Strain, temperature, and electric-field effects on the phase transition and piezoelectric responses of K_0.5Na_0.5NbO₃ thin films

A KNbO₃-based solid solution system is environmentally friendly with good electromechanical performance. This work established the misfit strain-strain and temperature-strain phase diagrams for K_0.5Na_0.5NbO₃ thin films and calculated the polarization switching, phase transition, and piezoelectric responses of K_0.5Na_0.5NbO₃ thin films under various strains, temperatures, and electric fields. The results show that the piezoelectric coefficient d₃₃ can be enhanced near the phase boundaries. For the ferroelectric phase with a nonzero out-of-plane polarization component, an optimal electric field is identified for maximizing d₃₃, which is desired in applications such as thin-film piezoelectric micro-electromechanical systems, transducers for ultrasound medical imaging, and energy harvesting. The present results are expected to provide guidance for the future experimental study of K_xNa_1-xNbO₃ thin films and the optimization of ferroelectric thin film-based devices.