Obtaining and comparing the electron densities of (anti-)ferroelectric alkali niobates via x-ray diffraction

The electronic origin of antiferroelectricity is considered not fully understood by most of the scientific community. Sodium niobate evolves from a paraelectric cubic to an antiferroelectric orthorhombic structure via a series of phonon instabilities. A combination of Rietveld refinement and Maximum Entropy Method is employed to gain insight into the differences between ferroelectrics and antiferroelectrics with respect to their electron density. Using this technique, the electron density distributions of room temperature LiNbO₃, NaNbO₃ and KNbO₃ have been calculated from powder diffraction experiments to study the extent to which the Nb-O hybridization changes the electron distribution from the ionic bonding originally proposed for the cubic structures of these perovskites. This study investigates the character of the Nb-O bonds as well as the A site cation environment and proves that the Rietveld + MEM approach is not limited to synchrotron radiation data, making it much more commonly available.