Interactions and glass formation in the TlAs2Se4-Tl3As2Se3Te3 system

The TlAs₂Se₄-Tl₃As₂Se₃Te₃ system was studied using differential thermal analysis (DTA), powder X-ray diffraction, microstructure observation, and microhardness and density measurements. A phase diagram of the title system was constructed. This system is a quasi-binary join of the TlSe-As₂Se₃-As₂Te₃ quasi-ternary system. All alloys of the system under standard conditions are prepared in the glassy form. The system has a eutectic, which contains 50 mol % Tl₃As₂Se₃Te₃ and melts at 150°C. The TlAs₂Se₄-base solid solution in the system extends to 12 mol % Tl₃As₂Se₃Te₃, and Tl₃As₂Se₃Te₃-based solid solution extends to 20 mol % TlAs₂Se₄.     

Physicochemical study of the Sb2Se3-Ho2Se3 system

The chemical interaction in the Sb₂Se₃-Ho₂Se₃ system was studied by physicochemical analysis methods (by differential thermal, X-ray powder diffraction, and microstructural analyses and also by density and microhardness measurements). The state diagram of the system was constructed. It was found that the Sb₂Se₃-Ho₂Se₃ section is a quasi-binary section of the Ho-Sb-Se ternary system. In the system, the compound HoSbSe₃ forms, which melts incongruently at 1050 K and crystallizes in the rhombic system at the unit cell parameters a = 11.855 Å, b = 11.316 Å, c = 4.139 Å, and Z = 4 in the space group Pbnm-D _2h ¹⁶ . The solubility of solid solutions based on Sb₂Se₃ at room temperature reaches 8 mol % Ho₂Se₃, whereas solid solutions based on Ho₂Se₃ were not detected.     

Phase equilibria in the InS-Sb2Te3 system

The interaction character of the InS-Sb₂Te₃ system was studied by differential thermal analysis, X-ray powder diffraction, microstructure examinations, microhardness measurements, and density determinations, and its phase diagram was constructed. The InS-Sb₂Te₃ phase diagram is a partially non-quasi-binary section of the In,Sb∥S,Te ternary reciprocal system. Two compounds are formed in the InS-Sb₂Te₃ system, namely: In₃Sb₂S₃Te₃ and InSb₂Te₃S. Sb₂Te₃-based solid solutions at room temperature have an extent of up to 6 mol % InS, while InS-based solid solutions are virtually nonexistent.     

Synthesis of GdBiTe1.5Se1.5 single crystals

GdBiTe_1.5Se_1.5has been synthesized in the Gd₂Te₃-Bi₂Se₃ system at a component ratio of 1: 1. The compound congruently melts at 800 K. GdBiTe_1.5Se_1.5 single crystals have been prepared by a gas-trans-port reaction. The compound crystallizes in a tetradymite-like rhombohedral structure. The unit cell parameters are a = 4.00 Å, c = 30.36 Å, space group $R\bar 3m$ ..     

Physicochemical study of SmTe-In2Te3 and SmTe-InTe systems

SmTe-In₂Te₃ and SmTe-InTe quasi-binary joins were studied using physicochemical methods. The SmTe-In₂Te₃ system forms two compounds, SmIn₂Te₄ and SmIn₄Te₇, which melt incongruently at 1075 and 960 K, respectively. An In₂Te₃-base solid solution at 400 K extends to 3 mol % SmTe. The SmTe-InTe system at the component ratio 3: 2 (mol/mol) forms the ternary compound Sm₃In₂Te₅, which melts with decomposition at 970 K. The InTe-based solubility range is 10 mol % SmTe.     

Synchrotron-radiation photoemission study of the V–VI layered compounds Bi2Te3, Bi2Se3, Sb2 Te3 and Sb2Te2Se

The valence band (VB) density of states and the binding energies of the weakly bound core levels have been measured by XUV photoelectron spectroscopy using synchrotron radiation for four V–VI layered compounds. Chemical shifts of the core levels are determined which support the partial ionicity of the bonds involved. The chemical shifts of the emission from two unequivalent crystal sites were shown to differ by less than 30 meV for the compounds Bi₂Te₃, Bi₂Se₃ and Sb₂Te₃.VB and core-level photoemission spectra for the V–VI compounds Bi₂Te₃, Bi₂Se₃, Sb₂Te₃ and Se₂Te₂Se have been presented. Chemical shifts of the Te 4d, Bi 5d, Sb 4d and Se 3d levels were determined, indicating partial ionicity of the mainly covalent bonds involved. Chemical-shift differences originating from atoms at two different crystal sites are <30 meV. In a simple model this implies that similar charge transfers do occur even though completely different bond orbitals were proposed for the and the AB⁽²⁾ bonds. Finally, the fact that no surface core-level shifts were observed tends to confirm the very weak influence of the van der Waals-like bonds on the B⁽²⁾ atoms.     

SnSbBiTe4-2Bi2Te3 join of the SnTe-Bi2Te3-Sb2Te3 quasi-ternary system

This is the first study of the SnSbBiTe₄-2Bi₂Te₃ join of the SnTe-Bi₂Te₃-Sb₂Te₃ quasi-ternary system by the methods of complex physicochemical analysis over a wide range of concentrations. A phase diagram was constructed for the title quasi-binary join. The system was found to be of the eutectic type; the eutectic coordinates are 65 mol % Bi₂Te₃ and 675 K. The starting components were shown to form solid solutions with extents of 20 mol %. Alloys with compositions lying within the Bi₂Te₃-based solid solution region were found to be n-type semiconductors.     

Molecular building blocks for solid‐state chalcogenides: solvothermal synthesis of [Mn(en)3]Te4 and [Fe(en)3]2(Sb2Se5)

Two new molecular metal chalcogenides, tris­(ethyl­enedi­amine‐N,N′)­manganese(II) tetratelluride, [Mn(C₂H₈N₂)₃]Te₄, (I), and bis­[tris­(ethyl­enedi­amine‐N,N′)­iron(II)] penta­seleno­diantimonate(III), [Fe(C₂H₈N₂)₃]₂(Sb₂Se₅), (II), containing the isolated molecular building blocks Te₄^2? and Sb₂Se₅^4?, have been synthesized by solvothermal reactions in an ethyl­enedi­amine solution at 433 K. The anion Te₄^2? in (I) is a zigzag oligometric chain with Te—Te bond lengths in the range 2.709–2.751 Å. There is a very short contact [3.329 (1) Å] between a pair of neighboring Te₄^2? anions. In (II), each Sb atom is surrounded by three Se atoms to give a tripodal coordination. One of the three independent Se atoms is a μ₂‐bridging ligand between two Sb atoms; the other two are terminal.     

Syntheses, structures, magnetism, and optical properties of gadolinium scandium chalcogenides

Three gadolinium scandium chalcogenides have been synthesized using Sb₂Q₃ (Q=S, Se) fluxes at 975 °C. Gd_3.04Sc_0.96S₆, GdScS₃, and Gd_1.05Sc_0.95Se₃ are crystallized in U₃ScS₆ type, GdFeO₃ type, and UFeS₃ type structures, respectively. The magnetic susceptibilities for these compounds follow the Curie-Weiss law above their transition temperatures. The effective magnetic moments are close to calculated values for free Gd³⁺ ions. The Weiss constants for Gd_3.04Sc_0.96S₆, GdScS₃, and Gd_1.05Sc_0.95Se₃ are determined to be −3.3(1), −4.5(4), and 1.5(1) K, respectively. Gd_3.04Sc_0.96S₆ orders antiferromagnetically below 9 K. GdScS₃ exhibits an antiferromagnetic ordering below 3 K with a weak ferromagnetism. Gd_1.05Sc_0.95Se₃ undergoes a ferromagnetic transition around 5 K. The optical band gaps for Gd_3.04Sc_0.96S₆, GdScS₃, and Gd_1.05Sc_0.95Se₃ are 1.5, 2.1, and 1.2 eV, respectively.     

The heat capacity of solid antimony telluride Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>

The literature data on the heat capacity of solid antimony telluride over the range 53–895 K were analyzed. The heat capacity of Sb₂Te₃ was measured over the range 350–700 K on a DSM-2M calorimeter. The equation for the temperature dependence was suggested. The thermodynamic functions of Sb₂Te₃ were calculated over the range 298.15–700 K.     

Propriétés thermiques et optiques des verres du système Sb2S3–As2S3–Sb2Te3

Thermal and optical properties of glasses of the Sb₂S₃–As₂S₃–Sb₂Te₃ system. The glass-forming region of Sb₂S₃–As₂S₃–Sb₂Te₃ is very wide. The As₂S₃ compound supports the formation of prepared glasses and their stability. They have only one glass-transition temperature (T_g), which varies from 167 to 214 °C. It drops when the content of Sb₂Te₃ increases. This semi-metal compound supports the crystallization of glasses in several stages. Whereas the optical gap (E_g) increases with the content of As₂S₃ in the Sb₂S₃–As₂S₃ and Sb₂Te₃–As₂S₃ binary systems, it is practically constant in the ternary one on the cut with 20% of Sb₂Te₃, and is worth on average 1.04 eV.     

Interaction in the TlSe-Pr2Se3 system

The interaction of components in the TlSe-Pr₂Se₃ system was studied by differential thermal, X-ray powder diffraction, and microstructural analyses and also by microhardness and density measurements. The state diagram of this system was constructed. It was found that the section TlSe-Pr₂Se₃ is a quasi-binary section of the Tl-Pr-Se ternary system. In the TlSe-Pr₂Se₃ system at the component ratio 1: 1, a new chemical compound, TlPr₂Se₄, forms, which melts congruently at 1295°C. In the system based on TlSe, solid solutions form until 3.5 mol % Pr₂Se₃, and in the system based on Pr₂Se₃, solid solutions occur until 2.5 mol % TlSe.     

Thermoelectric properties of p-type pseudo-binary (Ag0.365Sb0.558Te)x-(Bi0.5Sb1.5Te3)1−x (x=0-1.0) alloys prepared by spark plasma sintering

In this paper, pseudo-binary (Ag_0.365Sb_0.558Te)_x-(Bi_0.5Sb_1.5Te₃)_1−x (x=0-1.0) alloys were prepared using spark plasma sintering technique, and the composition-dependent thermoelectric properties were evaluated. Electrical conductivities range from 7.9×10⁴ to 15.6×10⁴ Ω⁻¹ m⁻¹ at temperatures of 507 and 318 K, respectively, being about 3.0 and 8.5 times those of Bi_0.5Sb_1.5Te₃ alloy at the corresponding temperatures. The optimal dimensionless figure of merit (ZT) of the sample with molar fraction x=0.025 reaches 1.1 at 478 K, whereas that of the ternary Bi_0.5Sb_1.5Te₃ alloy is 0.58 near room temperature. The results also reveal that a direct introduction of Ag_0.365Sb_0.558Te in the Bi-Sb-Te system is much more effective to the property improvement than naturally precipitated Ag_0.365Sb_0.558Te in the Ag-doped Ag-Bi-Sb-Te system.     

MnS-Ln2S3 (Ln = La, Nd, or Gd) phase diagrams; thermodynamics of phase transitions

The MnS-La₂S₃ phase diagram has been constructed where the incongruently melting compound Mn₂La₆S₁₁ is formed. Complex sulfide Mn₂La₆S₁₁ is characterized by monoclinic structure; its incongruent melting temperature is 1535 K. Eutectic coordinates are 31 mol % La₂S₃, 1490 K. The extent of the ??-La₂S₃ based solid solutions at 1570 K is 8 mol % MnS; at 770 K, ??-La₂S₃ dissolves 3 mol % MnS. The MnS-Gd₂S₃ system is a eutectic with limited solid solutions. Eutectic coordinates are 35.5 mol % Gd₂S₃, 1640 K. Solubility in ??-Gd₂S₃ is 28 mol % MnS at 1570 K, in ??-Gd₂S₃ is 13 mol % MnS at 1170 K, and in MnS is 1 mol % Gd₂S₃. Thermochemical equations have been composed for eutectic and eutectoid phase transformations. A MnS-Nd₂S₃ phase diagram has been predicted.     

Phase diagrams of the systems Ln2S3-Ln2O3 (Ln = Gd, Dy)

For the first time, the phase diagrams of the systems Gd₂S₃-Gd₂O₃ and Dy₂S₃-Dy₂O₃ were constructed within the temperature range from 870 K to the melting point. In the systems, compounds Gd₂O₂S and Dy₂O₂S form in hexagonal symmetry with the unit cell parameters a = 0.3858 nm, c = 0.6667 nm and a = 0.3802 nm, c = 0.6591 nm, respectively. The compounds melt congruently at 2430 and 2370 K, respectively. Their microhardnesses are 4900 and 5150 MPa, respectively. The coordinates of eutectics are the following: 21 mol % Gd₂O₃, T _eu = 1875 K; 83 mol % Gd₂O₃, T _eu = 2270 K; 20 mol % Dy₂O₃, T _eu = 1780 K; and 81 mol % Dy₂O₃, T _eu = 2220 K.     

The Sections GeSnSb<Subscript>4</Subscript>Te<Subscript>8</Subscript>–GeTe and GeSnSb<Subscript>4</Subscript>Te<Subscript>8</Subscript>–SnTe of the Quasi-Ternary System GeTe–Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–SnTe

By differential thermal, X-ray powder diffraction, and microstructural analyses and microhardness and density measurements, phase equilibria in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe were studied and their state diagrams were constructed. It was determined that these sections are quasi-binary sections of the eutectic type of the GeTe–Sb₂Te₃–SnTe system. The coordinates of the eutectic points in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe are (40 mol % GeTe, 700 K) and (30 mol % SnTe, 750 K), respectively. Regions of solid solutions based on the initial components in the sections were identified. Alloys in the regions of solid solutions are p-type semiconductors.     

Phase equilibria in the GeTe-Sb2Te3-Bi2Te3 quasi-ternary system

Phase equilibria in the GeTe-Sb₂Te₃-Bi₂Te₃ system were studied by differential thermal analysis, X-ray powder diffraction, and metallography and also by microhardness and density measurements in the polythermal sections GeSb₂Te₄-GeBi₂Te₄, GeTe-GeSbBiTe₄, GeSb₄Te₇-GeSbBiTe₄, GeSbBiTe₄-Sb₂Te₃, GeSbBiTe₄-Bi₂Te₃, and Ge₂Sb₂Te₅-GeSbBiTe₄, which are quasi-binary and partially quasi-binary sections. A quaternary compound of the composition GeSbBiTe₄ was synthesized for the first time, which crystallizes in the trigonal system (space group $R\bar 3m - D_{3d}^5$ ) with the unit cell parameters a = 6.27 Å and c = 38.40 Å (melting point 850 K).     

Rapid solid-state synthesis of binary group 15 chalcogenides using microwave irradiation

Solid-state microwave synthesis was found to provide a simple, rapid and economical route to prepare Sb₂Se₃, Sb₂Te₃, Bi₂Se₃ and Bi₂Te₃. These technologically important materials were prepared via solid-state microwave synthesis in as little as 4 min. Through the process of finding the ideal synthetic conditions with which to produce each of these compounds, the effects that several synthetic variables have on the reaction outcomes were explored. Scanning electron microscopy, energy dispersive spectroscopy, powder X-ray diffraction, differential thermal analysis and diffuse reflectance measurements, when appropriate, were used to characterize the materials.     

Interaction between Cr2Se3 and Cu2GeSe3

The interaction along the Cu₂GeSe₃-Cr₂Se₃ join has been investigated using differential thermal and X-ray powder diffraction analyses. It has been found that the join is quasi-binary with a degenerate eutectic based on the Cu₂GeSe₃ compound. Two new quaternary compounds have been found along the join, namely, Cu₂GeCr₆Se₁₂ and the γ phase. The phase is formed at 915°C by the peritectic reaction L + β-Cr₂Se₃ = γ and has the primary crystallization region up to 9 mol % Cr₂Se₃ in the temperature range 758–915°C. The room-temperature homogeneity range of the γ phase is 65–70 mol % Cr₂Se₃. The Cu₂GeCr₆Se₁₂ compound is formed by the peritectoid reaction γ + β-Cr₂Se₃=Cu₂GeCr₆Se₁₂ at 880°C, and its homogeneity range is 73–79 mol %. The X-ray reflections of the γ phase are indexed for the tetragonal crystal system with the unit cell parameters a = 12.043 Å and c = 9.180 Å. Samples with ferromagnetic properties are found in the homogeneity regions of both compounds.     

Thermal properties of some compositions in the chalcogenide system Sb40Te60-xSex

The thermal diffusivities, specific heats and thermal conductivities of the binary compositions Sb₄₀Te₆₀ and Sb₄₀Se₆₀ and the ternary composition Sb₄₀Te₃₀Se₃₀ were measured in the range 320 to 500 K. It was found that the environmental temperature, the content of Se in the composition and the conditions of measurements are decisive factors greatly influencing both the values and the behaviour ot the thermal parameters, and the mechanisms of thermal transport. Although the tested compositions exhibit semiconducting behaviour, the free charge carrier component of the thermal conductivity was so small as to be negligible. Thus, it could be concluded that the observed thermal conductivity is attributable to both photon and phonon mechanisms.

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Zusammenfassung Im Temperaturbereich 320–500 K wurde das Temperaturleitvermögen, die spezifische Wärme und die Wärmeleitfähigkeit der binären Kompositionen Sb₄₀Te₆₀ bzw. Sb₄₀Se₆₀ und der ternären Komposition Sb₄₀Te₃₀Se₃₀ untersucht. Man fand, daß die Umgebungstemperatur, der Se-Gehalt der Kompositionen und die Meßbedingungen entscheidende Faktoren sind, welche sowohl Wert als auch Verhalten der thermischen Parameter, weiterhin den Mechanismus des Wärmetransportes beeinflussen. Obwohl die untersuchten Kompositionen Halbleiterverhalten zeigten, war die freie Ladungsträgerkomponente der Wärmeleitfähigkeit so gering, daß sie vernachlässigt werden konnte. Somit konnte darauf geschlossen werden, daß die beobachtete Wärmeleitfähigkeit sowohl Photonen- als auch Phononenmechanismen zugeschrieben werden kann.