High and Frequency‐Insensitive Converse Piezoelectric Coefficient Obtained in AgSbO 3 ‐Modified ( Li , K , Na )( Nb , Ta ) O 3 Lead‐Free Piezoceramics

AgSbO 3 was doped into KNN ‐based lead‐free piezoceramics with an optimized composition of Li 0.02 ( Na 0.53 K 0.48 ) 0.98 Nb 0.8 Ta 0.2 O 3 (abbreviated as LKNNT ) to further enhance its piezoelectric property. The doping of AgSbO 3 was found to be effective in reducing the grain sizes, resulting in more uniform microstructure in AgSbO 3 ‐doped LKNNT ceramics. AgSbO 3 lowers tetragonal‐orthorhombic phase transition point ( T T‐O ), but with a more gentle rate as compared with other dopants. A large converse piezoelectric coefficient d 33 * up to 598 pm/V under a relatively low electric field of 1 kV/mm was obtained in the LKNNT ‐5 mol% AgSbO 3 composition, whose tetragonal‐orthorhombic phase transition point ( T T‐O ) was controlled near room temperature, but its Curie temperature was kept at 235°C. The d 33 * obtained in the present material is a very high value for nontextured KNN ‐based ceramics, which is attributed to the polymorphism phase transition effect and “soft” behavior caused by the addition of AgSbO 3 .