Improving strain in single crystal by composition-gradients design

Domain switching is one of the essential contributions for strain in ferroelectric materials. In this work, we utilize anisotropic composition gradients (CGs) to induce anisotropic orientation of both defects and spontaneous dipoles, aiming to enhance the contribution of domain switching on strain in KTa_1–xNb_xO₃ single crystal. In this way, a remarkable improvement (over 60%) of strain is obtained in KTa_0.58Nb_0.42O₃ single crystal along the smallest CG direction, achieving a large unipolar strain, i.e. 0.29%, at low driving electric field 10 kV cm^–1. It is attributed to the preferred orientation of both defects and spontaneous dipoles along the largest CG directions, then improving the contribution of domain switching on strain along the smallest CG direction. Particularly, owing to the existence of E_in as recoverable forces caused by both flexoelectric fields and defects pinning effect, KTN show nearly zero remnant strain (s_rem) along with the small CG directions, corresponding to the double P-E loops. Moreover, the V–PFM images confirm that CGs can influence the microdomain structures. Thus, designing special anisotropic CGs materials is expected to be a novel method to improve the strain properties and a potential way to flexibly design next-generation anisotropic piezoelectric materials.