Synthesis,structure, and thermal expansion of sodium zirconium arsenate phosphates

Sodium zirconium arsenate phosphates NaZr₂(AsO₄) _x (PO₄)_3?x were synthesized by precipitation technique and studied by X-ray diffraction and IR spectroscopy. In the series of NaZr₂(AsO₄) _x (PO₄)_3?x , continuous substitution solid solutions are formed (0 ≤ x ≤ 3) with the mineral kosnarite structure. The crystal structure of NaZr₂(AsO₄)_1.5(PO₄)_1.5 was refined by full-profile analysis: space group R \(\bar 3\) c, a = 8.9600(4)Å, c = 22.9770(9) Å, V = 1597.5(1) ų, R _wp = 4.55. The thermal expansion of the arsenate-phosphate NaZr₂(AsO₄)_1.5(PO₄)_1.5 and the arsenate NaZr₂(AsO₄)₃ was studied by thermal X-ray diffraction in the temperature range of 20–800°C. The average linear thermal expansion coefficients (α_av = 2.45 × 10^?6 and 3.91 × 10^?6 K^?1, respectively) indicate that these salts are medium expansion compounds.     

New Phosphate-Sulfates with NZP Structure

NaZr_2–xB_x(PO₄)_3–2x(SO₄)_2x (0 ≤ x ≤ 1.25, B = Mg, Co, Ni, Cu, Zn), and NaZr_2–xR_x(PO₄)_3–x(SO₄)_x (0 ≤ x ≤ 1.25, R = Al, Fe) phosphate-sulfates series have been prepared by a sol–gel process. These compounds belong to the NaZr₂(PO₄)₃ (NZP) structure family and crystallize in hexagonal crystal system, space group R\(\bar 3\)c. Limited solid solution series were found to exist; their formation temperatures and thermal stability limits were determined. Particle sizes as determined by microstructure observation were 50–200 nm, and for Cu- and Zn-containing samples, 200–500 nm. The thermal expansion of phosphate-sulfate NaZr_1.25Cu_0.75(PO₄)_1.5(SO₄)_1.5 was studied in the range 25–700°C. Thermal expansion coefficients and thermal expansion anisotropy were found to be α_a =–5.40 × 10^–6 °C^–1, α_с = 18.88 × 10^–6 °C^–1, α_avg = 2.69 × 10^–6 °C^–1, and Δα = 24.28 × 10^–6 °C^–1.     

Phase formation in the Ag<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MgMoO<Subscript>4</Subscript>-Al<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> system

The subsolidus region of the Ag₂MoO₄-MgMoO₄-Al₂(MoO₄)₃ ternary salt system has been studied by X-ray phase analysis. The formation of new compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.4) and AgMg₃Al(MoO₄)₅ has been determined. The Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ variable-composition phase is related to the NASICON type structure (space group R \(\bar 3\) c). AgMg₃Al(MoO₄)₅ is isostructural to sodium magnesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group P \(\bar 1\), Z = 2) with the following unit cell parameters: a = 9.295(7) Å, b = 17.619(2) Å, c = 6.8570(7) Å, α = 87.420(9)°, β = 101.109(9)°, γ = 91.847(9)°. The compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ and AgMg₃Al(MoO₄)₅ are thermally stable up to 790 and 820°C, respectively.     

Systems Li<Subscript>2</Subscript>O(Na<Subscript>2</Subscript>O)-CdO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>: Phase composition and phase diagrams

The subsolidus phase composition of the M₂O-CdO-V₂O₅ systems with M = Li or Na is studied. Double orthovanadates MCdVO₄ and MCd₄(VO₄)₃ form solid solutions of composition Li_{1 ? 2x/3}Cd _x/3CdVO₄ (0 ≤ x ≤ 1, orthorhombic space group Cmcm, modulation at x = 0.6) and Na_{3 ? 2x} Cd_{3 + x} (VO₄)₃ (0 ≤ x ≤ 0.10 and 0.30 ≤ x ≤ 1, orthorhombic space group Cmcm and Pn2₁ a or Pnma, respectively). In the range 0.10 < x < 0.30, the end-members of the solid solutions coexist. Isothermal sections of the systems are mapped.     

Synthesis and study of solid solutions between cobalt and nickel phosphates with varied degree of anion protonation

Continuous substitutional solid solutions between cobalt and nickel phosphates with varied degree of anion protonation were obtained: Co_1?x Ni _x HPO₄·1.5H₂O and (Co_1?x Ni _x )₃(PO₄)₂·8H₂O, where 0 ≤ x ≤ 1.00. The thermolysis of the solid solutions was studied by the example of Co_1?x Ni _x HPO₄·1.5H₂O. The phases synthesized were compared with the previously described continuous solid solution Co_1?x Ni _x (H₂PO₄)₂·2H₂O.     

Synthesis of (Ni<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>P (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.65) substitution solid solution

The phosphides (Ni_{1 ? x} Co _x )₂P (0 ≤ x ≤ 0.65) crystallizing in the hexagonal system, space group P \(\bar 6\)2m, were synthesized in two steps starting from the continuous solid solution (Ni_{1 ? x} Co _x )₃(PO₄)₂ · 8H₂O. The initial phosphates were first completely dehydrated at 800°C and then reduced with hydrogen at 900–1000°C for 1–2 h.     

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.     

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).     

Isomorphic substitution of neodymium and gadolinium for calcium in synthetic hydroxovanadate

Isomorphic substitution of neodymium and gadolinium for calcium in synthetic hydroxovanadate Ca_{5 ? x} M _x (VO₄)₃(OH)_{1 ? x} O _x (M = Nd, Gd) is studied in the range 700–1000°C using X-ray powder diffraction, single-crystal X-ray diffraction (Rietveld technique), and IR spectroscopy. Single-phase solid solutions at 800°C are formed with x ≤ 0.35 for M(III) = Nd and x ≤ 0.3 for M(III) = Gd. With high x, the apatite solid solution coexists with Ca₃(VO₄)₂, Nd₂O₃, and X phases. With increasing x in the homogeneous region, the intensity of the bands of stretching vibrations and librations of OH groups decrease. Single-crystal X-ray diffraction shows that neodymium and gadolinium substitute for calcium in solid solutions mostly in Ca(2) positions.     

Specific features of La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> solid state synthesis

Investigations of solid state preparation of La_1?xMnO₃ compounds (_x = 0, 0.1, 0.14, 0.17, 0.23) has revealed a number of intermediate structural states connected with progressive ordering of crystal structures. Freshly prepared non-stoichiometric compounds (x ≠ 0) are characterized by Mn⁴⁺ inclusion (0.09 ≤ y(Mn⁴⁺) 0.24) and rhombohedral space group \(R\bar 3c\).     

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.     

Methanol transformations on framework lithium zirconium vanadate phosphates

The catalytic activity of framework phosphates of the general formula LiZr₂(VO₄)_x(PO₄)_3–x with different degrees of phosphorus replacement (x = 0, 0.1, 0.3, 0.4, 0.6, and 0.8) was studied in methanol transformations in an inert atmosphere. It was shown that the ratio between the activity and selectivity of the catalysts in dehydration and dehydrogenation reactions is determined by their vanadium content and the process temperature.     

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.     

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.     

Effects of Cr doping on the electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material for lithium ion batteries

A series of Cr-doped Li₃V_2???x Cr _x (PO₄)₃ (x?=?0, 0.1, 0.25, and 0.5) samples are prepared by a sol–gel method. The effects of Cr doping on the physical and chemical characteristics of Li₃V₂(PO₄)₃ are investigated. Compared with the XRD pattern of the undoped sample, the XRD patterns of the Cr-doped samples have no extra reflections, which indicates that Cr enters the structure of Li₃V₂(PO₄)₃. As indicated by the charge–discharge measurements, the Cr-doped Li₃V_2???x Cr _x (PO₄)₃ (x?=?0.1, 0.25, and 0.5) samples exhibit lower initial capacities than the undoped sample at the 0.2 C rate. However, both the discharge capacity and cycling performance at high rates (e.g., 1 and 2 C) are enhanced with proper amount of Cr doping (x?=?0.1). The highest discharge capacity and capacity retention at the rates of 1 and 2 C are obtained for Li₃V_1.9Cr_0.1(PO₄)₃. The improvement of the electrochemical performance can be attributed to the higher crystal stability and smaller particle size induced by Cr doping.     

Interactions in the Al<Subscript>2</Subscript>TiO<Subscript>5</Subscript>-Ti<Subscript>2</Subscript>O<Subscript>3</Subscript> System

Interactions in the Al₂TiO₅-Ti₂O₃ system were studied and the regions of existence of Al_2?2xTi _2x ³⁺ Ti⁴⁺O₅ solid solutions with a pseudobrookite structure were determined.     

Effect of Active Fillers on Properties of Heat-Resistant Composites

The effect of active fillers such as titanium nitrides TiN _x , carbides TiC _x , and carbonitrides TiC _x N _y (0.5 < x or x + y ≤ 1.0) on properties of polymeric composites based on thermostable binders PAIS-104, SFP-012 AK-30, and ED-20 is studied.     

Phase equilibria in the system LaMnO<Subscript>3</Subscript>-SrMnO<Subscript>3</Subscript>-SrCrO<Subscript>4</Subscript>-LaCrO<Subscript>3</Subscript>

A continuous solid solution LaMn_1?y Cr _y O₃ with an orthorhombic structure is found to exist in the range of 0.0 ≤ y ≤ 1.0. An orthorhombic solid solution La_1?x Sr _x CrO₃ exists in the range of 0.0 ≤ x ≤ 0.1. The stability boundaries are determined for the perovskite phase La_1?x Sr _x Mn_1?y Cr _y O₃. An isobaric-isothermal section LaMnO₃-SrMnO₃-SrCrO₄-LaCrO₃ of the system La₂O₃-SrO-Mn₃O₄-Cr₂O₃ in air at 1100°C is designed.     

Effect of the introduction procedure and concentration of yttrium cations on the crystal structure of (1–<Emphasis Type="Italic">x</Emphasis>)ZrO<Subscript>2</Subscript> · <Emphasis Type="Italic">x</Emphasis>Y<Subscript>2</Subscript>O<Subscript>3</Subscript> powders

An integrated study of the crystal and local structures of complex oxides (1–x)ZrO₂ · xY₂O₃ (x = 0.005–0.18, YSZ), precipitated from solutions of metal salts and annealed in air, was carried out. For the use of deposition from solutions, reverse co-precipitation was found to be the method of choice for introducing yttrium cations into YSZ, ensuring the maximum stabilization effect of high-temperature phases. An increase in the yttrium content induces polymorphic transformations, monoclinic phase (P21/a) → tetragonal phase (P4₂/nmc) (for x = 0.02) → cubic phase (Fm\(\bar 3\)m) (for x = 0.08), in the samples prepared at temperatures of ≤1000°C. A Raman study of the local structure of YSZ powders confirmed the formation of a single-phase tetragonal structure for the 2YSZ and 3YSZ samples and identified trace amounts of the tetragonal phase for the 8YSZ and 18YSZ samples with the cubic structure.     

Subsolidus phase relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Li<Subscript>2</Subscript>O-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> (Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>) systems

The phase composition has been studied and an equilibrium phase diagram has been designed for the Al₂O₃-Li₂O-R₂O₅ (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li₂O. New phases with the composition Li_1+x Al_1?x O_2?x , where x = 0–0.67, have been found.