LOW-TEMPERATURE CHEMICAL ROUTES TO FORMATION AND IR PROPERTIES OF LANTHANUM SESQUISULFIDE (LA2S3) CERAMICS

Lanthanum sulfide (La2S3) exists in three different allotropic forms. in the crystalline state. The low-temperature orthorhombic phase (alpha) transforms to the intermediate tetragonal phase (beta) which further undergoes transformation to the high-temperature cubic phase (gamma). The intermediate tetragonal phase (beta) is an oxysulfide with possible use as a phosphor, and the cubic phase (gamma) of La2S3 Shows potential for application as a far IR (8-14 mum) window material. We report metal-organic synthesis routes for the preparation of the beta- and gamma-phases of La2S3 by processing modifications and choice of precursor chemistry. The alkoxide-derived precursors and the transformed sulfide powders were characterized for morphology, microstructure, and thermal stability. Phase evolution studies were also conducted, and the results are discussed in the context of formation of the beta- and gamma-phases. Results of densification, microstructure, and infrared transmission characteristics are also presented.