Symmetry-mode analysis for intuitive observation of structure-property relationships in the lead-free antiferroelectric (1-)AgNbO-LiTaO.

Functional materials are of critical importance to electronic and smart devices. A deep understanding of the structure-property relationship is essential for designing new materials. In this work, instead of utilizing conventional atomic coordinates, a symmetry-mode approach is successfully used to conduct structure refinement of the neutron powder diffraction data of (1-)AgNbO-LiTaO (0 ≤ ≤ 0.09) ceramics. This provides rich structural information that not only clarifies the controversial symmetry assigned to pure AgNbO but also explains well the detailed structural evolution of (1-)AgNbO-LiTaO (0 ≤ ≤ 0.09) ceramics, and builds a comprehensive and straightforward relationship between structural distortion and electrical properties. It is concluded that there are four relatively large-amplitude major modes that dominate the distorted 2 structure of pure AgNbO, namely a Λ3 antiferroelectric mode, a T4+ octahedral tilting mode, an H2 / octahedral tilting mode and a Γ4- ferroelectric mode. The H2 and Λ3 modes become progressively inactive with increasing and their destabilization is the driving force behind the composition-driven phase transition between the 2 and 3 phases. This structural variation is consistent with the trend observed in the measured temperature-dependent dielectric properties and polarization-electric field (-) hysteresis loops. The mode crystallography applied in this study provides a strategy for optimizing related properties by tuning the amplitudes of the corresponding modes in these novel AgNbO-based (anti)ferroelectric materials.