Phosphates of pentavalent elements: Structure and properties

Abstract

Possible formula types of orthophosphate octahedron-tetrahedron frameworks {[T2(PO4)3]n−}3∞ (where T2 are elements in identical or different oxidation states +1, +2, +3, +4, and +5) have been calculated and described. The data on the structure and properties of well-known phosphates with mixed frameworks of such a type containing elements in the oxidation state +5 are systematized. Most are crystallized in the structure type NaZr2(PO4)3 (NZP). For these phosphates, the relative differences in the radii of framework-forming cations do not exceed 0.6. It is shown that NZP-like compounds with the expected structure and specified properties can be modeled by phosphates with electrically neutral frameworks. The model predictions were justified by synthesis and crystallographic investigations of niobium phosphates with bi-and trivalent elements.