Features of phase equilibria and properties of phases in the Sb-Sm-Se system

The purpose of the paper is to establish the position of the tie-lines in the Sb-Sm-Se system at 450 ​°C and 620 ​°C, to determine the optical band gap of the phases. The Sb component is in equilibrium with the γ-Sm2Se3-X-Sm3Se4 (ST Th3P4) solid solution region with α-Sm2Se3. A continuous solid solution forms between the SmSb and SmSe (ST NaCl) phases, with which the Sm3Se4 and Sm4Sb3 phases are in equilibrium. The SmSb-Sm3Se4, Sm3Se4-SmSb2, SmSe-Sm3Sb2 phases are also in equilibrium. In the Sb–Sm2Se3–Se system at 450°С, the tie-line passes between the Sb2Se3–Sm2Se3, Sb2Se3-SmSe1.9 phases. In the Sb–Se system based on Sb2Se3, a solid solution of the subtraction type Sb2-X□XSe3 (X ​= ​0–0.04) is formed. In the Sb-Sm-Se system, there is a solid solution of the substitution type along the cuts from Sb2Se3 to the Sm2Se3 (7 ​mol. % Sm2Se3), SmSe1.9 (4 ​mol. % SmSe1.9) phases. The extreme compositions of solid solutions have a peritectic point. Due to the change in the position of the tie-lines in the Sb–Sm2Se3–Se system at 620 ​°C, additional phases appear in the equilibrium samples from the Sb2Se3–Sm2Se3 section (annealing at 450 ​°C) when heated above 620 ​°C: Sb, SmSe1.9. The optical band gap of the phases is: Sb2-xSmxSe3 solid solution 1.17–1.19 ​eV, α-Sm2Se3 1.62 ​eV. Optical properties of incommensurate SmSe1.9 crystal that were investigated for the first time for this class of crystals indicate complex electronic structure that can be characterized as a multi band gap one, with at least two values of the band gap, 1.08 and 1.68 ​eV. Using optical spectroscopy, Sm ions in SmSe1.9 are proved to be predominantly in 3+ oxidation state. Previously, the formation of ternary compounds in the system was reported in the literature. Carefully conducted research allows us to assert their absence. [Display omitted] •The conditions for obtaining equilibrium samples in the Sb-Sm-Se system were established.•Sb is in equilibrium with the γ-Sm2Se3-X-Sm3Se4 solid solution.•In the Sb-Sm-Se system at 450 and 620 ​°C, 18 tie-lines and 15 subsystems were identified.•In the Sb–Se system based on Sb2Se3, a solid solution of the subtraction type Sb2-XXSe3 (x ​= ​0–0.04) is formed.•The optical band gap of the phases is: Sb2-xSmxSe3 solid solution 1.17–1.19 ​eV, α-Sm2Se3 1.62 ​eV, SmSe1.9 1.68 ​eV.