Synthesis, Crystal Structure, and Thermal Expansion of Sodium Barium Zirconium Phosphate–Sulfate

Abstract

The phosphate–sulfate synthesis approach preventing the elimination of sulfur in the process of synthesis has been tested for NaBa₆Zr(PO₄)₅SO₄ as an example. The phase formation and thermal stability of phosphate–sulfate have been studied by X-ray diffraction and DTA-TG. The NaBa₆Zr(PO₄)₅SO₄ structure (space group I\(\overline 4 \)3d, a = 10.5449(3) Å, V = 1172.54(5) ų, Z = 4) allied to the eulytite mineral has been refined by the Rietveld method. The structure is formed by wavy chains of edge-sharing (Na,Ba,Zr)O₆-octahedra and (P,S)O₄-tetrahedra sharing apices with the octahedra. Using thermal X-ray diffraction, it has been established that phosphate–sulfate is a strongly expanding material (α_а = α_b = α_c = 13.3 × 10^–6°C^–1).