Effects of Sulfidization and Sintering Temperatures of CaLa₂S₄ Powder on Its Optical Property

Highly sinterable submicron CaLa₂S₄ powders were prepared by sulfidizing calcium and lanthanum alkoxides at 400°C to 1050°C for 48 h in pure H₂S atmosphere for application in infrared transmitting window material for 8-14 µm wavelength. The CaLa₂S₄ powders had some residues of carbon and hydrogen after sulfidizing at or below 850°C. The CaLa₂S₄ powder without extrinsic absorption in the 2.5-7 µm range due to the contaimination was obtained by sulfidizing at 950°C for 48 h. The characteristic absorption bands of sulfite and sulfate at 9.2 and 11 µm were reduced in the pellet by eliminating the oxygen content in the sulfide by sulfidizing the powder at 1050°C for 48 h. It was shown that 1050°C was the optimum sulfidization temperature, while 1400°C was the optimum sintering and hot isostatic pressing (HIP) temperature to obtain a higher transmittance ceramic.