Synthesis, structure, and thermal expansion of sodium zirconium arsenate phosphates

Sodium zirconium arsenate phosphates NaZr2(AsO4) x (PO4)3−x were synthesized by precipitation technique and studied by X-ray diffraction and IR spectroscopy. In the series of NaZr2(AsO4) x (PO4)3−x , continuous substitution solid solutions are formed (0 ≤ x ≤ 3) with the mineral kosnarite structure. The crystal structure of NaZr2(AsO4)1.5(PO4)1.5 was refined by full-profile analysis: space group R 3 c, a = 8.9600(4)Å, c = 22.9770(9) Å, V = 1597.5(1) Å3, R wp = 4.55. The thermal expansion of the arsenate-phosphate NaZr2(AsO4)1.5(PO4)1.5 and the arsenate NaZr2(AsO4)3 was studied by thermal X-ray diffraction in the temperature range of 20–800°C. The average linear thermal expansion coefficients (αav = 2.45 × 10−6 and 3.91 × 10−6 K−1, respectively) indicate that these salts are medium expansion compounds.