Phase Boundary Modulation And Energy Storage Properties Of Sodium Niobate Based Lead-free Ceramics

Nowadays there is a growing concern over ceramic dielectric capacitors with the characteristics of fast charge/discharge rate and high-power density as the core components of integrated circuits.Antiferroelectric energy storage materials have been widely used in the field of dielectric capacitors because of their excellent energy storage properties.At present,lead-based antiferroelectric energy storage materials based on lead zirconate（Pb Zr O₃）have been widely studied.However,with the enhancement of people’s awareness of green protection,the potential threat of lead-based materials to human body and the environment has become increasingly prominent.Therefore,the development of novel lead-free antiferroelectric energy storage materials has become a research hotspot today and even in the future.Sodium niobate（NaNbO₃）is considered as a potential lead-free antiferroelectric material due to its advantages of low density,low raw material cost and complex structural phase transition.However,the unstable antiferroelectric P phase of pure NaNbO₃ can be induced into the irreversible ferroelectric Q phase under the applied electric field,which is not conducive to the improvement of energy storage density.Based on the above problems,this paper designed and studied the phase structure of NaNbO₃ through a series of modification strategies,aiming to optimize the energy storage properties of NaNbO₃.Na(Nb_1-xTa_x)O₃ ceramics were successfully prepared through introducing the Ta⁵⁺into NaNbO₃ matrix to reduce the B-site ion polarizability.The XRD and Rietveld refinement results showed that the coexistence of NaNbO₃antiferroelectric phase and NaTaO₃ paraelectric phase can be achieved when x was in the range of 0.45～0.55.Ferroelectric analysis revealed that the paraelectric phase Na Na O₃ can effectively suppress the generation of irreversible ferroelectric Q phase.And a smaller remnant polarization and a larger saturation polarization can be obtained at x=0.5.The energy storage density of Na(Nb_0.5Ta_0.5)O₃ ceramic was up to 2.2 J/cm³ under 300 k V/cm with an efficiency of 79%.In the case of variable temperature and frequency conditions,the energy storage density ranged from 1.0～1.2 J/cm³,and the energy storage efficiency was more than 84.4%,achieving the optimization of the energy storage characteristics of NaNbO₃ ceramics.To further improve the energy storage properties of NaNbO₃,（1-x）NaNbO₃-x CaTiO₃ ceramics were prepared by the A/B site co-doping strategy.A comprehensive analysis by XRD,TEM,Raman spectroscopy and dielectric properties indicated that the introduction of CaTiO₃ leaded to the structural mutation.When x was between 0.12 and 0.18,the phase boundary of multiphase coexistence can be obtained,resulting a significant increase in the polarization.SEM and impedance analysis exhibited that the introduction of CaTiO₃ was beneficial to the improvement of breakdown field strength.With the electric field of 300 k V/cm,the energy storage density of the 0.82NaNbO₃-0.18CaTiO₃ ceramic was enhanced to 2.5 J/cm³with an efficiency of 80%.The energy storage density of the ceramic varied from 1.8～2.0 J/cm³ at 250 k V/cm under variable temperature and frequency,and the energy storage efficiency remained above 77%,exhibiting excellent temperature and frequency stability.In order to further improve the breakdown strength,the interface of0.82NaNbO₃-0.12CaTiO₃ ceramic was regulated by MnO₂.Both SEM and impedance analysis displayed that the introduction of MnO₂ facilitated to the densification of the ceramics,effectively reducing the oxygen vacancy defect concentration and increasing the breakdown strength from 300 k V/cm to 370k V/cm.In addition,when MnO₂ was up to 1.5 mol%,an energy storage density of 4.1 J/cm³ was achieved in ceramics with an energy storage efficiency of 93%.Under the condition of variable temperature and frequency,the energy storage density of the ceramics varied from 2.6～3.1 J/cm³ with efficiency reaching more than 88%.The results demonstrated that 0.82NaNbO₃-0.12CaTiO₃ ceramics modified by MnO₂ have excellent application prospect in the field of dielectric energy storage.To sum up,this paper proposes a multiphase coexistence strategy combined with micro-interface optimization,aiming to improve the energy storage density of NaNbO₃based ceramics,which provides a new idea for the development of novel high-performance energy storage ceramics.