THERMAL-EXPANSION AND CRYSTAL-CHEMISTRY OF (SR-1-X,K-2X)ZR-4(PO4)(6) CERAMIC

Thermal expansion of (Sr-1-x, K-2x)Zr-4(PO4)(6) (SrKZP) (with x = 0-1) ceramic was investigated using both a dilatometer and a high-temperature X-ray diffractometer. The coefficients of thermal expansion (CTEs) of the SrKZP ceramic measured by the dilatometer demonstrate a similar trend as those from high-temperature X-ray diffraction. Both measurements show an ultra-low CTE at x = 0.5; nevertheless, this composition shows significant lattice thermal-expansion anisotropy (TEA), while the minimum TEA appears with composition x = 0.2. Although it possessed a sufficient degree of TEA, the x = 0.5 composition showed no visible microcracks or negligible microcracks over a grain size as large as 15 mu m. A transition of space group from R (3) over bar to R (3) over bar c with composition between x = 0.3 and x = 0.5 has been observed. The crystal structure of the SrKZP ceramic with possible occupations of strontium and/or potassium within the lattice in relation to their influence on the CTEs is proposed.