Phase diagram of the Tl-TlI-S system and thermodynamic properties of the compound Tl<Subscript>6</Subscript>SI<Subscript>4</Subscript>

Phase equilibria in the Tl-TlI-S composition region of the Tl-S-I system were studied by differential thermal analysis, x-ray powder diffraction, and measurements of the microhardness and the emf of concentration circuits relative to a thallium electrode. A series of polythermal sections, an isothermal section at 300 K, and a projection of the liquidus surface were constructed. Primary crystallization regions of six phases, including the ternary compounds Tl₆SI₄ and Tl₃SI, were outlined, and the types and coordinates of non- and monovariant equilibria were determined. It was shown that the ternary compound Tl₆SI₄ forms tie lines with Tl, TlI, Tl₂S, Tl₄S₃, and TlS in the subsolidus region and that the homogeneity region of Tl₆SI₄ below 400 K does not exceed 1 mol %. From the emf measurement data, the standard thermodynamic functions of formation and standard entropy of the compound Tl₆SI₄ were calculated: G _f,298⁰ = −601.7 ± 2.5 kJ/mol, ΔH _f,298⁰= −595.1 ± 4.0 kJ/mol, and S ₂₉₈⁰ = 672 ± 10 J/(mol K).     

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 in the K<Subscript>2</Subscript>O-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Phase equilibria in the potassium oxide-niobium oxide system were studied by oscillation phase-analysis and thermal analysis on 35 samples with compositions lying the range from 24.9 to 66.4 mol % Nb₂O₅. The melting temperatures and melting types of the compounds of the system were refined. The composition of crystallizing phases was shown to depend on the thermal history of the sample.     

Phase equilibria in the system NaF-MgF<Subscript>2</Subscript>-SrF<Subscript>2</Subscript>

The liquidus surface of the system of sodium, magnesium, and strontium fluorides has been studied by differential thermal analysis (DTA) and visual polythermal analysis (VPA). As a result, the crystallization path has been constructed, two-and three-component nonvariant alloys have been characterized, and the fields of the components have been outlined.     

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 %.     

Projection of the liquidus surface of the Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Gd<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> system

Phase equilibria in the Sb₂Te₃-Gd₂Te₃-Bi₂Te₃ ternary system have been studied using differential thermal analysis, namely, X-ray powder diffraction, microstructure examination, thermodynamic analysis, and microhardness and alloy density measurements. Phase diagrams of some polythermal joins and liquidus surface have been constructed. The regions of primary crystallization of phases and the coordinates of all invariant and univariant equilibria in the system under investigation have been established.     

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.     

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 equilibria in the CdI<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The phase diagram of the system CdI₂-Bi₂O₃ is studied by means of X-ray diffraction, differential thermal analysis and measurements of the density of the material. As a result of the synthetic and peritectic interactions, two incongruently melting intermediate phases i.e. phase A — CdI₂·2Bi₂O₃ and phase B — CdI₂·4Bi₂O₃ (stable in the temperature interval 370–850°C) are formed.The phase A exists in two polymorphic forms with a temperature of the phase transition T =320–370°C. The unit cell parameters at low temperature modification of -CdI₂°2Bi₂O₃ were determined. (a=1.032 nm, b=1.046 nm, c=1.046 nm, =115.02°, =109.11° and =82.04°). The phases A and B have fields of homogeneity.The authors acknowledge thankfully the financial support for this work from the Ministry of Education and Science (Fond Scientific investigations — contract TN-1102).     

Phase equilibria in the system Li<Subscript>2</Subscript>O-MgO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The subsolidus region of the Li₂O-MgO-B₂O₃ system has been studied by X-ray powder diffraction and differential thermal analysis. Isothermal sections at 500–550 and 650–700°C have been designed. The following complex borates have been found to form: at 500–550°C, Li₂MgB₂O₅ and LiMgBO₃ are formed; at 650–700°C, a new phase Li₄MgB₂O₅ is formed along with LiMgBO₃; and at 5500–600°, Li₂MgB₂O₅ is formed.     

Phase equilibria in the system CaO-CoO-Co<Subscript>2</Subscript>O<Subscript>3</Subscript>-MnO-MnO<Subscript>2</Subscript>

Phase equilibria in the system CaO-CoO-Co₂O₃-MnO-MnO₂ at 700–1200°C in air were studied on the basis of published data and proper experiments. No new compounds were found. The results are presented in the form of 13 isothermal sections of the phase diagram.     

Phase equilibria in the BaS-Cu<Subscript>2</Subscript>S-Gd<Subscript>2</Subscript>S<Subscript>3</Subscript> system

Phase equilibria in the BaS-Cu₂S-Gd₂S₃ system have been studied along the 800 K isothermal section and the CuGdS₂-BaS, Cu₂S-BaGdCuS₃, BaGdCuS₃-Gd₂S₃, and BaGdCuS₃-BaGd₂S₄ polythermal sections. Complex sulfide BaGdCuS₃ is formed in the title system; it has an orthorhombic KZrCuSe₃-type structure (space group Cmcm) with the unit cell parameters equal to a = 0.40529(2) nm, b = 1.34831(6) nm, c = 1.02940(5) nm. This sulfide melts congruently at 1685 K. BaGdCuS₃ is in equilibrium with sulfides Cu₂S, BaS, Gd₂S₃, CuGdS₂, BaGd₂S₄, BaCu₄S₃, and BaCu₂S₂ and with compositions in the C₀ solid-solution region of the Cu₂S-Gd₂S₃ system. Eutectics are formed between compounds CuGdS₂ and BaGdCuS₃ at 7.0 mol % BaS and T = 1325 K, between BaGdCuS₃ and BaS at 64.0 mol % BaS and T = 1625 K, between Cu₂S and BaGdCuS₃ at 8.0 mol % BaGdCuS₃ and T = 1125 K, between Gd₂S₃ and BaGdCuS₃ at 64.0 mol % Gd₂S₃ and 1495 K, and between BaGdCuS₃ and BaGd₂S₄ at 35 mol % BaGd₂S₄ and T = 1660 K.     

Phase equilibria in the Ce<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Ce₂O₃-K₂O-P₂O₅ ternary system has been investigated by thermoanalytical methods (DTA, DSC), powder X-ray diffraction, XPS and IR spectroscopy. The existence of three double potassium-cerium(III) phosphates has been confirmed and a new binary phosphate K₄Ce₂P₄O₁₅ has been found. Phase diagram and isothermal section at room temperature of the system Ce₂O₃-K₂O-P₂O₅ have been presented.     

Physicochemical Aspects of Development of Multicomponent Chalcogenide Phases Having the Tl<Subscript>5</Subscript>Te<Subscript>3</Subscript> Structure: A Review

The literature data on ternary structural analogues of the compound Tl₅Te₃ and multicomponent phases based on them are systematized. This class of inorganic substances is of considerable scientific and practical interest as promising functional materials having thermoelectric, optical, and magnetic properties, as well as topologically protected surface states and superconductivity. The focus of the survey is on phase equilibria in ternary and more complex systems where structural analogues of Tl₅Te₃ are formed. Crystalstructure features, thermodynamic and some physical properties of these compounds and phases of variable composition are considered.     

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 formation in the V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> system

The solid-phase interaction in the V₂O₅-Nb₂O₅-MoO₃ system has been investigated, and the formation of a solid solution bounded by the compositions MoNb₂V₄O_{18 ? δ}, Mo₂NbV₅O_{21 ? δ}, Mo₂Nb₃V₃O_{21 ? δ}, and Mo₄Nb₉V₉O_{57 ? δ} has been found (δ is nonstoichiometry). In the V₂O₅?Nb₂O₅ system, the formation of three compounds is verified, namely, VNbO₅ (tetragonal structure), VNb₉O₂₅, and V₂Nb₂₃O_62.5. The first two compounds are isostructural and form a continuous solid solution with tetragonal symmetry. A new compound of the composition Mo₃NbVO_{14 ? δ} has been synthesized. This compound is isostructural to the Mo₃Nb₂O₁₄ compound described in the literature and forms a tetragonal solid solution with it. The phase equilibria in the V₂O₅-Nb₂O₅-MoO₃ system in the subsolidus region have been determined.     

Phase formation in the V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> system

Solid-phase interactions in the V₂O₅-Ta₂O₅-MoO₃ system were studied. The formation of com- pounds TaVO₅ and VTa₉O₂₅ in the V₂O₅-Ta₂O₅ binary system was verified. Tetragonal VTa₉O₂₅-base solid solutions of the general formula Ta_{5 + 4x} V_{5 − 4x} O₂₅ (x = 0.25–1) and TaVO₅-base solid solutions of the general formula Ta _x Mo_{1 − x} V_{2 − x} O_{8 − 3x} (x = 0.625–1) were found to form. Subsolidus phase equilibria in the V₂O₅-Ta₂O₅-MoO₃ were determined.     

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 equilibria in the La<Subscript>2</Subscript>S<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-La<Subscript>2</Subscript>O<Subscript>3</Subscript> ternary system

Phase equilibria in the La₂S₃-Bi₂S₃-La₂O₃ ternary system were studied by differential thermal, X-ray powder diffraction, and microstructure analyses. Phase diagrams of five vertical sections and a liquidus surface projection were plotted for the La₂S₃-Bi₂S₃-La₂O₃ system. The regions of primary crystallization of phases and coordinates of non- and monovariant equilibria were determined for the system.     

Phase equilibria and heterogenization of supercritical fluids in the K<Subscript>2</Subscript>SO<Subscript>4</Subscript>-K<Subscript>2</Subscript>CO<Subscript>3</Subscript>-H<Subscript>2</Subscript>O system

This experimental study of phase equilibria in the K₂SO₄-K₂CO₃-H₂O system at 385–500°C and pressures up to 100 MPa is directed to determine the sequence of phase transformations that generate heterogeneous supercritical fluids from the homogeneous one; the homogeneous supercritical region spreads into the ternary system from the K₂SO₄-H₂O subsystem. We found that heterogenization of supercritical fluid upon addition of K₂CO₃ starts with l₁=l₂ critical phenomena in solid saturated solutions and is attended by amalgamation of the stable immiscibility region that spreads from the K₂CO₃-H₂O system with the metastable immiscibility region that originates from the K₂SO₄-H₂O system. Our experimental results and the topological analysis of phase equilibria at temperatures above the critical point of water gave us the full scenario of the phase behavior of the title ternary system in the regions of fluid equilibria, g=l and l₁=l₂ critical phenomena, and liquid-liquid phase separation in two-, three-, and four-phase equilibria.