Chunlin Zhao

Site engineering and polarization characteristics in (Ba1−yCay)(Ti1−xHfx)O3 lead-free ceramics

Here we improved both piezoelectricity and strain of BaTiO3-based ceramics using composition designs and the optimization of poling conditions. In this work, the (Ba1−yCay)(Ti1−xHfx)O3 lead-free ceramics were fabricated by a conventional solid-state reaction method, and we systematically investigated the composition dependence of their phase structures, microstructure, electrical properties, and polarization characteristics. A multiphase coexistence concerning rhombohedral-orthorhombic and orthorhombic-tetragonal (R-O/O-T) was observed in the ceramics with xu2009=u20090.10 and yu2009=u20090.15, and then an enhanced piezoelectricity of d33u2009∼u2009540 pC N−1 and a large strain of ∼0.21% can be attained. More importantly, a larger d33 can be reached when sintered at 1450u2009°C and polarized at their corresponding phase transition temperatures. We believe that this investigation can benefit the development of barium titanate ceramics.

Large strain and temperature-insensitive piezoelectric effect in high-temperature piezoelectric ceramics

Here we have, for the first time, reported a giant unipolar strain of ∼0.45% and a temperature-insensitive piezoelectric effect (d33 ∼ 520 pC N−1) in (1 − y)[xBiScO3–(1 − x)PbTiO3]–yBi(Zn1/2Ti1/2)O3 (BS–PT–BZT) ceramics with a high Curie temperature of TC ∼ 425 °C. The morphotropic phase boundary (MPB) of rhombohedral–tetragonal (R–T) phase coexistence can be driven in samples with x = 0.36 and y = 0.01, which is mainly responsible for the enhancement of electrical properties and temperature stability. PFM test results indicate that the addition of BZT can improve the local piezoelectric response of domains, which may lead to the enhancement of piezoelectricity and strain. In addition, ceramics with BZT exhibit good temperature stability of electrical properties. We believe that these materials can be well applied in the field of high-temperature piezoelectric actuators.

Practical high strain with superior temperature stability in lead-free piezoceramics through domain engineering

An easy-to-use domain strategy by utilizing phase boundary design, chemical modification, and electric-field driving was employed to optimize strain and temperature stability of a polycrystalline ceramic. First, the effects of phase boundary, composition, and electric field on the domain were investigated in detail. Distinct spontaneous polarization rotation appears in various phase transition processes, inducing different evolution of domain structure and piezoresponse at elevated temperatures. Measurements reveal that the domain at the rhombohedral–tetragonal (R–T) phase boundary shows giant piezoresponse and high temperature stability. The structure origin is assigned to the slow degradation of spontaneous polarization, and the highly steady domain contribution stimulates excellent strain stability at the R–T phase boundary. Additionally, doped components significantly influenced domain stability, and boosted electric fields stabilized the piezoresponse of the domain. Second, modulating domain stability and its piezoresponse through tuning the phase boundary and driving field, as well as chemical modification, realized a large and temperature-insensitive strain ( fluctuation less than 3% at 23–80 °C) in (K, Na)NbO3 (KNN)-based ceramics. This value is largely superior to that obtained from current lead-free piezoelectric materials and some soft lead-based counterparts, indicating a tremendous application potential for (K, Na)NbO3 (KNN)-based ceramics. This study affords a significant guidance for designing lead-free piezoelectric materials with high piezoelectricity and temperature stability.