Phase equilibria and some properties of solid solutions in the Tl5Te3-Tl9BiTe6-Tl5Te2Br system

Phase equilibria in the Tl₅Te₃-Tl₉BiTe₆-Tl₅Te₂Br system were studied by differential thermal analysis, X-ray powder diffraction, and measurements of microhardness and also emf relative to a thallium electrode. Polythermal and isothermal sections of the phase diagram at 760 and 800 K, and projections of the liquidus and solidus surfaces were constructed. The unit cell parameters, microhardness, and emf in the alloys were described as functions of concentration. The system is characterized by the formation of complete solid solutions with the Tl₅Te₃ structure.     

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 Tl-TlBr-Te system and thermodynamic properties of the compound Tl5Te2Br

The Tl-TlBr-Te composition region of the Tl-Te-Br phase diagram has been explored by DTA, X-ray diffraction, microhardness measurements, and electromotive force (emf) measurements relative to a thallium electrode in concentrations cells. The phase diagrams along a number of joins, the isothermal section at 400 K of the phase diagram, and a projection of the liquidus surface have been constructed. Extensive phase-separation areas, including a three-liquid-phase field in the Tl-TlBr-Tl₂Te subsystem, have been revealed. The homogeneity ranges and primary crystallization fields of phases have been mapped, and the coordinates of nonvariant and univariant equilibria in the T-x-y diagram have been determined. The standard thermodynamic functions of formation of the Tl₅Te₂Br compound and its standard entropy have been derived from emf data.     

Phase equilibria and some properties of solid solutions in the Tl5Te3-Tl9BiTe6-Tl5Te2Cl system

Phase equilibria in the Tl₅Te₃-Tl₉BiTe6-Tl₅Te₂Cl system were studied by differential thermal analysis (DTA), X-ray powder diffraction, and measurements of microhardness and also emf of concentration circuits with reference to a thallium electrode. A number of polythermal sections, the isothermal sections of the phase diagram at 760 and 800 K, and projections of the liquidus and solidus surfaces were constructed. It was shown that the system is characterized by the formation of unlimited solid solutions with the Tl₅Te₃ structure. The concentration dependences of the crystal lattice parameters, microhardness, and emf in the solid solutions were described.     

NQR study of ternary chalcogenides A3BX3, ABX2, and ABX where A = Cu,Ag, or TI, B = As or Sb,and X = S or Se

¹²¹Sb, ¹²³Sb, ⁷⁵As, ⁶³Cu, and ⁶⁵Cu NQR resonances are reported for CuSbSe₂, Tl₃SbSe₃, Tl₃SbS₃, Tl₃AsS₃, Tl₃AsSe₃, Ag₃AsSe₃, TlSbS₂, CuAsS, AgAsS, and Cu₅SbS₃I₂. Tl₃SbSe₃ is an incongruently melting compound not observed in an earlier phase-diagram study of the pseudobinary system Tl₂SeSb₂Se₃. For isostructural arsenic and antimony chalcogenides the ratio of ⁷⁵As to ¹²¹Sb quadrupole coupling constants is 0.42, and for the BX₃ group in binary or ternary corresponding pairs of sulfide and selenides the ratio of quadrupole coupling constants for ⁷⁵As or ¹²¹Sb is 0.83. A reversible phase transition was observed at 130 K for Ag₃AsSe₃. Unit cell parameters are reported for crystals of TlSbS₂ and Cu₅SbS₃I₂.     

Thermodynamic study of the Ag-As-Se and Ag-S-I systems using the EMF method with a solid Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript> electrolyte

The EMF method with a solid Ag₄RbI₅ superionic conductor was used to study the Ag-As-Se and Ag-S-I systems in the composition ranges of Ag₂Se-As₂Se₃-Se and Ag₂S-AgI-S, accordingly. Their solid-phase equilibrium diagrams are constructed or specified. The existence of ternary AgAs₃Se₅, AgAsSe₂, Ag₃AsSe₃, Ag₇AsSe₆, Ag₃SI compounds is confirmed. The standard partial and integral thermodynamic formation functions and also standard entropies were calculated for these compounds for the first time.     

Reciprocal system 3Tl2S + Bi2Se3 ↔ 3Tl2Se + Bi2S3

The reciprocal system 3Tl₂S + Bi₂Se₃ ? 3Tl₂Se + Bi₂S₃ has been investigated by DTA, X-ray powder diffraction analysis, and emf measurements. Some polythermal sections and the isothermal section at 500 K of the phase diagram and the projection of the liquidus surface of this system have been constructed, and the types and coordinates of the invariant and univariant equilibria have been determined. The existence of wide regions of quaternary solid solutions based on the binary compounds Tl₂S, Tl₂Se, Bi₂S₃, and Bi₂Se₃, and solid solutions between the temary compounds TlBiS₂ and TlBiSe₂ have been established.     

Phase equilibria in the Ag2Te-PbTe-Bi2Te3 system

Phase equilibria in the Ag₂Te-PbTe-Bi₂Te₃ quasi-ternary system were studied by differential thermal analysis, X-ray powder diffraction, and measurements of microhardness and emf of concentration circuits with an Ag₄RbI₅ solid electrolyte. Some polythermal sections and isothermal (600 and 800 K) sections of the phase diagram, and also a projection of the liquidus surface were constructed. The primary crystallization fields of phases were determined, and the types and coordinates of invariant and monovariant equilibria were found. The system is characterized by the formation of a wide continuous band of high-temperature solid solutions (γ phase) with a cubic structure along the PbTe-AgBiTe₂ section. With decreasing temperature (T ≤ 715 K), AgBiTe₂ and γ solid solutions, close in composition to this compound, experience solid-phase decomposition to form Bi₂Te₃, ternary tetradymite-like phases of the PbTe-Bi₂Te₃ boundary system, and the low-temperature phase of Ag₂Te.     

Phase equilibria and thermodynamic properties of the system Tl-TlCl-Se

Phase equilibria in the system Tl-Se-Cl were studied in the region Tl-TlCl-Se by DTA, X-ray powder diffraction, emf measurements concentration circuits (−) Tl/glycerol + KCl + TlCl/(Tl-Se-Ce) (+), and microhardness measurements. Several vertical sections, an isothermal section at 400 K, and the liquidus-surface projection were constructed. The primary crystallization regions and homogeneity regions of phases were determined, including the α phase of variable composition based on Tl₅Se₂Cl, the only ternary compound of the system. The types and coordinates of invariant and monovariant equilibria on the T-x-y diagram were determined. From the results of emf measurements, the standard thermodynamic functions of formation and the standard entropy were calculated for the compound Tl₅Se₂Cl. Original Russian Text ￠ D.M. Babanly, Yu.A. Yusibov, M.B. Babanly, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 5, pp. 819–826.     

Compounds in the system Cu2SeAs2Se3

The phase diagram Cu₂SeAs₂Se₃ was investigated by thermal and X-ray methods. Cu₂Se has a limited solubility for As₂Se₃ (5 mole% at 769 K). The stoichiometric compound Cu₃AsSe₃ exists between 696 and 769 K. Cu₄As₂Se₅, a phase at 66.6 mole% Cu₂Se, decomposes peritectically at 746 K. The narrow homogeneity range (4 mole% at 683 K) extends far into the ternary space. CuAsSe₂ also decomposes peritectically at 683 K. A degenerated eutectic between CuAsSe₂ and As₂Se₃ was found at 641 K. Single crystals of Cu₄As₂Se₅ were grown in a salt melt. A metastable modification of the high-temperature phase Cu₃AsSe₃ can be obtained by quenching. Cu₄As₂Se₅ (space group R3, lattice constants a = 1404.0(1) pm, c = 960.2(1) pm), Cu₆As₄Se₉, obtained by Cambi and Elli, and Cu₇As₆Se₁₃ of Takeuchi and Horiuchi are different versions of a sphalerite-type compound with a broad homogeneity range in the system CuAsSe. CuAsSe₂ is possibly monoclinic with lattice parameters of a = 946.5(1) pm, b = 1229.3(1) pm, c = 511.7(1) pm, and β = 98.546(4)°. The enthalpy of mixing of Cu₂Se and As₂Se₃ in the liquid state is endothermic.     

Conductivity and Raman spectroscopy of new indium(I) and thallium(I) ionic conductors. In4CdI6, In2ZnI4, and Tl2ZnI4, and the related compound Tl4CdI6

The new compound Tl₂ZnI₄ has been prepared and characterized by Raman spectroscopy, powder X-ray diffraction, elemental analyses, and a partial binary phase diagram. The compounds In₄CdI₆, Tl₄CdI₆, and In₂ZnI₄, for which phase diagrams are available in the literature, were characterized by Raman spectroscopy and their identities were confirmed by elemental analyses and X-ray powder diffraction. Each of these materials, except Tl₄CdI₆, undergoes a sharp order-disorder phase transition at elevated temperatures that can be detected by the measurement of Raman spectra as a function of temperature. Conductivity measurements as a function of temperature, using both reversible and blocking electrodes, reveal a high ionic conductivity in the disordered, high-temperature phase. This work suggests that indium(I) and thallium(I) ionic conductors may exist, analogous to some well-known double salt conductors based on simple silver(I) and copper(I) halides. In addition, the present study demonstrates the usefulness of Raman spectroscopy in the characterization of heavy-metal ionic conductors.     

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).     

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.     

Dimensional reductions from 2-D Nb4P2S21 to 1-D ANb2PS10 (A=Na, K, Rb, Cs, Tl) and to 0-D Tl5[Nb2S4Cl8]Cl using halide molten salts

We found new synthetic routes to obtain 1-D quaternary thiophosphate compounds and a 0-D molecular complex containing a Nb₂S₄ core from a 2-D ternary thiophosphate, Nb₄P₂S₂₁. When Nb₄P₂S₂₁ was reacted with alkali metal halides (ACl; A=Na, K, Rb, Cs) or TlCl at 500-700 °C, the -S-S-S- bridges in 2-D Nb₂PS₁₀-S-S₁₀PNb₂ were excised to form a 1-D chain, and cations were inserted between the chains to form ANb₂PS₁₀ (A=Na, K, Rb, Cs, Tl). We also found that thallium chloride (TlCl) is an excellent reagent for further excision, and it substitutes chloride ligands for the sulfur ligands of 2-D Nb₄P₂S₂₁ to form the molecular complex Tl₅[Nb₂S₄Cl₈]Cl. Crystal data for TlNb₂PS₁₀: monoclinic, Pn, a=6.9452(11) Å, b=7.3761(12) Å, 12.873(2) Å, β=104.472(3)°, and Z=2. Crystal data for Tl₅[Nb₂S₄Cl₈]Cl: orthorhombic, Immm, a=7.001(5) Å, b=9.509(7) Å, c=15.546(11) Å, and Z=2.     

Effet Mössbauer de 119Sn dans les systèmes SnSBaS et SnSTl2S

Tin-119 Mössbauer spectra have been recorded at liquid nitrogen and room temperatures for ternary sulfides isolated from the systems SnSBaS and SnSTl₂S. The chemical isomer shifts observed (2.8 – 3.4 mm/sec relative to BaSnO₃ at 293 K) are characteristic of divalent tin compounds. The data are consistent with the known structures of these compounds and are discussed with regard to the stereochemical activity of the tin(II) lone pair of electrons. For Tl₂Sn₂S₃ and Tl₄SnS₃ the Mössbauer parameters are interpreted in terms of direct population of conductance bands by nonbonding electron pairs.     

On basic thallium sulfates: Structure of Tl2Tl OH(SO4)2

The Tl₂TlOH(SO₄)₂ compound is monoclinic, a = 7.758 (3), b = 17.587 (9), c = 7.356 (3) Å, β = 119.91 (3)°, S. G. Cc, Z = 4. The structure was solved by full-matrix least square refinement to R = 0.033 from 1242 single-crystal reflections collected on an automated diffractometer. Tl⁺ ions ensure bonding between [Tl^IIIOH(SO₄)₂]_∞ sheets. These sheets may be viewed as criss-crossing TlSO₄ chains. In the [101] direction, the linking of Tl^III is reinforced by bidentate OH groups, so the usual hexacoordination of trivalent thallium is preserved. A transition occurring at 104°C is under investigation.     

Phase equilibria in the Tl2Te-SnTe-Bi2Te3 system

phase equilibria in the Tl₂Te-SnTe-Bi₂Te₃ system were studied by differential thermal analysis (DTA), X-ray powder diffraction, and microhardness measurements. Some polythermal sections and isothermal (at 600 and 800 K) sections of the phase diagram and a projection of the liquidus surface were constructed. It was shown that the system is characterized by the formation of solid solutions with the Tl₅Te₃ structure (δ) and solid solutions based on SnTe (γ₁), Tl₂Te (α), Bi₂Te₃ (β), and two TlBiTe₂ (γ₂ and γ′₂) phases. Their homogeneity regions were determined. The liquidus surface consists of the primary crystallization fields of the β-, γ₁-, γ′₂-, and δ phases and the compounds SnBi₂Te₄ and SnBi₄Te₇. The liquidus of the α phase is degenerate. The primary crystallization fields of phases were determined, and the types and coordinates of in- and monovariant equilibria were found.     

The standard free energy of formation of YbFe2O4, Yb2Fe3O7, YbFeO3, and Yb3Fe5O12 at 1200°C

The standard free energy of formation of YbFe₂O₄, Yb₂Fe₃O₇, YbFeO₃, and Yb₃Fe₅O₁₂ from metallic iron, Yb₂O₃, and oxygen was determined to be ?100.38, ?158.38, ?58.17, and ?283.40 kcal/mole, respectively, at 1200°C on the basis of the phase equilibria in the FeFe₂O₃Yb₂O₃ system. The FeFe₂O₃-Lanthanoid sesquioxide systems were classified into four types with respect to the assemblage of the ternary compounds in stable existence at 1200°C, and the standard free energy of formation of YbFeO₃ was compared with those of the other lanthanoid-iron perovskites.     

New thallium iodates—Synthesis, characterization, and calculations of Tl(IO3)3 and Tl4(IO3)6, [Tl3Tl(IO3)6]

Two new thallium iodates have been synthesized, Tl(IO₃)₃ and Tl₄(IO₃)₆ [Tl⁺₃Tl³⁺(IO₃)₆], and characterized by single-crystal X-ray diffraction. Both materials were synthesized as phase-pure compounds through hydrothermal techniques using Tl₂CO₃ and HIO₃ as reagents. The materials crystallize in space groups R-3 (Tl(IO₃)₃) and P-1 (Tl₄(IO₃)₆). Although lone-pairs are observed for both I⁵⁺ and Tl⁺, electronic structure calculations indicate the lone-pair on I⁵⁺ is stereo-active, whereas the lone-pair on Tl⁺ is inert.     

Thermodynamic studies on SrFe12O19(s), SrFe2O4(s), Sr2Fe2O5(s) and Sr3Fe2O6(s)

The citrate-nitrate gel combustion route was used to prepare SrFe₂O₄(s), Sr₂Fe₂O₅(s) and Sr₃Fe₂O₆(s) powders and the compounds were characterized by X-ray diffraction analysis. Different solid-state electrochemical cells were used for the measurement of emf as a function of temperature from 970 to 1151 K. The standard molar Gibbs energies of formation of these ternary oxides were calculated as a function of temperature from the emf data and are represented as (SrFe₂O₄, s, T)/kJ mol⁻¹ (±1.7)=−1494.8+0.3754 (T/K) (970?T/K?1151). (Sr₂Fe₂O₅, s, T)/kJ mol⁻¹ (±3.0)=−2119.3+0.4461 (T/K) (970?T/K?1149). (Sr₃Fe₂O₆, s, T)/kJ mol⁻¹ (±7.3)=−2719.8+0.4974 (T/K) (969?T/K?1150).Standard molar heat capacities of these ternary oxides were determined from 310 to 820 K using a heat flux type differential scanning calorimeter (DSC). Based on second law analysis and using the thermodynamic database FactSage software, thermodynamic functions such as Δ_fH°(298.15 K), S°(298.15 K) S°(T), C_p°(T), H°(T), {H°(T)-H°(298.15 K)}, G°(T), free energy function (fef), Δ_fH°(T) and Δ_fG°(T) for these ternary oxides were also calculated from 298 to 1000 K.