Study of electrical and thermoelecrical properties of sulfides Tm$_{x}$Mn$_{1-x}$S

Variable-valence Tm$_{x}$Mn$_{1-x}$S compounds have been synthesized and their structural, electrical, and thermoelectrical properties have been studied in the temperature range of 80–1100 K. The regions of existence of solid solutions of sulfides Tm$_{x}$Mn$_{1-x}$S with the NaCl-type fcc lattice have been determined. It has been found that, as thulium ions are substituted for manganese cations, the electrical resistivity increases, and the lattice parameter increases more sharply than that corresponding to the Vegard’s law. The study of the temperature dependences of the thermopower coefficient has revealed that the current carrier sign is retained to 500 K for all the substitution concentrations, and the charge carrier type changes from the hole type to the electron type with variations in the temperature. The experimental data have been explained in terms of the exciton model.