The Ternary Yttrium Sulfides, CaY2S4, SrY2S4, and BaY2S4: Structures and Properties

X-ray single-crystal structure determinations have confirmed that CaY 2 S 4 crystallizes in the orthorhombic [Yb 3 S 4 ]-type structure whereas SrY 2 S 4 and BaY 2 S 4 adopt the orthorhombic [CaFe 2 O 4 ] structure. Both structure types feature three-dimensional frameworks built of edge- and corner-sharing [YS 6 ] octahedra. CaY 2 S 4 , in space group Pnma, has cell dimensions a = 12.953(3) A, b = 3.8835(5)A, c = 13.081(3)A, Vol = 658.0(2)A 3 , Z = 4, and D x = 3.494 g/cm 3 (M F = 346.1). SrY 2 S 4 , in Pmnb, has a = 3.9775(6), b = 11.974(2), c = 14.294(2)A, Vol = 680.8(2)A 3 , Z = 4, and D x = 3.841 g/cm 3 for M F = 393.7; BaY 2 S 4 , in Pmnb, has a = 4.0263(2), b = 12.2134(8), c = 14.484(1)A, Vol = 712.23(9) A 3 , Z = 4, and D x = 4.135 g/cm 3 for M F = 443.4. Room temperature X-ray powder diffraction data for all three compounds and high-temperature unit cells for CaY 2 S 4 are also reported. The overall average linear thermal expansion of CaY 2 S 4 upon heating was found to be approximately 11.9 x 10 -6 /°K as compared to that of 7.2 x 10 -6 /°K found for ZnS. The onset oxidative decomposition temperatures for CaY 2 S 4 , SrY 2 S 4 , and BaY 2 S 4 were observed to be 545, 565, and 590°C, respectively, as compared to 530°C for ZnS. The properties of these compounds indicate that they are potentially useful as infrared window materials.