Large Electrostrain in K(Nb1−xMnx)O3 Lead‐Free Piezoelectric Ceramics

K(Nb1−xMnx)O3 (KN1−xMx) ceramics with 0.005 ≤ x ≤ 0.015 were sintered at 1020°C through a normal sintering process without the formation of a liquid phase. They exhibited double polarization versus electric field (P–E) hysteresis and sprout-shaped strain versus electric field (S–E) curves owing to the presence of a defect dipole (PD), which was formed between the acceptor Mn3+ ion and the oxygen vacancy. Moreover, the aging process was not required to develop the PD. The KN1−xMx ceramics exhibited a large strain of ~0.2% at 6.0 kV/mm. For the KN0.985M0.015 ceramic, this large strain was maintained after 104 cycles of an electric field of 6.0 kV/mm. This ceramic also maintained a double hysteresis curve at 200°C. Therefore, the KN0.985M0.015 ceramic has a large electric field-induced strain, along with good thermal and fatigue properties for multilayer piezoelectric actuators.