Synthesis, Structure and Thermophysical Properties of Phosphates MNi0.5Zr1.5(PO4)3 (M = Mg, Ca, Sr)

New phosphates MNi0.5Zr1.5(PO4)3 (M = Mg, Ca, Sr) were prepared by the precipitating method. Phosphates were characterized using X-ray powder diffraction, IR-spectroscopy and electron microprobe analyses. The crystal structure of phosphates was refined by the Rietveld method. Phosphates CaNi0.5Zr1.5(PO4)3 and SrNi0.5Zr1.5(PO4)3 are shown to have been crystallized in the NaZr2(PO4)3-type structure and the phosphate MgNi0.5Zr1.5(PO4)3 was obtained as a single-phase with Sc2(WO4)3-type structure. Heat capacity of phosphate CaNi0.5Zr1.5(PO4)3 was measured in the range 7 – 650 K and increased monotonically over the entire temperature range studied. Thermal expansion of phosphate CaNi0.5Zr1.5(PO4)3 was studied in the interval 295-1073 K by the high temperature X-ray diffraction. This phosphate is similar to the best low-expansion ceramics, such as zircon, cordierite and silica glass in thermal expansion behavior