Structure and thermal expansion of KGe2(PO4)3

KGe2(PO4)3 has been prepared in both crystalline and vitreous forms. The NZP-type structure of the crystalline variety and its thermal expansion have been investigated by X-ray powder diffraction. The crystal structure has been refined by the Rietveld method in the space group R3̄. The thermal expansion coefficients have been determined between room temperature and 600 °C and compared to dilatometry measurements. The parameters a and c have a positive and isotropic behavior and the average macroscopic thermal expansion coefficient, <α>, is 10 × 10−6 ° C−1 at 600 °C. A comparison with the thermal expansion of the related Li and Na compounds is reported.