NEW QUATERNARY COMPOUND FeGdSbS4 IN THE FeSb2S4–FeGd2S4 SYSTEM

For the first time, the quaternary compound FeGdSbS₄ was studied using various physicochemical methods over a wide temperature range. The study of the FeSb₂S₄–FeGd₂S₄ system revealed that at a ratio of FeSb₂S₄:FeGd₂S₄ = 1:1, the quaternary compound FeGdSbS₄ forms. FeGdSbS₄ melts congruently at 1200 K and has a berthierite-type structure (a = 11.382, b = 13.896, c = 3.614 Å; Z = 4; V = 571.606 ų, space group Pbam). The specific electrical conductivity of FeGdSbS₄ at room temperature is 2×10⁻⁴ Om⁻¹·m⁻¹. FeGdSbS₄ is an impurity semiconductor. The thermal band gap ΔEg of FeGdSbS₄ is 1.31 eV. Investigation of the magnitude and sign of the thermoelectric power (TEP) and thermal conductivity in the FeSb₂S₄–FeGd₂S₄ system shows that both dependencies reach their maxima at the composition corresponding to FeGdSbS₄. The Seebeck coefficient (α) for FeGdSbS₄ is 1000 mkV/K, and the thermal conductivity is 1.32 Vt/m·K. The FeSb₂S₄–FeGd₂S₄ system is a quasi-binary section characterized by the formation of a quaternary compound FeGdSbS₄, which melts congruently and belongs to the berthierite structural type.