Phase equilibria in the Tl-TlCl-Te system and thermodynamic properties of the compound Tl<Subscript>5</Subscript>Te<Subscript>2</Subscript>Cl

The Tl-Te-Cl system was studied in the Tl-TlCl-Te composition region by differential thermal analysis, X-ray powder diffraction, and emf and microhardness measurements. A series of polythermal sections, an isothermal section at 400 K, and a projection of the liquidus surface of the phase diagram were constructed. The ternary compound Tl₅Te₂Cl characterized by a wide homogeneity region and incongruent melting by a syntectic reaction at 708 K was shown to exist. This compound was found to crystallize in tetragonal lattice (space group I4/mcm) with the parameters a = 8.921 Å, c = 12.692 Å, Z = 4. Wide phase separation regions were also found in the system, including a three-phase separation region in the Tl-TlCl-Tl₂Te subsystem. Regions of primary crystallization of phases, and the types and coordinates of in- and monovariant equilibria in the T-x-y diagram were determined. From emf measurement data, the standard thermodynamic functions of formation and the standard entropy were calculated for the compound Tl₅Te₂Cl, as follows: ?ΔG ₂₉₈ ⁰ = 355.9 ± 1.1 kJ/mol, ?ΔH ₂₉₈ ⁰ = 377.1 ± 5.0 kJ/mol, and S ₂₉₈ ⁰ = 474.1 ± 6.8 J/(mol K).     

Crystal Structure of Tl<Subscript>2</Subscript>[NbCl<Subscript>6</Subscript>] and Tl<Subscript>2</Subscript>[NbBr<Subscript>6</Subscript>]

Single crystals of Tl₂[NbCl₆] (1) and Tl₂ [NbBr₆] (2) are obtained as black needles on heating TlCl, Nb, S₂Cl₂ (1) and Tl, Nb, and Br₂ at 400°C (2). Tl₂NbBr₆ also forms in the reaction of TlBr, Nb, Br₂, and S at 500°C. Both compounds crystallize in the K₂[PtCl₆] structure type to form non-distorted octahedral [NbХ₆]^2– anions (Nb–Cl 2.397(4) Å and Nb–Br 2.516(2) Å). The magnetic properties of Tl₂[NbBr₆] in a range 5-300 K indicate an antiferromagnetic interaction between Nb⁴⁺ ion spins (d¹, S = 1/2). On cooling, the compound becomes a noncollinear ferromagnet with T_c = 23 K.     

Phase diagram of the system NaF-SnF<Subscript>2</Subscript>

The phase diagram of the binary system NaF-SnF2 was determined by using the thermal analysis method. In addition to the crystallisation fields of pure components the formation of three other crystallisation fields was observed and these were attributed to the compounds: NaF·2SnF₂, NaF·SnF₂ and 2NaF·SnF₂. The coordinates of the four eutectic points are: e ₁: 70 mol% NaF, 30 mol% SnF₂ and 255°C e ₂: 58 mol% NaF, 42 mol% SnF₂ and 238°C e ₃: 44 mol% NaF, 56 mol% SnF₂ and 246°C e ₄: 18 mol% NaF, 82 mol% SnF₂ and 191°C The model independent on the real structure of the melt was applied for the calculation of phase diagram comprising the calculation of excess molar Gibbs energy of mixing. The probable inaccuracy in the calculated phase diagram is σ=2.0°C. XRD analysis of solidified mixtures was performed in order to confirm the formation of expected compounds.     

Interaction of components in the Tl<Subscript>2</Subscript>Se-Tl<Subscript>4</Subscript>SnSe<Subscript>4</Subscript>-Tl<Subscript>9</Subscript>SbSe<Subscript>6</Subscript> quasi-ternary system

The interaction in the Tl₂Se-Tl₄SnSe₄-Tl₉SbSe₆ quasi-ternary system was studied by differential thermal analysis, X-ray powder diffraction analysis, and mathematical modeling. The projection of the liquidus surface and a spatial phase diagram of the system were constructed. It was determined that this system is of the eutectic type with boundary solid solutions based on the initial components. No formation of new intermediate compounds in the quasi-ternary system was detected.     

Quasi-ternary system Tl<Subscript>2</Subscript>Se-AgTlSe-TlBiSe<Subscript>2</Subscript>

The quasi-ternary system Tl₂Se-AgTlSe-TlBiSe (A) has been investigated by DTA, X-ray powder diffraction, microstructural analysis, and microhardness measurements. Polythermal sections AgTlSe-TlBiSe₂, AgTlSe-Tl₉BiSe₆, [Ag_0.5Tl_1.5Se]-TlBiSe₂, Tl₂Se-AgBiSe₂ (0–50 mol % AgBiSe₂), an isothermal section at 500 K, and the projection of the liquidus surface of system A have been constructed. It has been shown that the quasi-binary join AgTlSe-Tl₉BiSe₆ divides system A into two subordinate triangles, namely, Tl₂Se-Tl₉BiSe₆-AgTlSe (B) and AgTlSe-Tl₉BiSe₆-TlBiSe₂ (C). The phase diagram of subsystem B involves a univariant eutectic equilibrium while subsystem C involves an invariant eutectic equilibrium. The ternary eutectic has the coordinates 650 K, 10 mol % TlBiSe₂, and 61 mol % AgTlSe. A continuous series of solid solutions (0–12 mol % AgTlSe) has been found along the Tl₂Se-Tl₉BiSe₆ bordering system. The homogeneity region of TlBiSe₂ extends to 5 mol %.     

Phase equilibria in the PbSe-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript>-Se system and thermodynamic properties of intermediate phases

The Pb-Bi-Se system in the PbSe-Bi₂Se₃-Se-Se composition region was studied by measurement of concentration circuits of the type (−) PbSe(solid) liquid electrolyte, Pb²⁺(Pb-Bi-Se)(solid) (+) in the temperature range 300–430 K and by X-ray powder diffraction. A solid-phase equilibrium diagram was constructed, and the formation was confirmed for the ternary compounds Pb₅Bi₆Se₁₄, Pb₅Bi₁₂Se₂₃, and Pb₅Bi₁₈Se₃₂, which belong to the homologous series [(PbSe)₅] _m · [(Bi₂Se₃)₃] _n . From the emf versus temperature equations, the partial thermodynamic functions [`(DG)]\overline {\Delta G}, [`(DH)]\overline {\Delta H}, [`(DS)]\overline {\Delta S} of PbSe in alloys were calculated. Based on the solid-phase equilibrium diagram from these partial molar quantities using the corresponding data for PbSe and Bi₂Se₃, the standard thermodynamic functions of formation and standard entropies of the above ternary compounds were calculated.     

Phase equilibria and isomorphism in the LiVWO<Subscript>6</Subscript>-NaVWO<Subscript>6</Subscript> system

Compounds of composition Li _x Na_{1 − x} VWO₆ (0 ≤ x ≤ 1), which are synthetic analogues of brannerite-type minerals, were produced for the first time by solid-state synthesis at high temperatures. The structure of the compounds and their unlimited miscibility in the solid phase in the LiVWO₆-NaVWO₆ binary system were determined by X-ray diffraction. The phase equilibrium diagram was studied by differential thermal analysis together with thermodynamic modeling. It was found that the system under investigation is described by the regular solid solutions model.     

Phase diagram of the system KF-K<Subscript>2</Subscript>TaF<Subscript>7</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>

As an asymmetric organic molecular crystal, p-N,N-dimethylaminobenzaldehyde (DAB) exhibits peculiar optical property. It was first grown by solution technique adopting slow evaporation method at room temperature using CCl₄ as growth medium. The solubility of DAB increases with temperature. Good quality transparent crystals of p-N,N-dimethylaminobenzaldehyde were carefully collected and subjected various characterization studies such as UV, FTIR, ¹H and ¹³CNMR spectral studies and thermal (TG-DTG) studies to determine the purity and application oriented properties of the grown crystals.     

Phase diagram of V<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript>-Ag<Subscript>2</Subscript>O system

The results concerning the synthesis, structure and thermal properties of V₂O₅-MoO₃-Ag₂O samples in the vanadium rich region of ternary system are presented in the form of quasi-binary phase diagrams in which at constant V₂O₅/MoO₃ molar ratios, equal 9:1, 7:3 and 1:1, the content of Ag₂O was variable. A new ternary phase isostructural with NaVMoO₆ has been detected in the investigated system.     

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.     

Phase equilibria in the NaCl-NaBr-Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript> system

The binary systems NaBr-Na₂MoO₄ and NaBr-Na₃ClMoO₄ and the ternary system NaCl-NaBr-Na₂MoO₄ have been studied using physicochemical methods (DTA and powder X-ray diffraction). The compositions, melting points, and heats of phase transitions have been determined for three invariant points. The liquidus surface of the ternary system consists of the fields of sodium molybdate, Na₃ClMoO₄, and sodium chloride and bromide solid solutions. The eutectics melt at 531, 612, and 524°C; the respective heats of phase transitions are 149.27, 167.55, and 215.38 J/g.     

Phase formation in the InPO<Subscript>4</Subscript>-Na<Subscript>3</Subscript>PO<Subscript>4</Subscript>-Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> ternary system

The 950°C isothermal section of the InPO₄-Na₃PO₄-Li₃PO₄ ternary system was studied and constructed; one-, two, and three-phase fields are outlined. Five solid-solution regions exist in the system: solid solutions based on the complex phosphate LiNa₅(PO₄)₂ (olympite structure), the indium ion stabilized high-temperature Na₃PO₄ phase (Na_{3(1 − x)}In _x (PO₄); space group Fm [`3]\bar 3 m), the complex phosphate Na₃In₂(PO₄)₃, and the α and β phases of the compound Li₃In₂(PO₄)₃. A narrow region of melt was found in the vicinity of eutectic equilibria. All the phases detected in the system are derivatives of phases existing in the binary subsystems. Isovalent substitution of lithium for sodium in Na₃In₂(PO₄)₃ leads to a significant increase in the region of a NASICON-like solid solution.     

Crystal structure of Tl<Subscript>5</Subscript>{[Nb<Subscript>2</Subscript>S<Subscript>4</Subscript>Br<Subscript>8</Subscript>]Br}

By the high-temperature reaction of Nb₂S₄Br₄ and TlBr a thallium salt of the anionic cluster complex [Nb₂S₄Br₈]^4? is obtained. Its crystal structure is determined by X-ray structural analysis. The complex is also characterized by Raman spectroscopy and electrospray-mass-spectrometry.     

Surface and bulk conduction and thermodynamic properties of ionic salt CsH<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Transport properties of ionic salt CsH₅(PO₄)₂ are studied by the impedance method. The salt’s bulk conductivity ranges from 10^?8 to 10^?4 S cm^?1 in the temperature interval 90 to 145°C. The apparent activation energy is high (1.6–2.0 eV). The conductivity is slightly anisotropic: it is maximum in the [001] direction and minimum in the [100] direction (～5.6 and 1 times × 10^?6 S cm^?1, respectively, at 130°C). The conductivity of polycrystalline samples is higher by 1–2 orders of magnitude, and the activation energy drops to 1.05 eV due to the formation of a pseudoliquid layer with a high proton mobility at the intercrystallite boundary. The salt’s thermodynamic properties are examined by differential scanning calorimetry and thermogravimetry. No phase transitions are discovered in the salt up to the melting point (151.6°C), with the melting enthalpy equal to ～34 kJ mol^?1. The crystallization occurs at lower temperatures (107°C) and the crystallization enthalpy (?18 kJ mol^?1) is lower than the melting enthalpy. The melting is accompanied by slow decomposition of the salt. Factors affecting the proton transport in the salt are analyzed.     

Isomorphism in the KTaWO<Subscript>6</Subscript>-RbTaWO<Subscript>6</Subscript>-CsTaWO<Subscript>6</Subscript> system

Synthetic procedures have been developed and compounds of composition K _x Rb _y Cs _z TaWO₆ (x + y + z = 1) have been obtained. Their structure has been investigated by X-ray diffractometry. It has been shown that a continuous series of solid solutions is formed in the ternary system under study. Thermal decomposition of A^ITaWO₆ compounds (A^I = K, Rb, Cs) has been investigated by high-temperature X-ray diffractometry.     

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.     

Subsolidus phase diagrams for the Tl<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-Ln<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>-Hf(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> systems,where Ln = La-Lu

The Tl₂MoO₄-Ln₂(MoO₄)₃-Hf(MoO₄)₂ systems where Ln = La-Lu were studied in the subsolidus region using X-ray powder diffraction. Quasi-binary joins were revealed, and triangulation carried out. New ternary molybdates were prepared: Tl₅LnHf(MoO₄)₆ (5: 1: 2) for Ln = Ce-Ho, Tl₅LnHf(MoO₄)₆ (5: 1: 2) for Ln = Er-Lu, TlLnHf_0.5(MoO₄)₃ (1: 1: 1) for Ln = Ce-Nd, and Tl₂LnHf₂(MoO₄)_6.5 (2: 1: 4) for Ln = Ce-Lu. The crystallographic parameters of Tl₅LnHf(MoO₄)₆ (5: 1: 2) compounds for Ln = Er-Lu were determined.     

Ion state of atoms and the properties of perovskite-like compound CaCu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

The binding energies and valence state of atoms in the perovskite-like compound CaCu₃V₄O₁₂ have been determined using XPS spectroscopy. The stoichiometry of this phase is formulated as Ca²⁺Cu²⁺Cu ₂ ⁺ (V ₂ ⁵⁺ V ₂ ⁴⁺ O₁₂). Under an air atmosphere, the phase interacts with water vapor and oxygen. As a result, Ca(OH)₂ is formed on its surface, the Cu⁺ and V⁴⁺ ion concentrations decrease, and the Cu²⁺ and V⁵⁺ concentrations increase in association. Raman spectra show shortened cation-anion bond lengths and cation-anion-cation bond angles in CaCu₃V₄O₁₂ compared to perovskite CuVO₃; the two structures are alike. The electrical conductivity, magnetic susceptibility, thermal and sensor properties of CaCu₃V₄O₁₂ in aqueous salt solutions have been studied.     

High-temperature heat capacity and thermodynamic properties of Pb<Subscript>4</Subscript>V<Subscript>2</Subscript>O<Subscript>9</Subscript> and Pb<Subscript>8</Subscript>V<Subscript>2</Subscript>O<Subscript>13</Subscript>

The molar heat capacity of Pb₄V₂O₉ and Pb₈V₂O₁₃ in the temperature range 350–1000 K was measured by differential scanning calorimetry. It was determined that the plot C_p = f(T) for Pb₈V₂O₁₃ has an extremum within the range 416–516 K, which is due to a phase transition. A correlation was found between the heat capacity and composition of oxides in the PbO–V₂O₅ system. The data obtained allowed one to predict the specific heat capacity value for Pb(VO₃)₂.