Unraveling the discrepancy of temperature- and composition-dependent strain regulation in Bi0.5Na0.5TiO3 ceramics

Abstract

For Bi0.5Na0.5TiO3 (BNT)-based materials, regulating temperature and composition could both induce giant electro-strain under the critical condition. Nevertheless, only the temperature-dependent regulation method achieved low hysteresis and maintained a high strain under high ergodic condition simultaneously. Herein, we investigated the origin of this discrepancy by means of matrix with close strain level. These two regulation methods exhibited different regulation mechanisms, especially for the microscopic structure (i.e., the discrepant lattice structure and polar entities). The A-site and BO6 octahedral-dependent vibration modes exhibited obvious discrepancies under the highly ergodic condition, while the shift was relatively small around relaxor/ferroelectric crossover. Additionally, polar entities also exhibited discrepant morphology (e.g., composition-regulated one exhibited striped domains, and temperature-regulated one possessed fuzzy signals with partial nanosized domains under the critical condition) and kinetic behaviors (e.g., under highly ergodic condition, temperature-regulated polar entities rebounded slowly at the initial unloading stage). In a word, relatively small structural discrepancies leaded to similar strain performance under the critical condition, while the increasing ergodicity accompanied by increasing structural discrepancies, which finally induced different strain performance under the high ergodic condition. This insight for designing the BNT-based materials with giant electro-strain and low hysteresis was useful to accelerate the industrialization of eco-friendly actuators.