Apr 20th, 1:00 PM - 4:00 PM
Crystallographic Characterization of Rare-Earth Hafnates
The nature and degree of disorder in the Ln2Hf2O7 (Ln = La → Lu) series has never been fully quantified. The purpose of this study is to investigate the cstructure of such pyrohafnates and specifically to determine the degree of both cation and anion disorder, both of which have implications for ionic conductivity. Towards that end, several lanthanide pyrohafnate ompounds, Ln2Hf2O7 (Ln = La, Pr, Nd, Tb, Dy, Yb, and Lu), have been synthesized via a solid-state reaction mechanism. The crystal structures were determined by electron diffraction, and Rietveld structural refinements were conducted using neutron diffraction data collected at the Los Alamos Neutron Science Center. As expected, low-Z lanthanides result in pyrochloric compounds whereas high-Z lanthanides form fully fluoritic ones. Intermediate lanthanides form partially disordered pyrochlores, and some show anionic disorder unconnected to cation disorder. As expected, the fluorite-equivalent cubic lattice constant was found to decrease as Z increases.