Crystal structure, thermal expansion, dielectric permittivity and phase transitions of Bi2S3

The crystal structure of Bi2S3 both natural (bismuthinite) and synthetic, r eported in the literature, was determined at ambient temperature in the non -polar space group Pbnm. Physical properties of Bi2S3 indicate, however, on the possible phase transitions both in the high and low temperature region s. Precise lattice parameters measured as a function of temperature have sh own weak anomalies at 160 and 410 K. The phase transition above 400 K has b een also confirmed by measurements of microwave dielectric permittivity alo ng the c-axis. The crystal structure of Bi2S3 has been determined at 130, 2 95 and 460 K. At all three temperatures the crystal structure was successfu lly refined in the space group Pbnm. The weak phase transitions observed in Bi2S3 apparently do not change the symmetry, or these changes are too smal l to be detected at the present level of accuracy of the X-ray crystal stru cture determination.