Evidence for Local Structural Distortion and Mixed States of Fe in β-NaFeO2: A Bond Valence Sum Analysis

Abstract

We have analyzed the crystal structure, interatomic distances and bond valence sums in β-phase of sodium ferrite based on neutron diffraction measurement at room temperature. The Rietveld analysis performed using Pna21 space group obtains smaller lattice constants compared to the previous reports. This discrepancy is attributed to the sodium deficiency. We notice that the Na-O bonds are shortened, while Fe-O bonds are elongated. The calculated bond valence sum around the sodium and the iron ions are 1.08 and 2.64, respectively. This indicates the presence of Fe2+-Fe3+ mixed valence state.