High unipolar strain in samarium-doped potassium–sodium niobate lead-free ceramics
Abstract
In this work, a high unipolar strain has been developed in the 0.9675(K0.48Na0.52)(Nb0.915Sb0.035Ta0.05)O3–0.0325(Bi1−xSmx)0.5(Na0.82K0.18)0.5ZrO3 (KNNST-B1−xSxNKZ) ceramics by introducing Sm, and the composition dependence of their phase structures and electrical properties is also discussed. The addition of Sm3+ can change the phase structure of the ceramics by simultaneously shifting TR–O and TO–T to a higher temperature, and we obtained a rhombohedral–orthorhombic–tetragonal coexistence phase (R–O–T) with x = 0, a coexistence phase having orthorhombic and tetragonal (O–T) phases with 0.05 ≤ x ≤ 0.60 and an orthorhombic phase with 0.8 ≤ x ≤ 1.0. In addition, the doping with Sm3+ can greatly enhance the unipolar strain of the ceramics without significantly sacrificing its TC, and a high unipolar strain (∼0.28%) was observed in the ceramics with x = 0.20. More importantly, a large Smax/Emax of ∼833 pm V−1 was also observed in the ceramics with x = 0.20 under a low applied electric field of 1.8 kV cm−1. We believe that such a high unipolar strain can benefit the practical applications of actuators.