Synthesis, Structure, IR-Spectroscopic Characterization, and Ionic Conductivity of Mg0.5Zr2(AsO4)x(PO4)3 − x

Abstract

Mg_0.5Zr₂(AsO₄)_x(PO₄)_{3 − x} arsenate phosphates have been prepared by a sol–gel process and characterized by X-ray diffraction, IR spectroscopy, and impedance spectroscopy. The results indicate the formation of a continuous series of solid solutions with the Sc₂(WO₄)₃ structure (sp. gr. P2_1/n) in the composition range 0 < x < 3. The unit-cell parameters of the solid solutions increase linearly with composition, as a consequence of arsenic substitution for phosphorus, which has a smaller ionic radius. The number of observed stretching and bending bands of the AsO₄^3- and PO₄^3- ions in the IR spectra of the solid solutions agrees with that predicted by factor group analysis for space group P2_1/n. The observed gradual shift of the absorption bands of the AsO₄ tetrahedra to lower frequencies with increasing arsenic content on the tetrahedral site supports the X-ray diffraction evidence of the formation of substitutional solid solutions. The cation conductivity of Mg_0.5Zr₂(AsO₄)_x(PO₄)_{3 − x} with 0 ≤ х ≤ 1 has been shown to exceed the conductivity of the parent magnesium zirconium arsenate.