Investigation and characterization of crystal structure, mechanical and thermophysical properties of CaZr4-xTixP6O24 ceramics

Abstract A novel series of CaZr 4-x Ti x P 6 O 24 ceramics based on sodium zirconium phosphate was prepared by the co-precipitation method. The effects of Ti 4+ substitution for Zr 4+ on the crystal structure, sintering characteristics, Raman spectra, and mechanical and thermophysical properties were examined. X-ray diffraction results indicated that all compositions exhibited a single phase with a rhombohedral structure. The Raman spectra revealed no significant changes with increasing Ti 4+ content. The crystal structure was analysed by Rietveld refinement, and the lattice parameters were obtained with a satisfactory structural convergence of R-factors. Ti 4+ substitution could effectively improve sinterability and reduce microcracks via decrease of the c/ a ratio. The flexural strength and Vickers hardness monotonically increased to 58.63 MPa and 2.73 GPa, respectively. The thermal expansion coefficient varied from −2.14 to −0.87 × 10 −6 /°C with increasing Ti 4+ content, suggesting a tendency towards zero thermal expansion. In addition, all compositions showed low thermal conductivity, approximately 0.56–0.99 W m −1  °C −1  at 1000 °C. The results indicated that the extraordinary mechanical and thermophysical properties of CaZr 4-x Ti x P 6 O 24 ceramics may have great potential in high-temperature applications.