Investigating the Local Structure of Lanthanoid Hafnates Ln₂Hf₂O₇ via Diffraction and Spectroscopy

Abstract

The lanthanoid hafnates Ln2Hf2O7 (Ln = La, Pr, Nd, Sm–Tm) were studied using a combination of synchrotron X-ray and neutron powder diffraction together with X-ray absorption and Raman spectroscopy. Spectroscopic methods revealed a gradual increase in disorder from the ideal pyrochlore structure to the defect fluorite structure as the size of the Ln cation increases. The line shape of the Hf L3-edge X-ray absorption near edge spectra which is sensitive to the local coordination environment changed with increasing disorder. The general line shape of the O K-edge XANES and Raman spectra also indicated an increase in disorder across the Ln2Hf2O7 series. Differences in the diffraction and spectroscopy analysis reflect the greater sensitivity of the spectroscopy techniques to local ordering.