Preparation of terbium sesquisulfide and holmium sesquisulfide by sulfurization of their oxide powders using CS2 gas

The formation behaviors of terbium sesquisulfide (Tb2S3) and holmium sesquisulfide (Ho2S3) synthesized via the sulfurization of their oxide powders using CS2 gas in the range of temperature 673 to 1323 K were investigated. In the sulfurization of Tb4O7 powder, Tb2O3, and Tb2O2S were formed in the initial stage of reaction, and alpha-Tb2S3 was finally formed at higher temperature. For long sulfurization time of 8 h, single-phase alpha-Tb2S3 could be synthesized at 1323 K. In the sulfurization of Ho2O3 powder using CS2 gas, only Ho2O2S was formed as an intermediate product. At a sulfurization temperature above 873 K, Ho2O2S was formed in the initial stage of reaction, and single-phase delta-Ho2S3 was formed at 1323 K for 8 h instead of Ho2O2S. Furthermore, the influence of the addition of carbon black to the sulfurization of Ho2O3 powder using CS2 gas was investigated, and the result implied that the reactions were accelerated slightly by the addition of carbon black.