X-ray powder diffraction, vibration and thermal studies of [A0.92(NH4)0.08]2TeCl4Br2 with Axa0;=xa0;Cs, Rb: Influence of mixed cationic and anionic substitutions
摘要
The crystal structures of [A0.92(NH4)0.08]2TeCl4Br2 with AxA0;=xA0;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: axA0;=xA0;7.452(1)xA0;脜, cxA0;=xA0;10.544(3)xA0;脜, ZxA0;=xA0;2 and axA0;=xA0;7.315(2)xA0;脜, cxA0;=xA0;10.354(4)xA0;脜, ZxA0;=xA0;2 in the presence of Cs and Rb, respectively. These two compounds have an antifluorite-type arrangement of NH4+/Rb+/Cs+ and octahedral TeCl4Br22鈭?/sup> anions. The stability of these structure is by ionic and hydrogen bonding contacts: A鈰疌l, A鈰疊r and N-H鈰疌l, N-H鈰疊r. The different vibrational modes of these powders were analysed by FTIR and Raman spectroscopic studies. A DTA/TGA experiment reveals one endothermic peak at 780xA0;K implicating the decomposition of the sample. At low temperature, one endothermic peak in thermal behavior is detected at around 213xA0;K by DSC experiment. This transition was confirmed by dielectric measurements.