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

Abstract

A novel series of CaZr4-xTixP6O24 ceramics based on sodium zirconium phosphate was prepared by the co-precipitation method. The effects of Ti4+ substitution for Zr4+ 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 Ti4+ content. The crystal structure was analysed by Rietveld refinement, and the lattice parameters were obtained with a satisfactory structural convergence of R-factors. Ti4+ 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 Ti4+ 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 CaZr4-xTixP6O24 ceramics may have great potential in high-temperature applications.