Phase formation in the Ag3PO4-ScPO4 quasi-binary system

The phase formation in the subsolidus region of the Ag₃PO₄-ScPO₄ quasi-binary system was studied by X-ray powder diffraction and differential thermal analyses throughout the range of concentration ratios of the initial components at an interval of 10 mol % within the temperature range 20–1000°C in air at atmospheric pressure. A T-x section was constructed. The formation of the binary phosphate Ag₃Sc₂(PO₄)₃ melting incongruently at 1300 ± 5°C was detected. The composition of an eutectic (with the melting point 900 ± 5°C) is between those of the compounds Ag₃PO₄ and Ag₃Sc₂(PO₄)₃.     

Ionic conductivity of double vanadate Ag3Sc2(VO4)3

Ionic conductivity of double vanadate Ag₃Sc₂(VO₄)₃ with the NASICON structure is studied by the method of impedance spectroscopy in the frequency range from 5 to 5 × 10⁵ Hz and in the temperature range of 300–827 K. The vanadate Ag₃Sc₂(VO₄)₃ is prepared in the form of fine crystalline powder by solid-state synthesis from V₂O₅, Sc₂O₃, and AgNO₃ at 1173 K. The conductivity of Ag₃Sc₂(VO₄)₃ ceramic samples σ = 8 × 10^?3 S/cm (at 563 K). The σ vs. T curve demonstrates an anomaly at 563–623 K which corresponds to thermal effects in this temperature range. The values of enthalpy of ion transport activation are ΔH = 0.40 ± 0.05 eV (T < 563 K) and ΔH = 0.30 ± 0.05 eV (T > 623 K). The ionic conductivity of Ag₃Sc₂(VO₄)₃ is due to Ag⁺ ions localized in channels of the framework structure of the NASICON type.     

New complex silver-scandium vanadates

New complex silver-scandium vanadates, Ag₃Sc(VO₄)₂, AgBaSc(VO₄)₂, and Ag₃Sc₂(VO₄)₃, were synthesized, and their crystallographic parameters were determined. The products synthesized by different methods were studied by X-ray powder diffraction, electron-probe X-ray microanalysis, and ESR. Based on these data, the synthetic procedures were optimized. The thermal properties of complex vanadates were studied by DTA. The compounds AgBaSc(VO₄)₂ and Ag₃Sc₂(VO₄)₃ were shown to exhibit polymorphism. The compounds Ag₃Sc(VO₄)₂, AgBaSc(VO₄)₂, and Ag₃Sc₂(VO₄)₃ decompose at 760, 780, and 960 °C. respectively.     

Phase formation in the Ag2MoO4-CoMoO4-Al2(MoO4)3 system

The subsolidus region of the Ag₂MoO₄-CoMoO₄-Al₂(MoO₄)₃ ternary salt system was studied by X-ray powder diffraction analysis. New compounds Ag_1?x Co_1?x Al_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.4) and AgCo₃Al(MoO₄)₅ were detected to form. The variable-composition phase Ag_1?x Co_1?x Al_{1 + x} (MoO₄)₃ is of the NASICON structure type (space group \(R\bar 3c\) ). AgCo₃Al(MoO₄)₅ crystallizes in the triclinic symmetry (space group \(P\bar 1\) Z = 2) with the unit cell parameters a = 6.9101(6), b = 17.519(1), c = 6.8241(6) Å, α = 87.356(7)°, β = 101.078(7)°, and γ = 91.985(9)°. The compounds are thermally stable until 770–780 and 760°C, respectively.     

Phase formation in the Ag2O-ZnO (CdO)-V2O5 systems

The phase composition of the Ag₂O-ZnO(CdO)-V₂O₅ systems has been studied. Two new orthovanadates have been synthesized: AgZnVO₄ (monoclinic space group P21/n, a = 5.68710, b = 12.54080, c = 5.65947 Å, β = 116.209°) and AgCd₄(VO₄)₃ (orthorhombic space group Pnma, a = 9.82438 b = 7.01250, c = 5.37393 Å). One double metavanadate Ag₂Cd(VO₃)₄ has been synthesized. A continuous solid solution formulated as Ag_{3 ? 2x} Cd_{3 + x} (VO₄)₃ has been found to exist between AgCd₄(VO₄)₃ and already described AgCdVO₄. The Ag₂O-ZnO (CdO)-V₂O₅ systems have been triangulated in the subsolidus region.     

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.     

High-temperature heat capacity and thermodynamic properties of pyrovanadate Pb<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> and orthovanadate Pb<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The heat capacities of Pb₂V₂O₇ and Pb₃(VO₄)₂ as a function of temperature in the range 350–965 K have been studied by the differential scanning calorimetry method. The C_P = f(T) curve for Pb₂V₂O₇ is described by the equation C_p = (230.76 ± 0.51) + (73.60 ± 0.50)×10^-3T ? (18.38 ± 0.54)×10⁵T^-2 in the entire temperature range. For Pb₃(VO₄)₂, there is a well-pronounced extreme point in the C_P = f(T) curve at T = 371.5 K, which is caused by the existence of a structural phase transition. The thermodynamic properties of the oxide compounds have been calculated.     

Phase equilibria in the Ag4SSe–As2Se3 system

The phase diagram of the system Ag₄SSe–As₂Se₃ is studied by means of X-ray diffraction, differential thermal analyses and measurements of the microhardness and the density of the materials. The unit-cell parameters of the intermediate phases 3Ag₄SSe·As₂Se₃ (phase A) and Ag₄SSe·2As₂Se₃ (phase B) are determined as follows for phase A: a=4.495 Å, b=3.990 Å, c=4.042 Å, α=89.05°, β=108.98°, γ=92.93°; for phase B: a=4.463 Å, b=4.136 Å, c=3.752 Å, α=118.60°, β=104.46°, γ=83.14°. The phase 3Ag₄SSe·As₂Se₃ and Ag₄SSe·2As₂Se₃ have a polymorphic transition α?β consequently at 105 and 120°C. The phase A melts incongruently at 390°C and phase B congruently at the same temperature.     

Phase formation in the system involving silver, magnesium, and indium molybdates

The subsolidus region of the Ag₂MoO₄-MgMoO₄-In₂(MoO₄)₃ ternary salt system has been studied by X-ray powder diffraction. The formation of new compounds Ag_{1 ? x} Mg_{1 ? x} In_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.6) and AgMg₃In(MoO₄)₅ has been established. The unit cell parameters of solid-solution samples have been determined. The Ag_{1 ? x} Mg_{1 ? x} In_{1 + x} (MoO₄)₃ phase of variable composition has a NASICON-type structure (space group R $ \bar 3 $ c) AgMg₃In(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 = 7.0374(5) Å, b = 17.932(1) Å, c = 6.9822(4) Å, α = 87.309(6)°, β = 100.832(6)°, γ = 92.358(6)°. The compounds Ag_{1 ? x} Mg_{1 ? x} In_{1 + x} (MoO₄)₃ and AgMg3In(MoO₄)₅ are thermally stable up to 960 and 1030°C, respectively.     

Phase equilibria in the CdAs<Subscript>2</Subscript>–Cd<Subscript>3</Subscript>As<Subscript>2</Subscript>–MnAs ternary system

We determined, using a set of physicochemical methods, including X-ray powder diffraction (XRD), differential thermal analysis, and microstructure studies, that the CdAs₂–Cd₃As₂–MnAs ternary system is bounded by three eutectic-type quasi-binary sections: Cd₃As₂–MnAs, CdAs₂–MnAs, and Cd₃As₂–CdAs₂. For Cd₃As₂–MnAs and CdAs₂–MnAs sections, the eutectic coordinates are, respectively, 75 mol % Cd₃As₂ + 25 mol % MnAs, T _m.eut = 604°C; and 92 mol % CdAs₂ + 8 mol % MnAs, T _m.eut = 608°C. These are rod eutectics. Manganese solubilities in Cd₃As₂ and CdAs₂ phases are insignificant and, according to XRD and SEM, they do not exceed 1 at %. The binary eutectics of the quasi-binary sections form ternary eutectic Cd₃As₂ + CdAs₂ + MnAs, whose average composition as probed by SEM is 34.5 at % Cd, 63 at % Cd and 2.5 at % As and T _m.eut = 600°C. Cadmium and manganese arsenide alloys are ferromagnets with the Curie point at ~320 K. The magnetic and electric properties are due to ferromagnetic MnAs microinclusions.     

The phase diagram of the system La2(SO4)3Ag2SO4

The phase diagram of the system La₂(SO₄)₃Ag₂SO₄ was studied by DTA, XRD, SEM, and optical methods. One double salt is formed at 67 mole% La₂(SO₄)₃ and this melts incongruently at 876±6°C. A eutectic is formed at 8 mole% La₂(SO₄)₃ and at a temperature of 618±3°C. Suppression of decomposition was effected by the sealed tube method, but some reference is made to experiments conducted with a flowing atmosphere of SO₃, SO₂ and O₂.     

Stable tetrahedron of lithium bromide,metavanadate, and molybdate and potassium bromide in the Li,K || Br,VO<Subscript>3</Subscript>, MoO<Subscript>4</Subscript> quaternary reciprocal System

Phase equilibria in the LiBr–LiVO₃–Li₂MoO₄–KBr quaternary system (the stable tetrahedron of the quaternary reciprocal system Li, K || Br, VO₃, MoO₄) were studied by differential thermal analysis. The composition and melting point of a quaternary eutectic were determined: 56.7 mol % LiBr, 1.5 mol % LiVO₃, 4.9 mol % Li₂MoO₄, 36.9 mol % KBr, 321°C.     

Synthesis of Sb(VO3)3 and study of ternary system xNH4VO3?+?(1???x)(NH4)2HPO4?+?Sb2O3

Sb(VO₃)₃ has been synthesized by interaction between NH₄VO₃ and Sb₂O_3. The compound crystallizes in monoclinic system with lattice parameters: a = 17.150; b = 15.940; c = 14.600 Å and angle ?? = 90.50°. The scanning electronic microscopy shows thin flat plates measuring ~20 ??m along with detritus material. The synthesis was simulated by thermal analysis and the final product identified by X-ray diffraction. Thermal analyses of the ternary system xNH₄VO₃ + (1 ? x)(NH₄)₂HPO₄ + Sb₂O₃ lead to the formation of Sb(VO₃)₃ and SbPO₄ at 500 °C. At high temperature (900 °C), SbVO₄, SbOPO₄, VO and SbP₅O₁₄ are formed. The data of thermal analysis match with the composition of intermediate and final products. No solid solutions containing simultaneously PO ₄ ^?3 and VO ₄ ^?3 ions have been found.     

Preparation and studies of a new ammonium vanadium bronze, (NH4)xV2O5

A new bronze-type phase of composition (NH₄)_0.40±0.02V₂O₅ is obtained around 230°C during the thermal decomposition of NH₄VO₃ in hydrogen atmosphere. The bronze intermediate is characterized by X-ray diffraction, electrical conductivity, magnetic susceptibility, and ESR studies. It is found to be isostructural with other known β-type vanadium bronzes of general formula M_xV₂O₅, where M is usually a monovalent metal. Electrical conductivity and magnetic studies indicate the localized character of conduction electrons at V⁺⁴ sites. At high temperatures (>400°C), the bronze undergoes decomposition and subsequent reduction to V₂O₃ in hydrogen atmosphere.     

Subsolidus phase diagrams of the systems Cs2MoO4-R2(MoO4)3-Zr(MoO4)2, where R = Al, Sc, or In

The systems Cs₂MoO₄?R₂(MoO₄)₃?Zr(MoO₄)₂, where R = Al, Sc, or In, have been investigated in the subsolidus region by X-ray powder diffraction. Quasi-binary joins have been revealed, and triangulation has been carried out. Six new triple molybdates have been prepared with the component ratio equal to 1 : 1 : 1 (mol/mol) (S ₁) and 5 : 1 : 2 (S ₂). The crystal parameters for the 5 : 1 : 2 compounds have been determined, and the electrical properties of the 1 : 1 : 1 compounds have been investigated.     

Heat capacity and thermodynamic functions of MnBr2 · 4D2O and MnCl2 · 4D2O

The heat capacities of MnBr₂ · 4D₂O and MnCl₂ · 4D₂O have been experimentally determined from 1.4 to 300 K. The smoothed heat capacity and thermodynamic functions (H°_TH°₀) and S°_T are reported for the two compounds over the temperature range 10 to 300 K. The error in the thermodynamic functions at 10 K is estimated to be 3%. Additional error in the tabulated values arising from the heat capacity data above 10 K is thought to be less than 1%. A λ-shaped heat capacity anomaly was observed for MnCl₂ · 4D₂O at 48 K. The entropy associated with the anomaly is 1.2 ± 0.2 J/mole K.     

Synthesis and characterization of LiCo3/5Mn2/5VO4 ceramics

Dielectric and a.c. conductivity properties of LiCo_3/5Mn_2/5VO₄ ceramic are investigated. This compound is prepared by solution-based chemical method and the formation is checked by X-ray diffraction (XRD) study. XRD analysis at room temperature shows an orthorhombic phase. Frequency dependence of dielectric constant (?_r) at different temperatures shows a dispersive behavior at low frequencies. Temperature dependence of ?_r at different frequencies indicates the transition temperature (T_c) = 235 °C, 245 °C, 257 °C and 265 °C with (?_r)_max. ～3689, 1373, 750 and 386 for 10, 50, 100 and 200 kHz respectively. A.c. conductivity analysis indicates that electrical conduction in the material is a thermally activated process.     

Phase equilibria in the Ag2Te-ZnTe and Ag2Te-Zn systems

The state diagrams (T-x) of the systems Ag₂Te-ZnTe(I) and Ag₂Te-Zn(II) are offered on the ground of data obtained by differential thermal analysis, X-ray phase analysis, microstructural analysis and measurements of the density and the microhardness of samples synthesized. The systems studied are quasibinary sections of the ternary system Ag-Zn-Te. System I is characterized by two eutectic and three eutectoidal non-variant equilibria as well as by an intermediate compound Ag₂ZnTe₂, which melts congruently at 880°C. The latter exists in the range from 120 to 880°C in two polymorphic modifications (T_ʅ→β=515°C). System II is characterized by one eutectic, two eutectoidal and one peritectic nonvariant equilibria, boundary solid solutions on the ground of Ag₂Te and Zn and one intermediate phase of the composition Ag₄Zn₃Te₂, which melts congruently at 880°C.     

Phase equilibria in the V2O5-NaVO3-Ca(VO3)2-Mn2V2O7 system and interactions of phases with H2SO4 and NaOH solutions

Phase composition of the V₂O₅-NaVO₃-Ca(VO₃)₂-Mn₂V₂O₇ system was studied, and a subsolidus phase diagram constructed. The tetrahedration of the diagram is determined by the fact that the end-member of Ca_1–x Mn _x (VO₃)₂ solid solution is in equilibrium with all compounds of the system (V₂O₅, NaVO₃, Ca(VO₃)₂), vanadium β-bronzes Na _x V₂O₅ (0.22 ≤ x ≤ 0.40) and κ-bronzes (0.25 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.16), Mn₂V₂O₇, and Na₂Mn₃(V₂O₇)₂ and with the end-members of reciprocal solid solutions based on calcium and sodium metavanadates. At 20°C, the degree of vanadium dissolution α for Na₂Ca(VO₃)₄ is 100% for 0.5 ≤ pH ≤ 10; for the other phases of the system, vanadium dissolution ranges from 100 to 10% for pH below 3.5; in the alkaline pH range, ≤ 10%. Sodium for calcium substitution in Ca(VO₃)₂ increases α in aqueous NaOH to 20%. For Na₂Mn₃(V₂O₇)₂, α decreases from 92 to 80% as pH changes from 0.5 to 2.5; at pH above 4, α = 30%.     

Hexametavanadates M<Stack><Subscript>4</Subscript><Superscript>+</Superscript></Stack>M<Superscript>2+</Superscript>(VO<Subscript>3</Subscript>)<Subscript>6</Subscript>: Thermal stability and luminescent characteristics

Rhombohedral hexametavanadates K₄Sr(VO₃)₆, K₄Ba(VO₃)₆, Rb₄ Ba(VO₃)₆, and Cs₄Ba(VO₃)₆ melt incongruently in the temperature range of 491 to 600°C. Cooling of peritectic melts yields mixtures of compounds typical of M₂⁺O-M²⁺O-V₂O₅ systems, far from equilibrium and depending on the cooling kinetics. The vanadate Cs₄Ba(VO₃)₆ undergoes reversible polymorphic transformation at 360°C. All compounds show broad-band luminescence with a maximum of the luminescence spectrum at 490–590 nm with three types of excitation. The vanadates K₄Sr(VO₃)₆ and Rb₄Ba(VO₃)₆ show the highest luminescence intensity at room temperature. The latter is also most efficient at liquid nitrogen temperatures. The luminescence spectra depend on the excitation of vanadates. Three hypotheses were put forward to interpret this finding. The nature of luminescence is attributed to the relaxation of electronic excitation in [VO₄]³⁻ structural tetrahedra present in the vanadates. The performance characteristics of luminophores were determined. These luminophores may be promising as X-ray luminescent screens, radioluminescence indicators, and light-emitting diode devices.