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

Abstract

The lanthanoid hafnates Ln 2 Hf 2 O 7 (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 L 3 -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 Ln 2 Hf 2 O 7 series. Differences in the diffraction and spectroscopy analysis reflect the greater sensitivity of the spectroscopy techniques to local ordering.