X-ray powder diffraction, vibration and thermal studies of [A0.92(NH4)0.08]2TeCl4Br2 with A = Cs, Rb: Influence of mixed cationic and anionic substitutions

The crystal structures of [A0.92(NH4)0.08]2TeCl4Br2 with A = Cs, Rb have been determined using X-ray powder diffraction techniques. The two compounds crystallize in the tetragonal space group P4/mnc, with the unit cell parameters: a = 7.452(1) Å, c = 10.544(3) Å, Z = 2 and a = 7.315(2) Å, c = 10.354(4) Å, Z = 2 in the presence of Cs and Rb, respectively. These two compounds have an antifluorite-type arrangement of NH4+/Rb+/Cs+ and octahedral TeCl4Br22− anions. The stability of these structure is by ionic and hydrogen bonding contacts: A⋯Cl, A⋯Br and N–H⋯Cl, N–H⋯Br. The different vibrational modes of these powders were analysed by FTIR and Raman spectroscopic studies. A DTA/TGA experiment reveals one endothermic peak at 780 K implicating the decomposition of the sample. At low temperature, one endothermic peak in thermal behavior is detected at around 213 K by DSC experiment. This transition was confirmed by dielectric measurements.