DSC, structural single crystal and X-ray powder diffraction study of the ammonium sulfate selenate tellurate mixed solid solution

Crystal structure of (NH4)2(SO4)0.73(SeO4)0.27Te(OH)6 (NSSeTe) crystallizes in the monoclinic P21/c space group. It was analyzed at room temperature using X-ray diffractometer data. The unit cell parameters are a = 13.7340(2) A, b = 6.6583(1) A, c = 11.4582(2) A, β = 106.8270(6)o, Z = 2, V = 1002.93(3) A3, R = 0.014, Rw = 0.017 and Dx = 2.426 g cm-3. The main feature of this atomic arrangements is the coexistence of three and different anions (SO42-, TeO66- and SeO42- groups) in the unit cell, connected by hydrogen bonds which make the building of the crystal. The distribution of atoms can be described as isolated TeO6 octahedra and SO4 and/or SeO4 tetrahedra occupying the same positions. The NH4+ cations, are located between these polyhedra. The molecular species present in the lattice are S/SeO42- tetrahedra and TeO66- octahedra disposed in a number of sheets. The thermal analysis of the title compound show three distinct endothermal peaks at 398, 430 and 450 K. X-ray powder diffraction data at different temperatures confirm that the first anomaly at 398 K can be attributed to a structural phase transition