Synthesis of sodium nickel phosphate and its crystallographic, spectroscopic, and temperature-controlled X-ray diffraction study

Abstract

Sodium nickel phosphate NaNiPO4 has been synthesized by crystallization from salt solutions containing corresponding metals and phosphoric acid and subsequent heat treatment. NaNiPO4 with a maricite structure has been studied by a combination of methods. Its structure has been refined by the Rietweld method (space group Pnma, a = 8.7839(2) A, b = 6.7426(2), c = 5.0368(2) A, V = 298.31(2) A3, Z = 4). The structure framework is composed of edge-sharing NiO6 octahedra arranged in columns running along the b axis and linked with each other through PO4 tetrahedra. The cavities in the structure accommodate Na+ ions. No temperature-induced changes in the X-ray diffraction pattern of NaNiPO4 in the temperature range 25–700°C have been observed. The volumetric thermal expansion coefficient of the phosphate, αV = 34 × 10−6 K−1, allows one to classify it as a strongly expanding substance. Maricite structure stabilities are compared for NaEIIPO4 (EII = Mn, Fe, Co, Ni).