Large strain response in lanthanide-doped potassium sodium niobate-based piezoceramics

Developing polymorphic phase coexistence near room temperature in potassium sodium niobate-based piezoceramics is a widespread way to improve strain performance. Herein, 0.97(K_0.48Na_0.52)_1-3xLa_xNbO₃-0.03SrTiO₃ piezoceramics were studied by analyzing their grain images, crystal structures, dielectric properties, Raman spectra, ferroelectric properties, strain responses, and piezoelectric properties. A high strain of 0.43% was achieved at x = 0.0050 presenting a diffuse phase transition state, due to various intrinsic factors, including large electrostriction, small piezoelectric effects, and extrinsic microdomain wall reorientation. The large electrostriction was the chief contribution to the strain due to the considerable electrostrictive coefficient (Q₃₃) of 0.039 m⁴/C². Furthermore, the considerable Q₃₃ was due to B-site shifting by distorting the slightly compressed NbO₆ octahedron arising from La³⁺ doping. The compressed of the NbO₆ octahedra was proven by XRD results and generated distortion according to the obtained Raman spectra.