Thermal expansion of NZP-family alkali-metal (Na, K) zirconium phosphates

• Published in: Inorganic materials 2000-08, Vol.36 (8), p.830-834
• Main Authors: Orlova, A. I., Kemenov, D. V., Samoilov, S. G., Kazantsev, G. N., Pet’kov, V. I.
• Format: Article
• Language: English
• Subjects: Anisotropy; High temperature; Phosphates; Sodium zirconium phosphate; Thermal expansion; X ray powder diffraction
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1007/BF02758606

The thermal expansion of the AxZr2.25-0.25x(PO4)3 phosphates with A = Na(x = 0.5,1.0,2.0,3.0,4.0, 5.0) and K(x = 1.0, 3.0, 5.0), crystallizing in structures of the NaZr2(PO4)3 type (sp. gr.R3c or C2/c), was studied by high-temperature x-ray powder diffraction in the range 20–700‡C. The lattice parametersa and c and thea- andc-axis thermal expansion coefficients (αa and αc) were determined. The thermal expansion of the phosphates was found to be highly anisotropic (αa < 0, αc > 0). The strongest anisotropy was found in NaZr2(PO4)3 (αa = -4.89 x 10-6 K-1, αc = 22.02 x 10-6 K-1), KZr2(PO4)3 (αa =-5.30 x 10-6 K-1, αc = 5.41 x 10-6 K-1), and Na5Zr(PO4)3 (αa = -5.82 x 10-6 K-1, αc= 20.73 x 10-6 K-1). K5Zr(PO4)3 exhibited the smallest thermal expansion and weak anisotropy (αa = -2.14 x 10-6 K-1, αc = 2.65 x 10-6 K-1). The effects of M(l) and M(2) site occupancies on αa, αc,a, and c were assessed. The relative magnitudes of crystal-chemical and thermal expansion in the Na and K compounds were analyzed.