Characterization of Anion Disorder in Zirconate A ₂ B ₂ O ₇ Compounds by Raman Spectroscopy

Raman spectra were measured at room temperature and at liquid nitrogen temperature on six rare‐earth zirconates, RE 2 Zr 2 O 7 (RE=Nd, Sm, Gd, Dy, Er, and Yb). The spectra of the three compounds with large rare‐earth ions exhibited most of the expected Raman bands of the pyrochlore structure but with large, temperature‐independent half‐widths that could be related to the loss of translational symmetry imposed by incipient randomization of oxygen vacancies over two available anion sites. Compounds with the smaller rare‐earth ions have the fluorite structure, in which the disorder arises from the complete random distribution of seven oxygen ions over eight crystallographically equivalent sites. This degree of disorder reduces the Raman spectrum to a broad featureless density‐of‐states continuum.