Formation of Calcium Lanthanum Sulfide by Carbonate Coprecipitation and CS 2 Sulfurization

Pure calcium lanthanum sulfide (CLS) powders with various La/Ca ratios were prepared by a carbonate coprecipitation method and CS 2 sulfurization. Four coprecipitation processes were investigated by conventional titration, and a suitable means for coprecipitating CLS was found. By that process, a cation solution containing La 3+ and Ca 2+ ions was added to the precipitation medium (an anion solution of ammonium carbonate) with stirring. Precursors with various La/Ca ratios were synthesized and then sulfurized for 3 h using CS 2 as a sulfurizing agent. In the range of La/Ca ratios from 2 to 5, the intermediate phase of sulfide powder was LaS 2 , and the CLS formation temperature could be increased by increasing the La/Ca ratio. For powder with high La/Ca ratios (La/Ca = 10, 15), and LaS 2 intermediate phase formed at low temperature (700°C), a (β‐La 2 S 3 minor phase at 800°C, and a pure CLS phase after 950°C treatment. The resulting pure CLS powder was spherical, with slight necking in the submicrometer range.