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

Abstract Crystal structure of (NH 4 ) 2 (SO 4 ) 0.73 (SeO 4 ) 0.27 Te(OH) 6 (NSSeTe) crystallizes in the monoclinic P 2 1 / 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)°, Z  = 2, V  = 1002.93(3) A 3 , R  = 0.014, R w  = 0.017 and D x  = 2.426 g cm −3 . The main feature of this atomic arrangements is the coexistence of three and different anions (SO 4 2− , TeO 6 6− and SeO 4 2− 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 TeO 6 octahedra and SO 4 and/or SeO 4 tetrahedra occupying the same positions. The NH 4 + cations, are located between these polyhedra. The molecular species present in the lattice are S/SeO 4 2− tetrahedra and TeO 6 6− 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.