Phosphates ZnxMg0.5 +xE2 –x(PO4)3 (E = Ti, Zr): Synthesis, Structural Characteristics, and Thermal Expansion

Resumo

Phosphates Zn_xMg_0.5 + xE_2 – x(PO₄)₃ (E = Ti, Zr) have been synthesized by the sol-gel method with further thermal treatment and studied by X-ray diffraction, electron microprobe analysis, and IR spectroscopy. It has been established that the Zn_xMg_0.5 + xTi_2 – x(PO₄)₃ solid solution (0 ≤ х ≤ 0.5, space group R\(\bar {3}\)) crystallizes in the NaZr₂(PO₄)₃ structural type and is stable up to 1050°C. The structure of Zn_0.2Mg_0.7Ti_1.8(PO₄)₃ has been refined. It is based on the framework of PO₄ tetrahedra with shared apices and (Mg,Ti)O₆ octahedra. The framework cavities accommodate Mg²⁺ and Zn²⁺ cations with octahedral oxygen coordination. The Zn_xMg_0.5 + xZr_2 – x(PO₄)₃ solid solution (0 ≤ х ≤ 0.5, space group P2₁/n) crystallizing in the Sc₂(WO₄)₃ structural type is thermally unstable above 1000°C. The number of bands for the stretching and bending vibrations of the \({\text{PO}}_{4}^{{3 - }}\) ion in the IR spectra of these orthophosphates agrees with the group factor analysis for space groups R\(\bar {3}\) and P2₁/n. The thermal expansion of the Zn_xMg_0.5 + xE_2 – x(PO₄)₃ solid solutions has been studied within a temperature range of 25–800°C. The control over the composition of these moderately and highly expansive materials provides the possibility to change the thermal expansion characteristics in the desired direction.