Structural distortion-induced low-temperature dielectric dispersion in lanthanide titanate pyrochlores.

This article focuses on the relationship between crystal structure and low-temperature dielectric dispersion in rare-earth titanates R₂Ti₂O₇, where R is a trivalent rare-earth cation (La, Nd, Sm, Er, Yb, Lu). It demonstrates that compounds with a cubic pyrochlore structure (R = Sm, Er, Yb, Lu) exhibit low-temperature dielectric dispersion due to local structural distortion, while those with a monoclinic perovskite-like layered structure (R = La, Nd) show no such dispersion and possess temperature-stable dielectric properties. The structural distortion in cubic pyrochlores is linked to anharmonic phonon–phonon interactions induced by intrinsic oxygen vacancies at Wyckoff 8a sites, as supported by anomalous phonon softening observed in temperature-dependent Raman spectra. This work clarifies the mechanism behind dielectric dispersion and provides insight into the structure–property relationships in rare-earth titanates.