Structure and thermal behaviour of Sr-doped (NH4)2TeBr6 material

The crystal structure of the new Sr-doped material Sr0.02(NH4)1.98TeBr6, has been investigated using X-ray single crystal analysis at room temperature. The space group is Fm3¯m with lattice parameter a = 10.7136(2) Å and Z = 4. The refinement converged to R(F) = 0.017 and WR2 = 0.036. This compound belongs to antifluorite K2[PtCl6] family. The main structure of this material is based on TeBr62− regular octahedron. Sr2+ ions replace at random and in the same site the NH4+ ions within the structure of the undoped compound, (NH4)2TeBr6. The mixture of Sr2+/NH4+ cations are located between the TeBr62− octahedral ensuring the stability of the structure by ionic and hydrogen bonding contacts N-H…Br. By comparison with (NH4)2TeBr6 the Sr-doping does not affect the structural arrangement, but it leads to decrease the cubic lattice cell dimensions and the Te-Br distances and gives more disorder of NH4+ groups. The presence of the ammonium groups was confirmed using the infrared spectroscopy.