higher distortion of the octahedra. It was assumed that hydrates, with a different number of coordinated water molecules, are more probable when the central metal has weaker bonds with O water molecules and with other ligands. The net topologies of 1–3 were compared. Thermal decomposition and IR spectra were analyzed for 1 and 2.     

LaNi1 − x Cu x O3 (x = 0.05, 0.10, 0.30) coated electrodes for oxygen evolution in alkaline medium

LaNi_1???x Cu _x O₃ (x?=?0.05, 0.10, 0.30) coated electrodes were prepared by brush painting using Ni foam substrates in order to increase its active surface area. For comparison, coatings with x?=?0.05 were also prepared using vitreous carbon substrates. Cyclic voltammetry was used to evaluate the coating roughness (R _f). Values between 5,145?±?148 and 6,334?±?277 were obtained, depending on the x value, for the coatings on Ni foam. These results show that the electrodes prepared with LaNi_1???x Cu _x O₃ powder, obtained at 600 °C, lead to a big increase on the oxide electrode roughness when compared with LaNiO₃ electrodes prepared by a similar method. Much lower values were obtained for the coatings on vitreous carbon indicating that the substrate nature is also a key factor for the preparation of high surface area electrodes. The calculated kinetic parameters for the oxygen evolution reaction (OER) show that the partial replacement of Ni by Cu has no beneficial effect on the intrinsic catalytic activity of the coatings. On the other hand, a big increase on the active area is observed even for small amounts of Cu (x?=?0.05), leading to a better overall OER performance for the LaNi_0.95Cu_0.05O₃ coating on Ni foam. For this composition, the activity is dominated by geometric effects.     

Second-harmonic generating properties of polar noncentrosymmetric aluminoborate solid solutions, Al(5-x)Ga(x)BO9 (0.0 ≤ x ≤ 0.5)

A series of solid solutions of polar aluminoborate materials, Al(5-x)Ga(x)BO(9) (0.0 ≤x≤ 0.5) have been synthesized by standard solid-state reactions using Al(2)O(3), Ga(2)O(5), and B(OH)(3) as reagents. The phase purities, crystal structures, and solid solution behavior of the reported materials have been investigated by powder X-ray diffraction. Solid solutions of Al(5-x)Ga(x)BO(9) crystallize in the polar noncentrosymmetric space group, Cmc2(1), with a three-dimensional structure consisting of distorted MO(4), MO(5), MO(6), and BO(3) polyhedra (M = Al or Ga). Powder second-harmonic generating (SHG) measurements on the Al(5)BO(9) using 1064 nm radiation, indicate the material has a SHG efficiency of approximately 2 times that of α-SiO(2) and is not phase-matchable (type 1). Further nonlinear optical (NLO) measurements on the Al(5-x)Ga(x)BO(9) solid solutions indicate a sharp increase in SHG efficiency up to 10 times that of α-SiO(2) for x≥ 0.4. Close structural examination suggests that the alignment of the asymmetric π-delocalization of BO(3) groups is responsible for the abrupt increase of SHG efficiency.     

Effect of hydration on conductivity of Ba4La x Ca2 − x Nb2O11 + 0.5x (x = 0.5, 1, 1.5, 2) phases

Substitution of Ca by La in initial cubic double perovskite Ba₄(Ca₂Nb₂)O₁₁[VO]₁ allowed obtaining phases with a similar structure with a lower content of structural oxygen vacancies, Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} [VO]_{1 ? 0.5x} (x = 0.5, 1, 1.5, 2). The impedance technique was used to measure the temperature dependences of conductivity in the atmosphere of dry and humid air. Transport numbers determined using the EMF method in an oxygen-air and water steam concentration cells point to the predominantly hole nature of conductivity in the high-temperature region (T > 600°C) and to predominance of proton conductivity in the low-temperature region. Activation energies of hole and proton conductivity were calculated. Thermogravimetric measurements were carried out under heating from 25 to 1000°C with simultaneous mass-spectrometric determination of evolved H₂O and CO₂. The properties of the studied Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} (x = 0.5, 1, 1.5, 2) phases were compared with the earlier studied Ba_{4 ? x} La _x (Ca₂Nb₂)O_{11 + 0.5x} phases with similar lanthanum content.     

Kinetics of phase transition and thermal stability in Se80?x Te20Zn x (x?=?2, 4, 6, 8, and 10) glasses

Se_80?x Te₂₀Zn _x (x?=?2, 4, 6, 8, and 10) glasses have been prepared using conventional melt quenching technique. The kinetics of phase transformations (glass transition and crystallization) have been studied using differential scanning calorimetry (DSC) under non-isothermal condition at five different heating rates in these glasses. The activation energy of glass transition (E _t), activation energy of crystallization (E _c), Avrami exponent (n), dimensionality of growth (m), and frequency factor (K _o) have been investigated for the better understanding of growth mechanism using different theoretical models. The activation energy is found to be highly dependent on Zn concentration. The rate of crystallization is found to be lowest for Se₇₀Te₂₀Zn₁₀ glassy alloy. The thermal stability of these glasses has been investigated using various stability parameters. The values of these parameters were obtained using characteristic temperatures, such as glass transition temperature T _g, onset crystallization temperature T _c, and peak crystallization temperature T _p. In addition to this, enthalpy-released during crystallization has also been determined. The values of stability parameters show that the thermal stability increases with the increase in Zn concentration in the investigated glassy samples.     

Synthesis and electrical properties of variable-composition phases Rb1 − x A1 − x R1 + x (MoO4)3 (0 ≤ x ≤ 0.2; A = Mg, Mn, Co, Ni; R = Sc, Yb, Lu)

Subsolidus region of the ternary systems Rb₂MoO₄-AMoO₄-R₂(MoO₄)₃, in which variable-composition phases Rb_{1 ? x} A_{1 ? x} R_{1 + x} (MoO₄)₃ crystallizing in the monoclinic system (space group C2) are formed, was studied. Their crystallographic parameters were calculated; temperature dependences of the electrical conductivity, dielectric constant, and dielectric loss tangent were analized.     

Rubidium-cationic conductivity of Rb2−2x Ga2−x A x O4 (A = P, V, Nb, Ta) solid electrolytes

Solid solutions based on rubidium monogallate RbGaO₂ with a general formula Rb_2?2x Ga_2?x A _x O₄ (A = P, V, Nb, and Ta) are synthesized. Their crystal structure and temperature and concentration dependences of conductivity are studied. The highest rubidium-cationic conductivity is (1.8–3.9) × 10^?3 S cm^?1 at 400°C and (1.4–2.1) × 10^?2 S cm^?1 at 700°C. These results are compared with the data for rubidium monogallate doped with four-charged cations and solid solutions based on RbAlO₂.     

Sol-gel synthesis and structure of MZr2(AsO4)3 arsenates and MZr2(AsO4) x (PO4)3 − x arsenate phosphates (M = K,Rb, Cs)

MZr₂(AsO₄)₃ arsenates and MZr₂(AsO₄) _x (PO₄)_{3 ? x} arsenate phosphates (M = K, Rb, Cs) have been obtained by sol-gel synthesis followed by heat treatment and have been characterized by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Continuous series of substitutional solid solutions form in the MZr₂(AsO₄) _x (PO₄)_{3 ? x} systems (0 ≤ x ≤ 3). The solid solutions have a kosnarite structure (KZr₂(PO₄)₃, space group \(R\bar 3c\) ). The crystal structures of MZr₂(AsO₄)₃ and MZr₂(AsO₄)_1.5(PO₄)_1.5 have been refined by full-profile analysis. The structural frameworks of these phases are built from ZrO₆ octahedra and AsO₄ tetrahedra or (As,P)O₄ tetrahedra statistically populated by arsenic and phosphorus atoms. The alkali metal atoms occupy extraframework sites. The effect of the crystal chemical properties of alkali metals on the formation of the structures of MZr₂(AsO₄)₃ arsenates (M = Li-Cs) and MZr₂(AsO₄) _x (PO₄)_{3 ? x} solid solutions is discussed.     

Electroconductivity of Solid Solutions Cs3–2x M x PO4 (M = Ba, Sr, Ca, Mg)

Solid solutions Cs_{3 – 2x} M _x PO₄ (M = Ba, Sr, Ca, Mg) are synthesized and their thermal behavior and electroconductivity are examined. Adding elements of Subgroup IIA of the periodic table into cesium orthophosphate shifts the phase transition, which occurs in pure Cs₃PO₄ at 450–620°, towards lower temperatures and raises the cesium cation conductivity at low temperatures. The electroconductivity of a high-temperature modification of Cs₃PO₄ is weakly dependent on the presence and concentration of such additives, which points to structural disordering of the cesium sublattice.     

F+ and F⁻ affinities of simple N(x)F(y) and O(x)F(y) compounds

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for the neutral and ionic N(x)F(y) and O(x)F(y) systems using coupled cluster theory with single and double excitations and including a perturbative triples correction (CCSD(T)) method with correlation consistent basis sets extrapolated to the complete basis set (CBS) limit. To achieve near chemical accuracy (±1 kcal/mol), three corrections to the electronic energy were added to the frozen core CCSD(T)/CBS binding energies: corrections for core-valence, scalar relativistic, and first order atomic spin-orbit effects. Vibrational zero point energies were computed at the CCSD(T) level of theory where possible. The calculated heats of formation are in good agreement with the available experimental values, except for FOOF because of the neglect of higher order correlation corrections. The F(+) affinity in the N(x)F(y) series increases from N(2) to N(2)F(4) by 63 kcal/mol, while that in the O(2)F(y) series decreases by 18 kcal/mol from O(2) to O(2)F(2). Neither N(2) nor N(2)F(4) is predicted to bind F(-), and N(2)F(2) is a very weak Lewis acid with an F(-) affinity of about 10 kcal/mol for either the cis or trans isomer. The low F(-) affinities of the nitrogen fluorides explain why, in spite of the fact that many stable nitrogen fluoride cations are known, no nitrogen fluoride anions have been isolated so far. For example, the F(-) affinity of NF is predicted to be only 12.5 kcal/mol which explains the numerous experimental failures to prepare NF(2)(-) salts from the well-known strong acid HNF(2). The F(-) affinity of O(2) is predicted to have a small positive value and increases for O(2)F(2) by 23 kcal/mol, indicating that the O(2)F(3)(-) anion might be marginally stable at subambient temperatures. The calculated adiabatic ionization potentials and electron affinities are in good agreement with experiment considering that many of the experimental values are for vertical processes.     

Electronic structure and related properties for quasi-binary (GaP)1−x (ZnSe) x crystals

The results of pseudopotential calculations of the band structure and related electronic and optical properties of quasi-binary (GaP)_1?x (ZnSe) _x crystals in the zinc blende structure are presented. Trends in bonding and ionicity are discussed in terms of electronic charge densities. Moreover, the composition dependence of the refractive index and dielectric constants are reported. The computed values are in reasonable agreement with experimental data. The results suggest that for a proper choice of the composition x, (GaP)_1?x (ZnSe) _x could provide more diverse opportunities to achieve the desired electronic and optical properties of the crystals which would improve the performances of devices fabricated on them.     

Two-step hydrothermal synthesis of submicron Li(1+x)Ni(0.5)Mn(1.5)O(4-δ) for lithium-ion battery cathodes (x = 0.02, δ = 0.12)

A facile two-step hydrothermal method is developed for the large-scale preparation of lithium nickel manganese oxide spinel as a cathode material for lithium ion batteries. In the reaction, nickel is introduced in a first step at neutral pH, followed by lithium insertion under base to form a product having composition Li(1.02)Ni(0.5)Mn(1.5)O(3.88). The X-ray diffraction pattern and Raman spectroscopy of the synthesized material support a cubic Fd3m structure in which Ni and Mn are disordered on the 16d Wyckoff site, necessary for good cycling characteristics. XP spectroscopy and elemental analysis confirms that Mn remains reduced in the final product (Z(Mn) = 3.82) and that two different chemical environments for Ni exist on the surface. SEM imaging shows a primary particle size of ~200 nm, and galvanostatic cycling of the material vs. Li(+/0) gives a reversible gravimetric capacity of ~120 mA h g(-1) at 1 C rate (147 mA g(-1)) with reversible cycling up to 1470 mA g(-1), supported by rapid Li(+) diffusion. The capacity fade at 1 C is substantial, 17.3% over the first 100 cycles between 3.4 and 5.0 V. However, when the voltage limits are altered, the capacity retention is excellent: nearly 100% when cycled either between 3.4 and 4.4 V (where oxygen vacancies are not electrochemically active) or 89% when cycled between 4.4 and 5.0 V (where the Jahn-Teller active Mn(4+/3+) couple is not accessed).     

Small angle neutron scattering experiments on solid electrolyte (AgI) x (AgPO3)1−x

Superionic conductor glasses have generated considerable technological interest in the applications such as batteries, fuel cell, sensors, etc. In AgPO₃ glass doped by AgI, (AgI) _x (AgPO₃)_1?x , small size of AgI clusters were formed and dispersed in the AgPO₃ glass. The size of clusters in the sample depends on the AgI content and influences the electrical properties of the sample. To understand the microscopic structure, in particular the shape and size of the clusters, a series of small angle neutron scattering experiment on (AgI) _x (AgPO₃) _x with x?=?0.0, 0.5, and 0.7 were performed at the Neutron Scattering Laboratory–National Nuclear Energy Agency, Indonesia. By assuming the clusters are spherical, a radius of gyration R _g of the clusters was determined from a Guinier plot. As there are different clusters sizes in the samples, a polydisperse model is also used to analyze the data. The results show that the average radius of clusters dispersed in (AgI) _x (AgPO₃)_1?x samples with x?=?0.0, 0.5, and 0.7 are around 236.2, 252.6, and 257.5 Å, respectively.     

Electroconductance of single-crystal Li2 + x Fe 2 − 2x 2+ Fe x 3+ (MoO4)3 (x = 0.22)

Electrophysical properties of single-crystal Li_{2 + x} Fe _{2 ? 2x} ²⁺ Fe _x ³⁺ (MoO₄)₃ (x = 0.22) are studied at 25–400°C. It is found that the conduction is of electronic nature and the conductivity equals 5 × 10^-2 S/cm at 300°C. The activation energy for the electron transport is 0.23 eV. The conductance in molybdate Li_2.22Fe _1.56 ²⁺ Fe _0.22 ³⁺ (MoO₄)₃ is markedly anisotropic.