High-performance KNN-based ceramics: inter-granular coupling effect
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In order to achieve the long-term objective of high-performance KNN-based ceramics, BiMnO3-modified lead-free KNN-based ceramics were fabricated by conventional solid-state method in this work. The R–O–T multi-phases coexistence and the absence of Sb doping lead to a large piezoelectricity (d33 = 440 pC/N), a high Curie temperature (TC = 310 °C), and a good in situ temperature stability (d33 is more than 300 pC/N below 100 °C). Based on the high performance, the effects of phase structure and microstructure on electrical properties were carried out by different sintering methods. All the results indicate that phase structure plays a major role on the excellent performance. And the sample with bimodal grain size distribution has a better electrical response than the one with uniform coarse grain size distribution, which can be elucidated by the inter-granular coupling effect. For the sample with bimodal grain size distribution, the large grains endure weaker inter-granular constraints from the surrounding refined grains, while much stronger constraints exist in the sample with uniformly coarse grains.
The authors sincerely appreciate the support of the National Science Foundation of China (NSFC No. 51722208), the Key Technologies Research and Development Program of Sichuan Province (2018JY0007).