Effects of Mg3(PO4)2 addition on the crystal structure, mechanical and thermophysical properties of CaZr4P6O24 ceramics

Abstract

A novel series of CaZr4(PO4)6-x wt.% Mg3(PO4)2 (x = 0, 2, 4, 6, 8, and 10) ceramics was prepared via a co-precipitation method. The crystal structure, sintering characteristics, and mechanical and thermophysical properties of the Mg3(PO4)2 modified CaZr4(PO4)6 ceramics were investigated. All the samples possessed a pure CaZr4(PO4)6-type rhombohedral structure. The crystal structure analysed by Rietveld refinement revealed that the lattice parameter a increased, whereas c and the unit cell volume decreased with increasing Mg3(PO4)2. Meanwhile, the addition of Mg3(PO4)2 distorted the PO4 tetrahedron and ZrO6 octahedron. The sinterability was improved by increasing the Mg3(PO4)2 content, and the flexural strength and Vickers hardness monotonically increased to 74.5 MPa and 2.71 GPa, respectively. The thermal expansion varied from −2.27 to −0.37 × 10−6/°C with increasing Mg3(PO4)2 content. All compositions showed a low thermal conductivity, in the range of 0.44–0.56 W m−1 °C−1 from room temperature to 1000 °C. Near-zero thermal expansion combined with extraordinary mechanical properties provide ideal materials for low-thermal-expansion applications.