Giant dielectric tunability in ferroelectric ceramics with ultralow loss by ion substitution design

Due to their responsiveness to modulation by external direct current fields, dielectric tunable materials are extensively utilized in integrated components, such as ferroelectric phase shifters. Barium strontium titanate ceramics have been considered the most potential tunable materials for a long time. However, the significant dielectric loss and high voltage drive have limited their further applications. Recently, Bi₆Ti₅WO₂₂ ceramic has regained attention for its high dielectric tunability with low loss. In this study, we judiciously introduce Nb⁵⁺ with a larger ionic radius, replacing Ti⁴⁺ and W⁶⁺. This successful substitution enables the modulation of the phase transition temperature of Bi₆Ti₅WO₂₂ ceramics to room temperature, resulting in superior tunable properties. Specifically, the 0.7Bi₆Ti₅WO₂₂-0.3Bi₆Ti₄Nb₂O₂₂ ceramics exhibit giant tunability (~75.6%) with ultralow loss (<0.002) under a low electric field (1.5 kV/mm). This tunability is twice that of barium strontium titanate ceramics with a similar dielectric constant and only one-tenth of the loss. Neutron powder diffraction and transmission-electron-microscopy illustrate the nanodomains and micro-strains influenced by ion substitution. Density functional theory simulation calculations reveal the contribution of ion substitution to polarization. The research provides an ideal substitute for tunable material and a general strategy for adjusting phase transition temperature to improve dielectric properties.