The electronic structure and properties of Ni1−xLixO1−y (0⩽x⩽1/4, 0⩽y⩽1/8)

The electronic structures of NiO, Ni_0.875O, NiO_0.875, Ni_0.875Li_0.125O, Ni_0.875Li_0.125O_0.875 and Ni_0.75Li_0.25O_0.875 with a NaCl-type crystal structure have been calculated using the ab initio linear muffin-tin orbitals method in the LSDA+U approximation. The effect of vacancies in the metal and metalloid sublattices and lithium ions on parameters of the NiO electronic spectrum (the energy gap and the valence band widths, etc.) has been analyzed. It is shown that the defects like the dipole LiV_O and the tripole LiV_OLi impaired stability and could reduce electrical conductivity of the nickel–oxide-based phases.     

Ionic conductivity and crystal chemistry of ramsdellite type compounds,Li2+x(LixMg1−xSn3)O8, 0 ≤ x ≤ 0.5 and Li2Mg1−xFe2xSn3−xO8, 0 ≤ x ≤ 1

Solid solution phases Li_2+x(Li_xMg_1−xSn₃)O₈: 0 ≤ x ≤ 0.5 and Li₂Mg_1−xFe_2xSn_3−xO₈: 0 ≤ x ≤ 1, both with ramsdellite type structure, have been synthesized by solid state reaction at 1773 and 1523 K, respectively. The relationship of the ramsdellite structure to the recently illustrated, tetragonal-packed structure is given. The Li_2+x(Li_xMg_1−xSn₃)O₈ solid solutions exhibit conductivities 4 × 10⁻⁶–5 × 10⁻⁴ (Ω cm)⁻¹ at 573 K and corresponding activation energies, 0.93−0.74 eV. The highest conductivity was observed for Li_2.3(Li_0.3Mg_0.7Sn₃)O₈, x = 0.3. In the solid solution series Li₂Mg_1−xFe_2xSn_3−xO₈, the highest conductivity was exhibited by Li₂Fe₂Sn₂O₈, 2 × 10⁻⁵ (Ω cm)⁻¹ at 573 K.     

Ca3(P x V1 − x O4)2: Eu3+ nanophosphor synthesis, controlled microstructure, and photoluminescence

In this paper, Eu³⁺-doped Ca₃(P _x V_{1 ? x} O₄)₂ (x = 0.1, 0.4, 0.7) nanophosphors were synthesized in the presence of sodium dodecyl benzene sulfonate (SDBS). The products present interesting and regular morphologies under the mild conditions. For Ca₃(P _x V_{1 ? x} O₄)₂: Eu³⁺, they have the similar phase and their morphologies vary with the content ratio of P to V. Furthermore, the luminescence behavior of Eu³⁺ has been investigated in this one kinds of matrices. In Ca₃(P _x V_{1 ? x} O₄)₂: Eu³⁺, the ⁵ D ₀-⁷ F ₂ emissions of Eu³⁺ were the strongest, indicating that the Eu³⁺ site is without inversion symmetry, the host compositions with different molar ratio of P to V have; great influence on the luminescent performance. Among those products, The value of I ₆₁₅/I ₅₉₃ for Eu³⁺ in Ca₃(P_0.7V_0.3O₄)₂ host lattice is the biggest. The substitution of PO ₄ ^3? for VO ₄ ^3? increase the ratio of surface Eu cations as well as the value of I ₆₁₅/I ₅₉₃ of Eu³⁺.     

High pressure synthesis and structure of a novel clathrate-type compound: Te7+xSi20−x (x∼2.5)

A novel clathrate-type compound, Te_7+xSi_20+x (x∼2.5), has been synthesized from the elements under high pressure and high temperature conditions. Its structure has been solved by Rietveld analysis of the XRD powder patterns combined with the results of an electron diffraction study. This structure is closely related to that of a type I clathrate, but with a different unit-cell parameter (a∼2×a₀) and space group (Fd-3c instead of Pm-3n). Its main feature is that it corresponds to a double clathration of a Te atom enclosed in a partially Te substituted (12.5%) Si₂₀ pentagonal dodecahedra, which is itself enclosed in a large Te₂₄ polyhedron, in form of a truncated octahedron. This outer Te network proved to be similar to the characteristic H₂O host lattice of a type VII clathrate (HEF₆·(H₂O)₅·HF (E=P, As, Te)), the distribution of the Si/Al atoms in minerals of the sodalite group ((Na,Ca)₈(Al₆Si₆O₂₄)(Cl,S,SO₄)₂) and to the arrangement of the Ba atoms in the structure of the superconducting compound, Ba₆C₆₀. This new clathrate structure of silicon is the first one which exhibits Si₂₀ pentagonal dodecahedra which are only linked by inter-cluster bonds, a result which opens new prospects in the domain of the chemistry of macro-ions such as Si₂₀¹²⁺ or Si₂₈⁴⁺.     

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.     

Synthesis and crystal structure of Mo6−x Nb x I11 (x = 1–1.5)

A solid solution Mo_{6 ? x} Nb _x I₁₁ (x = 1.1–1.5) containing cluster cores {Mo₅NbI₈} is obtained by the high-temperature reaction of molybdenum, niobium, and iodine (550°C, 70 h, quartz ampule). According to the X-ray diffraction data, heating at 800°C in a molybdenum container results in the decomposition of the solution to Mo₆I₁₂ and Nb₆I₁₁. According to the X-ray structure analysis data, the compounds are isostructural to the high-spin modification Nb₆I₁₁ (space group Pccn). The presence of Nb atoms in the structure changes the structural type from the layered (Mo₆I₁₂) to framework structure, noticeably increases the metalmetal distances (2.661–2.716 Å, 2.695 Å) Mo₆ octahedron with the retention of the distance from the metal (M) to the μ₃-“capped” I atoms, and strongly elongates the M₆-I-M₆ bridges almost to the value observed in Nb₆I₁₁.     

Structural and dynamical studies of δ-Bi2O3 oxide ion conductors: I. The structure of (Bi2O3)1−x(Y2O3)x as a function of x and temperature

We report the results of both Bragg and diffuse neutron scattering studies of the superionic solid solution, (Bi₂O₃)_1−x(Y₂O₃)_x. The Bragg data for polycrystalline samples show that the strutural features observed previously in (Bi₂O₃)_0.73(Y₂O₃)_0.27 are present across the entire range of the solid solution, 0.25 < x < 0.42. The number of 〈111〉-displaced anions in the defect fluorite structure decreases with increasing Y³⁺ content whereas the extent of short-range ordering on the anion sublattice increases. Both of these observations are consistent with the decrease in oxide ion conductivity which occurs as x increases. The basic crystal structure does not change between room temperature and 1023 K, although the unit cell volume increases by 3.78% for x = 0.27, and the number of 〈111〉-displaced anions increases, again consistent with the enhanced conductivity observed at high temperatures. It is suggested that Y³⁺ stabilizes the fluorite structure by ordering the vacancies on the oxygen sublattice in chains along the 〈111〉 and 〈110〉 directions.     

A porous Cu(II)-MOF containing [PW12O40]3− and a large protonated water cluster: synthesis,structure, and proton conductivity

A proton-conducting metal–organic framework (MOF), {[Cu₄(dpdo)₁₂][H(H₂O)₂₇(CH₃CN)₁₂][PW₁₂O₄₀]₃}_n (where dpdo is 4,4′-bipyridine-N,N′-dioxide) (1), was synthesized by the reaction of CuHPW₁₂O₄₀·nH₂O and dpdo at room temperature. Single-crystal X-ray diffraction analysis at 293?K revealed that 1 crystallized in the cubic space group Im-3 and presented a non-interwoven 3-D framework with cubic cavities and guest molecules. A large ionic water cluster H⁺(H₂O)₂₇, consisting of a water shell (H₂O)₂₆ and an encaged H⁺(H₂O) as a center core, was trapped in the cubic cavity of the MOF {[Cu₄(dpdo)₁₂(PW₁₂O₄₀)₃]^?}_∞. Thermogravimetric analysis suggests that 1 has high thermal stability, indicating that such a non-interwoven 3-D framework with cubic cavities is a suitable host for researching protonated water clusters. Its water vapor adsorption isotherm at room temperature and pressure shows that the water vapor adsorbed in it was 65.1 cm^3?g^?1 at the maximum allowable humidity. It exhibits good proton conductivities of 10^?5–10^?4?S^?cm^?1 at 100 °C in the relative humidity range 35–98%.     

(NixMg1−x)10Ge3O16: A new phase with structure related to olivine and spinel

A new compound, (Ni_xMg_1−x)₁₀Ge₃O₁₆(x ⋍ 0.4−0.5), has been identified at atmospheric pressure in the NiO-MgO-GeO₂ system. Its unit cell is rhombohedral with the (hexagonal) parametersa = 5.887(1)A˚, c = 28.603(4)A˚, andZ = 3 for a phase with the Ni₄Mg₆Ge₃O₁₆ composition. A structural model has been derived from powder X-ray diffraction data: theM₁₀Ge₃O₁₆(M =Ni + Mg) structure results from a regular intergrowth of {111} layers of the spinel and rock-salt structures. It can also be described as an intergrowth of (001) olivine layers (Pnma setting) with {111} layers of a cation-deficient rock-salt structure. Due to its close relationship to both spinel and olivine, theM₁₀Ge₃O₁₆(M =Ni + Mg) structure could possibly occur at the phase boundary involved in the polymorphic olivine ⇄ spinel transformation.     

Sol–gel synthesis, crystal structure, electronic properties and magnetic studies of B2+xAsxCo4−3xO7 (0.0 ≤ x ≤ 0.75) composites

Synthesis of B_2+xAs_xCo_4?3xO₇ (S1–S4: x = 0.0, 0.25, 0.50 and 0.75) composite oxides were performed by sol–gel method. The powder X-ray diffraction pattern and Reitveld refinement results revels that the samples are formed monoclinic phase with Z = 2 and space group P₂₁/m. Average crystallite size of the samples determined by Scherrer’s relation are found to be ~28–50 nm. The observed and calculated density values are determined and compared. Thermogram shows no phase transition in the range of 50–1,000 °C. The scanning electron micrographs show the morphology of the samples which are observed, the crystallites are rod like shape. The purity and the quantitative analysis were examined by the energy dispersive X-ray. The B–O and Co–O bonds of different sites show marginal variation in the samples, the circular valence charge density contour map of the Co and O in S1–S4 show partial covalent nature of Co–O. Based on the plane-wave density functional theory calculations on crystal structure for band structure and density of states of sample S1–S4 using CASTEP programme package show all the samples are conductor with no band gap. The magnetic moment plot in the range ±10 kG indicates the weak ferromagnetic behavior of the samples. The electron paramagnetic resonance line shapes of all four (S1–S4) samples are isotropic, Diffuse reflectance spectra of sample S1–S4 at room temperature show the band around 273 nm is ligand to metal (O^2? → Co²⁺) charge transfer transition and d–d transition around 570 nm, respectively.     

Thermal and X-ray investigations of the quasi-binary system Ag1−xPdxMg (if0 ⩽ x ⩽ 0.5)

It is shown by X-ray diffraction, thermal analysis and microscopy studies that the quasi-binary system Ag_1−xPd_xMg crystallizes with a CsCltype structure and forms single-phase alloys throughout the temperature range investigated. The lattice constants follow Vegard's law. They are described by a = a₀ − bx where a₀ = 331.526 pm and b = 15.756 pm.     

Influence of Ca2+ substitution on thermal,structural, and conductivity behavior of Bi1−xCaxFeO3−y (0.40 ≤ x ≤ 0.55)

Bi_1?xCa_xFeO_3?y (0.40 ≤ x ≤ 0.55) perovskite oxides have been synthesized by solid-state reaction method to study their properties as a cathode material for intermediate temperature solid oxide fuel cells. The as prepared samples were characterized by X-ray diffraction, differential thermal analyzer/thermogravimetry, dilatometer, and impedance spectroscopy to study their structural, thermal, and electrical properties. The Rietveld refinement results confirmed that all the samples exhibit tetragonal structure with P4mm space group. In addition to this, sample x = 0.55 exhibits Ca₂Fe₂O₅ as a secondary phase. It has been observed that lattice parameters decrease with increase in calcium content. The thermal expansion coefficient and ionic conductivity increases with increase in calcium content up to x = 0.50. The highest ionic conductivity is observed for Bi_0.5Ca_0.5FeO_3?y i.e. 1.71 × 10^?2 S cm^?1.     

Eu3+/Eu2+ redox energy in a new lithium intercalation compound LixEuTa7O19 (0 ≤ x ≤ 1)

Journal of Solid State Electrochemistry - Electrochemical lithium intercalation is observed in LixEuTa7O19 with 0 ≤ x ≤ 1; the voltage profiles show a 4f6/4f7 Eu3+/Eu2+ redox plateau at...