Powder preparation and high infrared performance of NaLaS2 transparent ceramics

NaLaS2 powders with various Na/La molar ratios were prepared via a gas-solid reaction method where NaF nanocrystal was used as the sodium source, and CS2 served as the sulfurizing agent. The effective sulfurization parameters were designed based on the thermodynamic properties of the precursor obtained via the reverse coprecipitation way. The phase compositions and morphologies of sulfide powders depended strongly on NaF amount. The powder with a molar ratio of Na/La = 1.3 was selected for sintering NaLaS2 ceramic via hot-pressing process under vacuum due to its highest phase purity and lowest oxidesulfide, fluorosulfide impurities level. As-sintered NaLaS2 ceramic exhibited a consolidated microstructure, a minor amount of oxysulfide impurities and high 8-14 μm mean transmissivity with the maximum transmittance up to 67.5% at 9 μm. Contrasting study proves that NaLaS2 ceramic has the tendency to possess the better IR performance and antioxidation capacity than γ-La2S3 and CaLa2S4 ceramics.