Syntheses, crystal and electronic structures of compounds AM(PO4)(2) (A = Sr, M = Ti, Sn; A = Ba, M = Sn)

Three ternary metal diorthophosphates (V), AM(PO4)(2) (A = Sr, M = Ti, Sn; A = Ba, M = Sn), have been prepared by high-temperature solution growth (HTSG) method and structurally characterized by single-crystal X-ray diffraction analysis for the first time. The structure of BaSn(PO4)(2) features the yavapaiite-type structure, with space group C2/m and a = 8.214(2), b = 5.2456(13), c = 7.8938(19) angstrom, beta = 94.561(4)degrees, Z = 2, R-1 (all data) = 0.0253. Compounds SrM(PO4)(2) (M = Ti, Sn) are isostructural and crystallize in a novel distorted yavapaiite structure, with space group C2/c and a = 16.4617(4), b = 5.1720(3), c = 8.1187(2) angstrom, beta = 116.40(2)degrees, Z = 4, R-1 (all data) = 0.016 for SrTi(PO4)(2); a = 16.674(14), b = 5.223(4), c = 8.099(6) angstrom, beta = 115.821(11)degrees, Z = 4, R-1 (all data) = 0.025 for SrSn(PO4)(2). Band structure calculations from the density functional theory (DFT) method indicate that all three compounds are approximately direct band-gap insulators.