Crystallographic Analysis and Structural Features of Honeycomb Cation Frameworks in Na 2 FePO 4 F, NaFePO 4 , and LiVOPO 4 Structures

The crystallographic analysis of the structures of compounds Na 2 FePO 4 F ( I ), NaFePO 4 ( II ), and LiVOPO 4 ( III ) reveals that there are vacant channels in “honeycomb” constructions of their cation frameworks. In these structures, the stability is based on a sequence of embedded (according to the “matryoshka” principle) pseudosymmetry-related pseudo-hexagonal configurations. Ordering of cation positions creates their configuration approaching highly symmetrical sublattices that are close in geometry to face-centered ( F cube ) and body-centered ( I cube ) cubic sublattices. The equivalent positions are occupied by different atoms and vacancies.