Synthesis and study of Cd0.5 + xMxZr2‒x(PO4)3 (M = Mg, Co, Mn) phosphates

Abstract

New phosphates Cd_{0.5 + x}M_xZr_2‒x(PO₄)₃ (M = Mg, Co, Mn) have been prepared by sol–gel method. The formation of limited solid solutions Cd_{0.5 + x}M_xZr_2‒x(PO₄)₃ of the NaZr₂(PO₄)₃ (NZP) structural type, 0 ≤ x ≤ 0.6 for М = Mg and 0 ≤ х ≤ 0.3 for M = Co and Mn, has been found using X-ray diffraction, IR spectroscopy, and electron microprobe analysis. The distribution of cations in the 2+ oxidation state over crystallographic positions of the NZP structure has been shown in the phosphate CdMg_0.5Zr_1.5(PO₄)₃. It has been found that half of framework-forming octahedral positions in the structure of the latter are occupied by Zr4+ cations and the other half are randomly occupied by Zr⁴⁺ and Cd²⁺ ions. The Cd²⁺ and Mg²⁺ ions alternately occupy the positions of structure cavities. The thermal expansion of CdMg_0.5Zr_1.5(PO₄)₃ in a temperature range of 25‒800°C has been studied. The phosphate is found to be among the medium expanding substances.