LAUSR

Polarization rotation is considered one of the most important intrinsic origins of high piezoelectricity in perovskite ferroelectrics. Such rotation strongly increases the lateral polarization, thus giving rise to the ultrahigh-shear piezoelectric coefficient. The evolution of polarization vector as a function of shear strain in a lead-free perovskite ferroelectric, ${\mathrm{K}}_{0.5}{\mathrm{Na}}_{0.5}{\mathrm{NbO}}_{3}$ (KNN), is demonstrated using the first-principle calculations. The polarization rotation is found to correlate directly with the shear piezoelectric constant. The larger the rotation angle, the higher the shear piezoelectric constant. The atomic insight reveals the polarization rotation mainly relies on the reorientation of Nb and O atoms along low potential-energy surfaces. We propose the polarization vector is more likely to rotate along the ${[111]}_{\mathrm{PC}}\ensuremath{\rightarrow}{[101]}_{\mathrm{PC}}\ensuremath{\rightarrow}{[001]}_{\mathrm{PC}}$ path instead of direct ${[111]}_{\mathrm{PC}}\ensuremath{\rightarrow}{[001]}_{\mathrm{PC}}$ transition in high-performance lead-free piezoelectric materials with broad thermotropic phase boundaries; thus, the critical role of orthorhombic structure should be emphasized. We hope that this work will inspire future experimental studies for further developing lead-free piezoelectric materials.