Connecting dielectric response to dominant vibrations and tolerance factors in pyrochlore oxides

Abstract

Dielectric screening originating from electronic and vibrational degrees of freedom is a fundamental material’s property. This property is crucial for materials used as high K-gate dielectric with metal gates in field-effect transistors in integrated circuits. Therefore, we atomically explore phonons responsible for dielectric screening in rare-earth pyrochlores zirconate oxides, RE2Zr2O6O’ (RE = Pr, Nd, Sm, Eu, and Gd), and suggest pathways for engineering the dielectric response for better dielectric insulators. The predicted crystal structures are close to the ideal pyrochlore structure but show a tendency towards the fluorite structure along the family (which alters dielectric screening). A significant contribution towards the dielectric screening originates from the infrared-active vibration (F1u named as m2) near 125 cm−1, which is mainly due to O’-RE-O’ bend. The vibration near 200 cm−1 also has notable contribution but shows a gradual decrease along the family. A relation between tolerance factors (t1 and t2) of pyrochlores and dielectric response is developed for the first time. Specifically, a linear relation of t2 with dominating vibration (m2) contributing to the dielectric constant paves the way to engineer the dielectric screening by a simple calculation of the tolerance factor in pyrochlore zirconates.