Sodium Cerium Phosphate, (Na,Ce)₂Ce(PO₄)₂ ⋅ xH₂O, with Mixed Cerium Oxidation States

Abstract

A previously unknown double ceric sodium phosphate hydrate Na1.97Ce1.03(PO4)2 ⋅ xH2O containing both ceric and cerous cations was obtained by the hydrothermal treatment of amorphous ceric phosphate mixed with a sodium hydroxide aqueous solution. The presence of Ce3+ in the structure was proved by HERFD‐XANES and ESR spectroscopy. Iterative transformation factor analysis of HERFD‐XANES data allowed estimating the content of Ce3+ as 10 % of the total cerium. Water content of x=0.55 has been determined by thermogravimetric analysis combined with mass‐spectrometry data. The structure of the compound was solved from powder X‐ray diffraction data (S.G. P21/c a=6.9441(2) Å, b=11.6805(3) Å, c=9.3434(3) Å, β=111.6827(18)°). The new ceric sodium phosphate hydrate has a tunnel structure, where Ce3+ cations most likely partially occupy Na+ positions. The crystal structure of the novel compound has no direct analogues among the crystal structures of double tetravalent metal phosphates.