Transmission Electron Microscopic Study of Pyrochlore to Defect-Fluorite Transition in Rare-Earth Pyrohafnates

Authors

Chinnathambi Karthik, Boise State UniversityFollow
Thomas Anderson, Boise State University
Delphine Gout, Oak Ridge National Laboratory
Rick Ubic, Boise State UniversityFollow

Document Type

Article

Publication Date

10-1-2012

Abstract

A structural transition in rare earth pyrohafnates, Ln₂Hf₂O₇ (Ln=Y, La, Pr, Nd, Tb, Dy, Yb and Lu), has been identified. Neutron diffraction showed that the structure transforms from well-ordered pyrochloric to fully fluoritic through the lanthanide series from La to Lu with a corresponding increase in the position parameter x of the 48f (Fdm) oxygen site from 0.330 to 0.375. As evidenced by the selected area electron diffraction, La₂Hf₂O₇, Pr₂Hf₂O₇ and Nd₂Hf₂O₇ exhibited a well-ordered pyrocholoric structure with the presence of intense superlattice spots, which became weak and diffuse (in Dy₂Hf₂O₇ and Tb₂Hf₂O₇) before disappearing completely as the series progressed towards the Lu end. High resolution electron microscopic studies showed the breakdown of the pyrochlore ordering in the form of antiphase domains resulting in diffused smoke-like superlattice spots in the case of Dy₂Hf₂O₇ and Tb₂Hf₂O₇.

Publication Information

Karthik, Chinnathambi; Anderson, Thomas; Gout, Delphine; and Ubic, Rick. (2012). "Transmission Electron Microscopic Study of Pyrochlore to Defect-Fluorite Transition in Rare-Earth Pyrohafnates". Journal of Solid State Chemistry, 194168-172. https://doi.org/10.1016/j.jssc.2012.05.008