Rare-earth titanate pyrochlores have attracted significant attention for their unique magnetic frustration; however, research on the origin of low-temperature dielectric dispersion and the relationship between dielectric properties and structure lags far behind. Here, by systematically investigating the dielectric properties of representative rare-earth titanates R2Ti2O7 (R = La, Nd, Sm, Er, Yb, and Lu), we demonstrate that R2Ti2O7 with a cubic pyrochlore structure exhibits low-temperature dielectric dispersion behavior, while the other compounds with a monoclinic perovskite-like layered structure possess no dispersion behavior but excellent temperature-stable dielectric property. The dielectric dispersion in cubic pyrochlores arises from the structural distortion. Furthermore, the existence of structural distortion is affirmed by the anomalous phonon softening of A1g Raman mode around the dielectric dispersion temperature, and the origin of the structural distortion is attributed to anharmonic phonon–phonon interactions induced by intrinsic vacant oxygen at Wyckoff 8a sites. In addition, with increasing ionic radius from R = Lu to Sm, the increased lattice parameter leads to varied bond length and bond angle of Ti-O(1)-Ti, which strengthens the local lattice distortion of TiO(1)6 octahedra and thus enhances diffusion degree of dielectric dispersion. On the other hand, the absence of intrinsic vacant oxygen site hardly gives rise to the local structural distortion and thus no dielectric dispersion in monoclinic R2Ti2O7. Our work not only clarifies the mechanism of dielectric dispersion but also gives a comprehensive perspective on the structure–property relationship of rare-earth titanates R2Ti2O7, and thus lays a solid foundation for further work on related materials.

中文翻译：

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结构畸变诱导的低温介电分散在镧系钛酸盐焦绿石中的作用


稀土钛酸焦绿石因其独特的磁阻而引起了广泛关注;然而，关于低温介电色散的起源以及介电性能与结构之间关系的研究远远落后。在这里，通过系统研究代表性稀土钛酸盐 R2Ti2O7 （R = La、Nd、Sm、Er、Yb 和 Lu） 的介电特性，我们证明了具有立方焦绿石结构的 R2Ti2O7 表现出低温介电分散行为，而其他具有单斜钙钛矿状层状结构的化合物没有分散行为，但具有出色的温度稳定介电性能。立方焦绿石中的介电色散是由结构变形引起的。此外，A1g 拉曼模式在介电色散温度附近的异常声子软化证实了结构失真的存在，结构失真的起源归因于 Wyckoff 8a 位点的本征空氧诱导的不谐声子-声子相互作用。此外，随着离子半径从 R = Lu 增加到 Sm，晶格参数的增加导致 Ti-O（1）-Ti 的键长和键角发生变化，从而加强了 TiO（1）6 八面体的局部晶格畸变，从而提高了介电色散的扩散程度。另一方面，缺乏本征空氧位点几乎不会引起局部结构畸变，因此在单斜 R2Ti2O7 中没有介电色散。我们的工作不仅阐明了介电色散的机理，而且对稀土钛酸盐 R2Ti2O7 的结构-性能关系给出了全面的视角，从而为相关材料的进一步工作奠定了坚实的基础。