Synthesis,structure, and conduction of solid solutions BIMEVOX (Me = Cu,Ti)

Conditions for synthesizing single-phase solid solutions Bi₄V_{2 ? x} Cu _x/2Ti _x/2O_{11 ? x} and Bi_{4 ? x/2}V_{2 ? x/2}Cu _x/2Ti _x/2O_{11 ? x/2} are studied. The sequence of phase transformations is determined. Possible domains of stability of polymorphic modifications and the overall conductivity as a function of temperature and composition are studied. The structure of the γ-modification is refined using Rietveld’s full-profile analysis.     

Crystal structure and conduction of BICUTIVOX

Existence boundaries, structure, and transport parameters were studied for Bi₄V_{2 ? x} Cu _x/2Ti _x/2O_{11 ? x} solid solutions. Doping levels within x = 0.025–0.15 distort the C2/m crystal lattice (this lattice is characteristic of individual the Bi₄V₂O₁₁ phase) and lowers its symmetry to triclinic. The solid solutions with 0.25 ≤ x ≤ 0.30 crystallize in tetragonal space group I4/mmm. High-temperature X-ray diffraction and dilatometry measurements for Bi₄V_{2 ? x} Cu _x/2Ti _x/2O_{11 ? x} (x ≤ 0.35) solid solutions verified the existence of three structural varieties within 298–1023 K. Electrical conductivity of BICUTIVOX was studied by impedance spectroscopy as a function of temperature, composition, and oxygen partial pressure. Equivalent circuits of cells were analyzed. Features of electrical conductivity versus temperature for the structural varieties are noted. Above 873 K, the solid solutions samples with x = 0.05 have the highest conductivity. At lower temperatures, higher conductivities are in the solid solutions that retain the γ phase in the low-temperature region. The dominant oxygen-ion conduction mechanism was discovered in the solid solutions.     

Synthesis processes and transport properties of solid solutions in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-GeO<Subscript>2</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The results of studies of solid solutions with the overall composition of Bi₄V_{2 ? x} Ge _x O_{11 ? δ} and Bi₄Ge_{3 ? x} V _x O_{12 + δ} are presented. The process of phase formation are studied during the synthesis of solid solution using the ceramic method and through liquid precursors. Crystallochemical parameters of the obtained compounds are determined. The size distribution of the particles is studied. Conductivity of annealed of polycrystalline samples as a function of temperature and composition is studied using the impedance spectroscopy method. The shape of impedance complex plane plots of the samples obtained in different ways is studied and analyzed.     

Structure and properties of solid solutions based on bismuth niobate Bi<Subscript>3</Subscript>NbO<Subscript>7</Subscript>

Solid solutions Bi₃Nb_1–yW_yO_{7 ± δ}, Bi₃Nb_1–yV_yO_{7 ± δ}, Bi₃Nb_1–yFe_yO_{7 ± δ} (y = 0.1–0.5; Δy = 0.1), and Bi_3–xY_xNb_1–yW_yO_{7 ± δ} (x = 0.05, 0.1; y = 0–0.3; Δy = 0.1) have been studied. The homogeneity ranges of the solid solutions and crystal-chemical parameters have been determined by means of X-ray powder diffraction. The electrical conductivity of sintered samples has been studied by impedance spectroscopy. The joint introduction of yttrium and tungsten into the niobium sublattice does not lead to an increase in the conductivity of solid solutions, and the change of the dopant type has no noticeable effect on this conductivity.     

Formation of Nd<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Bi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3</Subscript> Nanocrystals under Conditions of Glycine-Nitrate Synthesis

Nd_1–xBi_xFeO₃ nanocrystals with crystallite size 30?60 nm have been prepared under conditions of glycine–nitrate burning. Single-phase Nd_1–xBi_xFeO₃ nanocrystals are formed over the entire studied concentrations range if the glycine–nitrate synthesis is performed in excess of the oxidizer. Under these conditions, a continuous range of the Nd_1–xBi_xFeO₃ solid solutions (0 ≤ х ≤ 0.75) crystallized in the rhombic system (space group Pbnm) are formed without crystallization of the burning intermediates. The Nd_1–xBi_xFeO₃ solid solutions (х = 0.775, 0.8) crystallize in the rhombic system (space group Pbаm).     

Investigation of the α-BiO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>F<Subscript>3 − 2<Emphasis Type="Italic">y</Emphasis></Subscript>-based tysonite-type solid solutions by X-ray diffraction and impedance spectroscopy

Tysonite solid solutions Bi_{1 ? x} M _x (O, F)_{3 ? d} (M = Na, Sr, or Nd) based on α-BiO _y F_{3 ? 2y} were prepared by solid-state synthesis at 873 K with subsequent quenching to ice-cold water. Aliovalent substitutions in both the cation and anion sublattices (M ⁿ⁺ → Bi³⁺ and O^2? → F^?) made it possible to vary the anion-vacancy density. The solid solutions were characterized by X-ray diffraction and impedance spectroscopy. The homogeneity regions for the tysonite solid solution were determined; triangulation schemes at 873 K were suggested for the systems BiF₃-BiOF-NaBiF₄ and BiF₃-BiOF-SrF₂, and a scheme of the subsolidus phase diagram for the system BiO_0.1F_2.8-NdF₃ was suggested. In the system BiO_0.1F_2.8-NdF₃, the transition temperature from the low-symmetry tysonite phase (phase II, space group P \(\overline 3 \) c1, Z = 6) to the high-symmetry one (phase I, space group P6₃/mmc, Z = 2) decreases with increasing anion-vacancy density. Conductivity measurements were performed in the temperature range 300–523 K and the frequency range from 5 to 1 × 10⁶ Hz. The conductivity of samples in the system BiO_0.1F_2.8-NdF₃ increases with increasing bismuth-ion and anion-vacancy concentrations.     

Substituted bismuth vanadates and chromates: New aspects

The work is devoted to the synthesis and attestation of a number of substituted vanadates and chromates of bismuth. For bismuth vanadates of the BIMEVOX family, the homogeneity regions of the Bi₄V_{2 – x}Cr _x O_{11 ± d} solid solutions have been refined, the features of the structure change of the compounds with increasing chromium content and changing temperature have been noted, and the powders and ceramics have been studied by electron microscopy. For the first time, as an impurity, an individually substituted bismuth chromate of the composition Substituted bismuth chromate of the Bi₁₃Cr_{5 – y}V _y O_{34.5 – d} (y = 0.95 ± 0.05) composition has been detected for the first time as an impurity and synthesized as an individual compound, which has been characterized by X-ray diffraction, electron microscopy, chemical analysis, and photoelectron spectroscopy data; its homogeneity range has been determined, and electroconductive characteristics have been studied.     

Structure and electrical conductivity of cobalt-doped Bi<Subscript>26</Subscript>Mo<Subscript>10</Subscript>O<Subscript>69</Subscript>

The existence boundaries, structures, and transport parameters of Bi_{1 ? x} Co _x [Bi₁₂O₁₄]Mo₅O_{20 ± δ} and Bi[Bi₁₂O₁₄]Mo_{5 ? y} Co _y O_{20 ± δ} solid solutions, which have a unique columnar structure, were studied. Electrical conductivity in these solid solutions was studied by impedance spectroscopy.     

High-pressure defect phase Tm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

Perovskite-related oxide Tm _x Cu₃V₄O₁₂ (space group Im \(\bar 3\), Z = 2, a = 7.262?7.273 Å) with vacancies in the cationic sublattice has been prepared for the first time under barothermal conditions (p = 7.0?9.0 GPa, T = 900?1100°C). Electric resistivity (10–300 K) and magnetic susceptibility (0–300 K) were studied as a function of temperature. Tm _x Cu₃V₄O₁₂ is shown to have a metallic conductivity and paramagnetism.     

Phase composition,formation parameters,and morphology of precipitates in the LiVO<Subscript>4</Subscript>-VOSO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

The phase and chemical compositions of the precipitates formed in the LiVO₃-VOSO₄-H₂O system at initial pH within 1 ≤ pH ≤ 4 and 90°C were studied. The following phases were prepared: an α phase Li_1.4(VO)_1.3[H₂V₁₀O₂₈] · nH₂O and a β phase Li_{0.6 ? x} H_{1.4 + x} [V₁₂O_{31 ? y/2}] · nH₂O (0 ≤ x ≤ 0.5, 1.3 ≤ y ≤ 2.0) with a layered structure. Li_0.4V₂O₅ · H₂O nanorods with the interlayer distance 10.30 ± 0.08 Å were synthesized at 180°C in an autoclave. The morphology, IR spectra, and main formation processes for these polyvanadates were studied.     

Preparation of mesoporous Ce<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> mixed oxides and their catalytic properties in methane combustion

Mesoporous Ce_{1 ? x} Fe _x O₂ mixed oxide catalysts of different molar ratios (x = 0.1–0.5) were prepared by the citric acid sol-gel method and the microwave technique. The activities of Ce_{1 ? x} Fe _x O₂ mixed oxides on methane combustion were investigated, and the structure and reductive properties were characterized by XRD, BET, DRS, and TPR. The data showed that Ce_{1 ? x} Fe _x O₂ mixed oxides prepared were mesoporous material. When x ≤ 0.2, the transition metal Fe incorporated into the lattice of CeO₂ to form cubic Ce_{1 ? x} Fe _x O₂ solid solutions, and mixed phases of cubic Ce_{1 ? x} Fe _x O₂ solid solutions and α-Fe₂O₃ existed when x > 0.2. Ce_{1 ? x} Fe _x O₂ solid solutions show higher activity for methane combustion than pure CeO₂, especially for Ce_0.9Fe_0.1O₂.     

High-pressure defect phase Nd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

A perovskite-like oxide Nd _x Cu₃V₄O₁₂ (space group Im \(\bar 3\) Z = 2, a = 7.278–7.322 Å) with cationic vacancies was prepared for the first time under triaxial compression of p = 6.0–9.0 GPa at 700–1300°C. The compound has a metal-type conductivity, paramagnetic properties, and a phase transition.     

High-pressure defect phase La<Subscript>x</Subscript>Cu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

Perovskite-like nonstoichiometric oxide La _x Cu₃V₄O₁₂ (space group Im \(\bar 3\), Z = 2, a = 7.313–7.354 Å) with cation-site vacancies has been prepared for the first time at high pressures (p = 6.0–8.0 GPa) and high temperatures (T = 700–1100°C). The compound has metal-type conductivity and paramagnetic properties, and undergoes a phase transition.     

XPS spectra of vanadium-doped disulfides CuCrS<Subscript>2</Subscript>

The charged state of atoms in layered cation-substituted disulfides CuCr_1?x V _x S₂ (x = 0?0.4) was studied using X-ray photoelectron spectroscopy. The study was performed with polycrystalline powder and ceramic samples of chromium-copper disulfides. CuCr_1?x V _x S₂ samples were shown to comprise differently charged atoms of chromium, copper and vanadium, the charged state of which varies with the concentration of vanadium cations (x).     

Synthesis,structure, and properties of substituted bismuth niobates Bi<Subscript>3</Subscript>Nb<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Er<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>7–δ</Subscript>

Results are reported of a study of the structural and electrical characteristics of substituted bismuth niobates with composition Bi₃Nb_1–x Er _x O_7–δ, which are promising oxygen-ion conductors. The homogeneity regions of solid solutions were determined by X-ray phase analysis and electron microscopy with X-ray fluorescence microanalysis, and their crystal-chemical parameters were calculated. The electrical conductivity of sintered samples was examined by impedance spectroscopy.     

Formation of solid solutions of multiferroics in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The sequence of phases appearance during the formation of Bi_1–xNd_xFeO₃ solid solutions in powder oxides mixtures of bismuth, neodymium, and iron has been determined. It has been shown that the closeness of the reaction mixture composition to that of the individual compound (BiFeO₃ or NdFeO₃) is essential for the realization of the series of phase transformations yielding solid solutions of multiferroics Bi_1–xNd_xFeO₃ as the final product, due to the prevalence of various interphase contacts in the starting reaction zone.     

Production and characteristics of substituted lanthanum niobate LaNb<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>W<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4 + δ</Subscript>

Solid solutions LaNb_1–x W _x O_{4 + δ} (x = 0.02–0.10, Δx = 0.02) were investigated, which crystallize in the monoclinic system (space group I2/c) at room temperature and undergo a phase transition into the tetragonal modification with increasing temperature. The stability of various modifications was analyzed by high-temperature X-ray powder diffraction analysis. The electrical conductivity of sintered samples was studied by impedance spectroscopy. Insertion of tungsten into the niobium sublattice leads to an increase in the conductivity of the solid solutions.     

BIFEVOX Composites: Manufacture and Characterization

Design of composites is a way to improve the quality of solid electrolytes. By mechanically mixing and annealing substituted bismuth vanadate with nanosized aluminum, bismuth, and zirconium binary oxides, we obtained heterogeneous materials Bi₄V_1.7Fe_0.3O_{11 – δ}/xAl₂O₃, Bi₄V_1.7Fe_0.3O_{11 – δ}/xBi₂O₃, and Bi₄V_1.7Fe_0.3O_{11 – δ}/xYSZ. The investigation tools were X-ray powder diffraction and electron microscopy with energy-dispersive microanalysis. The composition of materials was studied, the non-interaction of components was elucidated in the aluminum oxide and zirconium oxide composite series, and a nonuniform distribution of nanopowder particles across the surfaces and cleaves of sinters was discovered. The bismuth atoms from bismuth oxide were shown to be capable of incorporating into the Bi₄Fe_0.3V_1.7O_{11 – δ} structure. The charge transport characteristics of the materials were studied by impedance spectroscopy. No changes were observed in logσ–10³/T trends in composites with various binary oxides and various oxide contents. An increase in binary oxide concentration was shown to give rise to an insignificant decay in electrical conductivity.     

One-dimensional oxygen-ion conductors based on phosphorus-substituted bismuth molybdates: Preparation and characterization

Our study deals with the preparation, characterization, and electric conduction properties of complex oxides of formula Bi₁₃Mo_5–xP _x O_34.5–d, which manifest oxygen-ion conductivity at medium-range temperatures.     

A study of phase formation in the subsolidus region of the system Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MnMoO<Subscript>4</Subscript>-Cr<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phase relationships in the subsolidus region of the system Na₂MoO₄-MnMoO₄-Cr₂(MoO₄)₃ were studied by means of X-ray diffraction and differential-thermal analyses. The possibility of obtaining a variablecomposition phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ (0 ≤ x ≤ 0.5) and ternary molybdate NaMn₃Cr(MoO₄)₅ was examined. The temperature dependence of the conductivity of the phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ was analyzed.