Formation and densification of CaLa2S4 powders by sulfidization of modified metal alkoxides in different atmospheres

Highly sinterable submicron CaLa2S4 (CLS) powders with high La/Ca ratios were prepared by sulfidizing calcium and lanthanum alkoxides under CS2 gas for 8 h and then in a pure H2S atmosphere for 8 h at 550–950°C. It is for application in infrared transmitting window of 8–14 μm wavelength. In the range of La/Ca ratios from 10 to 15, the phases obtained are LaS2 intermediate phase at low temperature (550°C), a β-La2S3 minor phase at 650°C, and a pure Th3P4 phase after 850°C treatment. After HIP’ing and annealing in an H2S atmosphere at 1350°C, the Pb0.1Ca0.9La2S4 pellet without extrinsic absorption in the 2.5–7 μm range due to carbon contamination was obtained by sulfidizing at 850°C for 8 h in CS2 gas and then at 850°C for 8 h in H2S atmosphere. The characteristic absorption bands of sulfate and sulfite at 9.2 and 11 μm were reduced by eliminating the oxygen residue in the sulfide by using the powder sulfidized at 750°C in CS2 gas and then at 850°C for 8 h in H2S atmosphere.