Na3(VO)(PO4)(CO3): a synthetic member of the bradleyite phosphate carbonate family with a new type of crystal structure

Abstract

The synthesis and characterization of a (VO)²⁺ representative in the bradleyite family of compounds is reported. The new trisodium vanadyl phosphate carbonate was investigated using scanning electron microscopy, microprobe analysis, low temperature X-ray diffraction, and theoretical calculations of possible pathways of Na migration through the framework. Its crystal structure is assembled from strongly distorted VO₆ octahedra, PO₄ tetrahedra, and triangular CO₃ groups linked into one-periodic ribbons parallel to the b axis of a monoclinic unit cell. Na atoms occupy positions between these ribbons and connect them into a framework. It is shown that the formal exchange of Fe²⁺ or Mn²⁺ for (VO)²⁺ ions leads to the bonshtedtite and sidorenkite crystal structure transformation from layered to chain ones. The character of the Na atom distribution in the structure allows considering Na₃(VO)(PO₄)(CO₃) as a potential electrochemically active material.