Synthesis and X-ray crystallographic and IR spectroscopic study of complex alkaline earth zirconium arsenates

Resumo

Arsenates A_0.5Zr₂(AsO₄)₃ (A = Mg, Ca, Sr, Ba), synthesized through sol–gel route with subsequent heat treatment, have been studied by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Mg_0.5Zr₂(AsO₄)₃ crystallizes in the Sc₂(WO₄)₃ structure type (space group P2₁/n). A_0.5Zr₂(AsO₄)₃ (A = Ca, Sr, Ba) crystallize in the NaZr₂(PO₄)₃ structure type (space group \(R\bar 3\)). The Ca_0.5Zr₂(AsO₄)₃ and Ba_0.5Zr₂(AsO₄)₃ structures have been refined by the full-profile analysis. The structure frameworks are composed of ZrO₆ octahedra and AsO₄ tetrahedra. The alkaline earth metal atoms occupy one of the two extraframework positions inside the structure columns. The internal vibrational frequencies of the AsO₄^3- tetrahedron have been assigned. The number of the observed bands corresponds to the number predicted by the factor group analysis of vibrations for space groups \(R\bar 3\) and P2₁/n.