Composite Scheme for Deferred Thermal Depolarization of Lead-Free Bi0.5Na0.5TiO3-Based Piezoelectric Ceramics.

The relatively low thermal depolarization temperature (Td) has hindered the development and practical application of lead-free Bi0.5Na0.5TiO3-based systems; therefore, a feasible strategy is urgently needed to defer the depolarization behavior. In this work, a perovskite/metal 0.78 Bi0.5Na0.5TiO3-0.22 Bi0.5K0.5TiO3/xAg (BNT-22BKT/xAg) composite ceramic is designed and successfully prepared. The introduction of metal Ag with a larger thermal expansion coefficient leads to an increased fraction and enhanced lattice distortion of the rhombohedral phase, as well as an enlarged domain size. The thermal stability thus is effectively improved, and the optimal Td value of 166 °C is obtained at x = 0.03, which is about 60 °C higher than that of prototype ceramics. This research provides a perovskite/metal composite scheme to increase the depolarization temperature of BNT-based ceramics and promotes their potential for practical applications.

Outstanding Energy-Storage Density Together with Efficiency of above 90% via Local Structure Design.

Dielectric ceramic capacitors with high recoverable energy density (Wrec) and efficiency (η) are of great significance in advanced electronic devices. However, it remains a challenge to achieve high Wrec and η parameters simultaneously. Herein, based on density functional theory calculations and local structure analysis, the feasibility of developing the aforementioned capacitors is demonstrated by considering Bi0.25Na0.25Ba0.5TiO3 (BNT-50BT) as a matrix material with large local polarization and structural distortion. Remarkable Wrec and η of 16.21 J/cm3 and 90.5% have been achieved in Bi0.25Na0.25Ba0.5Ti0.92Hf0.08O3 via simple chemical modification, which is the highest Wrec value among reported bulk ceramics with η greater than 90%. The examination results of local structures at lattice and atomic scales indicate that the disorderly polarization distribution and small nanoregion (∼3 nm) lead to low hysteresis and high efficiency. In turn, the drastic increase in local polarization activated via the ultrahigh electric field (80 kV/mm) leads to large polarization and superior energy storage density. Therefore, this study emphasizes that chemical design should be established on a clear understanding of the performance-related local structure to enable a targeted regulation of high-performance systems.

Enhancing the Temperature Stability of 0.42PNN-0.21PZ-0.37PT Ceramics through Texture Engineering.

Although the MPB composition 0.42PNN-0.21PZ-0.37PT ceramic has high piezoelectric properties, its temperature stability at room temperature is rather poor due to the low phase-transition temperature. By texture engineering using BaTiO3 (BT) as the template, the temperature stability of this material can be greatly improved. In the temperature range from room temperature up to 140 °C, the high effective piezoelectric strain constant d33* of 0.42PNN-0.21PZ-0.37PT-3BT only changed by 4.9% from 1278 to 1215 pm/V, while the d33* of the nontextured counterpart changed by 46.7% from the room temperature value of 920 pm/V with the maximum deviation to 1350 pm/V at 80 °C. In addition, the textured ceramic has higher piezoelectric properties, lower dielectric loss, and slightly higher coercive field. The room-temperature figure-of-merit d33 × g33 for PNN-PZT-2BT is increased by as much as 42% compared with the nontextured counterpart. Our results demonstrated that texture engineering is an effective way to improve the temperature stability of the MPB composition piezoceramics.