Investigation of zirconium phosphate Zr₃(PO₄)₄ during heating

Abstract

Zirconium phosphate Zr₃(PO₄)₄ has been synthesized by the sol-gel technique and investigated using X-ray powder diffraction, IR spectroscopy, and differential scanning calorimetry. It has been established that the symmetry of the unit cell, R $\bar 3$ c, which is characteristic of the NaZr₂(PO₄)₃ (NZP) family, is lowered to P $\bar 3$ c. The behavior of the zirconium phosphate during heating has been examined using high-temperature X-ray diffraction at temperatures ranging from 25 to 575°C. It has been revealed that the structure of the zirconium phosphate is hardly subjected to expansion due to heating in the temperature ranges 25–125°C (α _a < 1 × 10⁻⁶ K⁻¹, α _c < 1 × 10⁻⁶ K⁻¹, Δα < 1 × 10⁻⁶ K⁻¹) and 325–575°C (α _a = −1.4 × 10⁻⁶ K⁻¹, α _c < 1 × 10⁻⁶ K⁻¹, Δα < −2.4 × 10⁻⁶ K⁻¹). In the temperature range 125–325°C, the synthesized compound undergoes a second-order phase transition (upon heating), which is accompanied by the contraction of the structure along all crystallographic directions. Upon cooling in the range from 75 to 25°C, the phase transition is accompanied by the expansion of the structure.