Bo Shen

Dielectric nonlinear characteristics of Ba(Zr0.35Ti0.65)O3 thin films grown by a sol-gel process

Ba(Zr0.35Ti0.65)O3 (BZT) thin films were deposited via a sol-gel process on Pt-coated silicon substrates. The BZT films were in the perovskite phase and had polycrystalline structure. Temperature-dependent dielectric measurements revealed that the thin films have relaxor behavior and diffuse phase transition characteristics. The tunability K of the dielectric constant (at 600 kV/cm) is about 40% in the temperature range of 179–293 K. The improved temperature stability from this BZT thin film is beneficial to applications requiring a wide range of operating temperatures, thereby eliminating the need for environmental controls. Although the K value is not extraordinarily large compared to (Ba,Sr)TiO3, the low dielectric constant of BZT is attractive for microwave frequency applications. This provides an additional possibility in balancing K and dielectric constant through materials engineering for optimum device performance.

Ultrahigh Piezoelectric Properties in Textured (K,Na)NbO3‐Based Lead‐Free Ceramics

High-performance lead-free piezoelectric materials are in great demand for next-generation electronic devices to meet the requirement of environmentally sustainable society. Here, ultrahigh piezoelectric properties with piezoelectric coefficients (d33 ≈700 pC N-1 , d33 * ≈980 pm V-1 ) and planar electromechanical coupling factor (kp ≈76%) are achieved in highly textured (K,Na)NbO3 (KNN)-based ceramics. The excellent piezoelectric properties can be explained by the strong anisotropic feature, optimized engineered domain configuration in the textured ceramics, and facilitated polarization rotation induced by the intermediate phase. In addition, the nanodomain structures with decreased domain wall energy and increased domain wall mobility also contribute to the ultrahigh piezoelectric properties. This work not only demonstrates the tremendous potential of KNN-based ceramics to replace lead-based piezoelectrics but also provides a good strategy to design high-performance piezoelectrics by controlling appropriate phase and crystallographic orientation.

Type–I pseudo–first–order phase transition induced electrocaloric effect in lead–free Bi0.5Na0.5TiO3–0.06BaTiO3 ceramics

In this study, the electrocaloric effect (ECE) of Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT–0.06BT) ceramic has been directly measured using a home-made adiabatic calorimeter. The maximum adiabatic temperature change (ΔT) approaches 0.86u2009K under an electric field of 5u2009kV/mm at 110u2009°C, which provides experimental evidence for optimizing the ECE near the type–I pseudo–first–order phase transition (PFOPT). Most importantly, a considerable ΔT value can be maintained over a wide temperature range well above the temperature of the PFOPT under a high electric field. In addition, ΔT is closely related to the structural transition and electric field strength. This work provides a guideline to investigate the high ECE in BNT–based ferroelectric ceramics for applications in cooling technologies.

Giant electrostrain accompanying structural evolution in lead-free NBT-based piezoceramics

High-performance (Na0.5Bi0.5)TiO3 (NBT) lead-free incipient ceramics are promising piezoactuator materials, but high driving fields to deliver the large strain limits their practical applications. Herein, we report a giant piezoelectric strain (d33*) of 810 pm V−1 at a low driving field of 4 kV mm−1 in a novel ternary (0.94 − x)(Na0.5Bi0.5)TiO3–0.06Ba(Zr0.05Ti0.95)O3−x(Sr0.8Bi0.1□0.1)TiO2.95 solid solution with x = 0.05 (SBT5). The field of SBT5 critical composition is notably reduced compared with other NBT-based ceramics, while its strain properties are maintained at a high level along with an excellent thermal stability. The dopant induces a randomly distributed local polarization field, which breaks the symmetry of Landau potential curves, boosts the ferroelectric instability and favors a more disordered relaxor structure. The giant strain in the critical composition SBT5 is due to a field-induced reversible relaxor-ferroelectric phase transformation, while the reduced driving field results from two synergistic effects: remanent quasi-ferroelectric order as the seed for the growth of polar domains helps the system skip the nucleation process; the local defects further facilitate the growth of ferroelectric domains. The composition, temperature and electric-field dependence of structural evolutions were systematically elucidated from the micro- and macroscopic view. This study opens up a feasible and effective way for achieving giant electrostrain in lead-free actuator materials.