Study On Polarization Behavior And Energy Storage Properties Of Nb⁵⁺ Doped NBT-ST Based Films

With the wide application of modern electrical and electronic technology,people pay more and more attention to high energy storage density materials.Dielectric capacitors have attracted much attention because of their high discharge power density and fast charging and discharging speed.There are many kinds of dielectric capacitors,among which thin film capacitors have been widely studied because of their high breakdown field strength.However,the energy storage density and efficiency of thin film capacitor are still low,hardt to satisfy the needs of society.Sodium bismuth titanate strontium titanate（NBT-ST）can control the phase transition of NBT-ST by adjusting the content of St,so that NBT-ST can obtain good ferroelectric properties and breakdown resistance at the same time.In this paper,NBT-ST thin film is selected as the research object,and Nb⁵⁺ions are doped in NBT-ST thin film in different phase regions.By changing the concentration of Nb⁵⁺ions,the ferroelectric properties of thin film capacitor are expected to be improved and the energy storage characteristics are optimized.In addition,the multilayer film is expected to achieve the electric field amplification effect,improve the breakdown field strength and improve the energy storage performance.Nb⁵⁺ions are doped in 0.75NBT-0.25ST films in quasi homomorphic phase region,occupying Ti⁴⁺ion site.Due to the balance of electricity price,Ti⁴⁺ions are forced to transform into Ti³⁺ions,and Nb⁵⁺-Ti³⁺ion pairs are successfully formed in0.75NBT-0.25ST films,realizing the unidirectional conduction characteristics of current density.The dipole moment provided by the ion pair produces local polarization and forms a self built electric field,which improves the polarization behavior.In order to further reduce the leakage,Mn²⁺ion with 1 mol.%concentration is introduced to improve the closure of the hysteresis loop,and the line shape becomes"thin".As the increase of Nb⁵⁺ion concentration,the breakdown field strength decreases after the peak value,and the difference between the saturation polarization and the residual polarization is 10μC/cm²–25μC/cm².The maximum energy storage density is 17.4 J/cm³and the efficiency is 45.8%when the content of Nb⁵⁺is1.5 mol.%.Nb⁵⁺and Mn²⁺ions were doped into T-phase 0.65NBT-0.35ST to study its polarization behavior,leakage performance and energy storage characteristics.In this system,Nb⁵⁺-Ti³⁺ion pairs were successfully constructed,and the unidirectional conduction characteristics of current density were realized.In this system,the difference between the saturation polarization and the residual polarization is 10μC/cm²–25μC/cm².The maximum energy storage density is 23 J/cm³ when the content of Nb ⁵⁺is 1 mol.%,and the energy storage efficiency is 45.8%.The NBT-ST films with 0.5 mol.%,1 mol.%,quasi homomorphic and T-phase NBT-ST were prepared.The growth order has no effect on the ferroelectric and energy storage properties of the films,but the high concentration of Nb⁵⁺ions will affect the breakdown field strength and reduce the energy storage density of the films.In addition,the breakdown field strength of the multilayer structure is larger than that of the sandwich structure,but the difference between the saturation polarization and the residual polarization is smaller than that of the sandwich structure.The results show that when the concentration of Nb⁵⁺is 1 mol%,the multilayers with quasi homomorphic structure first and then T-phase have the best polarization behavior and energy storage characteristics.The energy storage density is 48.38 J/cm³,and the energy storage efficiency is 66.313%.