Phase Field Simulation Strain And Electric Field Control Domain Structure And Physical Properties Of K_0.5Na_0.5NbO₃ Thin Films

At present,the problem of energy shortage is becoming more and more serious in the world.The environmentally friendly K_0.5Na_0.5NbO₃ thin film ferroelectric material has been widely used in pulse equipment,medical equipment and other fields due to its high power density,but its energy storage density is relatively low,resulting in further application in the field of energy conversion and storage is limited,so it is of great significance to improve its energy storage performance.This article is based on phase field model,and build the K_0.5Na_0.5NbO₃ film biaxial should figure in disguised forms,and calculate the anisotropic biaxial mismatch strain(=-1.5%?1.5%,=-1.5%?1.5%)influence on film domain structure and macro performance.The results show that:with the transition from compressive strain to tensile strain,the orthogonal phase is transformed into monoclinic phase;large compressive strain growth of outside surface₃ domain,large tensile strain to promote the growth of in-plane domain;under both tensile strain and compression strain,applying an applied electric field causes the in-plane domain to turn into out-of-plane domain;as the biaxial strain changes from compressive strain to tensile strain,the residual polarization intensity and coercive electric field tend to decrease;biaxial mismatch should be disguised the picture₁ and₂ domain of the biaxial strain more sensitive to the residual polarization control,biaxial₃ domain mismatch should be a disguised form the picture of the biaxial strain more sensitive to the coercive electric field control;under biaxial tension strain,the more domains in the film plane,the higher energy storage density and efficiency.The effects of electric field rate on domain structure,hysteresis loop and energy storage performance of K_0.5Na_0.5NbO₃ thin films were analyzed by using phase field simulation.The results show that:different directions of electric fields cause different electric domains to flip in the same direction as the electric field;the higher the electric field rate is,the more obvious the hysteresis effect of the domain flipping is,and the higher the electric field intensity is needed to make the domain in the film reach the final steady state;the changing rate of electric field has no obvious effect on the switching path of electric domain and the state of electric domain after reaching the equilibrium state;with the increase of electric field change rate,the residual polarization strength of the film increases,and the energy storage density and efficiency of the film deteriorate obviously due to the increase of dielectric loss.When the electric field change rate is 0.01 V/(m?step),x axis tensile strain is 1.3%,y axis tensile strain was 1.5%,K_0.5Na_0.5NbO₃ film of the energy storage density and reach maximum energy storage efficiency,107.67 J/cm~3 and 95.92%,respectively.It is of guiding significance for the regulation of ferroelectric thin film domain structure and the construction of high efficiency energy storage devices.