Preparation, crystal structure, and electrical properties of thallium monosulfide in the vicinity of high-temperature phase transitions

Single crystals of thallium monosulfide TIS with excess sulfur (4 at. %) are grown. The existence of monoclinic (of the TIGaSe2 type), tetragonal ordered (of the TIS type), and subtetragonal phases of thallium monosulfide is revealed using x-ray powder diffraction. The temperature dependences of the electrical conductivity and permittivity of thallium monosulfide single crystals indicate that, in the temperature range 401-411 K, these crystals undergo a phase transition to a state with superionic conduction.