Structural study of polymorphism and thermal behavior of CaZr(PO4)2

• Room temperature structure CaZr(PO4)2 was revised.
• A high temperature form of CaZr(PO4)2 was described for the first time.
• Thermal expansion of CaZr(PO4)2 was studied on the basis of the evolution of the crystal parameters evolution during heating.

The crystal structure of CaZr(PO4)2 has been revised by ab initio Rietveld analysis of X-ray powder diffraction data. At room temperature, CaZr(PO4)2 crystallizes in the orthorhombic space group Pna21 (Z = 4). Differential thermal analysis suggests a reversible second order transition at 1000 °C confirmed by high temperature XRD analysis that brings out the existence of a high temperature form, very similar to the room temperature one, but more symmetrical (Pnma, Z = 4). Analysis of the crystal parameters evolution during heating reveals that CaZr(PO4)2 exhibits a quite low thermal expansion coefficient of 6.11·10−6 K−1. This value stems from a combination of several mechanisms, including Coulombic repulsion and bridging oxygen rocking motion.

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