Temperature effects in (TlInS2)1–x(TlGdS2)x solid solutions

Abstract

 Alloys of the (TlInS₂)₁₋ₓ(TlGdS₂)ₓ system were synthesized, and single crystals were grown by the Bridgman method. X-ray diffraction studies established the solubility range of TlGdS₂ in TlInS₂. The linear thermal expansion coefficient (αL) and isothermal compressibility (χT) of TlInS₂ and the solid solutions (TlInS₂)₁₋ₓ(TlGdS₂)ₓ (0 ≤ x ≤ 0.10) were investigated over the temperature range of 80–400 K. Based on the experimental αL and χT values, the Debye temperature, mean-square atomic displacement, Young’s modulus, shear modulus, Poisson’s ratio, and the difference between Cp and CV were determined. The band gap was calculated from the temperature dependence of electrical conductivity and compared with values obtained using thermal and optical methods. The anomalous behavior of electrical conductivity was attributed to hopping conduction associated with stoichiometric vacancies and localized states within the band gap. Unlike TlInS₂, no phase transitions were observed in the investigated solid solutions over the temperature range of 80–400 K. Increasing the TlGdS₂ concentration resulted in higher thermal expansion and compressibility coefficients, indicating weaker interatomic interactions and enhanced anharmonicity of lattice vibrations. The obtained results reveal correlations among crystal structure, chemical bonding, and physical properties in layered chalcogenide semiconductors.