Abstract
Barium lanthanum ternary sulfide (compositions within the BaLa(2)S(4)- γ-La(2)S(3) solid solution of cubic Th(3)P(4)-type structure, referred to as BLS) was investigated as a novel infrared transparent ceramic for applications as external structural window material. This research marks the initial efforts to consolidate BLS powders into dense ceramics and reports, for the first time, the processing of polycrystalline BLS infrared transparent ceramics. The powders were produced through a combustion synthesis method followed by a sulfurization treatment in pure H(2)S. Sintering was carried out using hot-pressing and natural sintering. The characteristics of the powders and ceramics (purity, morphology, microstructure and optical transmission) are detailed and compared to evaluate the effectiveness of the two sintering techniques. A peak transmission of 20% at 16.5 μm was achieved for 1.4 mm-thick ceramics that were hot-pressed for 2 h at 1250 °C and subsequently annealed for 12 h at 1250 °C in pure H(2)S. With an extended transparency window (up to 20 μm, compared with 12 μm for ZnS), BLS polycrystalline ceramics are uniquely suited for use in harsh environments for space applications in both civil and military fields. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-025-22356-w.