A Study on the Relationship Between Grain Size and Electrical Properties in (K,Na)NbO3‐Based Lead‐Free Piezoelectric Ceramics

Abstract

AbstractThe 0.5 wt% MnO2‐doped 0.95(K0.5Na0.5)(Nb0.965Sb0.035)O3‐0.01CaZrO3‐0.04(Bi0.5K0.5)(Hf0.98Ti0.02)O3 (95KNNS‐1CZ‐4BKHT) lead‐free ceramics with grain size from 0.31 to 3.83 µm are fabricated by hot‐press sintering (HPS), microwave sintering (MS), conventional sintering (CS), two‐step sintering (TSS), and a combination of two of the above‐mentioned methods. Then, the grain size effects on the phase transition, electrical properties, domain structure, and temperature stability of the ceramics are investigated. The phase structure evolves from single rhombohedral (R) phase to coexisted rhombohedral‐tetragonal (R‐T) phases around 1 µm. The electromechanical properties are strongly grain size dependent. The values of piezoelectric coefficient (d33) and planar electromechanical coupling factor (kp) first rise sharply when the grain size is less than 1 µm, and then increase mildly in the grain size range from 2.55 to 3.04 µm and finally almost remain a constant (≈450 pC N−1 and 54%) when the grain size is larger than 3.31 µm. The R‐T phase coexistence and strip‐like nanodomain structure characterized by an easier switching feature contribute to the high piezoelectric and electromechanical properties of coarse‐grained samples. This work not only clarifies the relationship between grain size and electrical properties in KNN‐based ceramics, but also provides a novel strategy for developing high‐performance lead‐free piezoceramics.