Stabilization of γ-La2S3 by Ba2+ ions at low temperature

Abstract

The lanthanum sulfide γ-La2S3 with cubic Th3P4 structure has emerged as a promising long-wave infrared transparent material. However, the γ-La2S3 is only stable at high temperatures (>1300 °C). In this work, a novel method to lower the stabilization temperature is reported. Bivalent Ba ions are incorporated into the La2S3 crystal structure and the stabilization temperature of the γ-La2S3 decreased to less than 850 °C. The Ba2+-doped γ-La2S3 (γ-La2S3: Ba2+) was successfully developed using the coprecipitation reaction method and sulfidation with CS2. The high phase purity, good thermal stability, and lowest oxide sulfide impurities were obtained by Ba/La = 0.1 (in mole, abbreviated as nBa/La = 0.1). The first-principles calculation shows that the theoretical Eg of the prepared γ-La2S3: Ba2+ was 2.94 eV, which matched well with the experimental data. The energy band structure and density of states of the synthesized γ-La2S3: Ba2+ powder indicated that it was an indirect semiconductor which could be employed as a raw material for preparing infrared transparent optical ceramics.