Study On The Composition Design And Electrical Properties Of Sodium Niobium-based Lead-free Ceramics

NaNbO₃（NN）,as a typical lead-free antiferroelectric（AFE）ceramics,have abundant temperature-induced phase transition process.By adjusting the phase structure through composition design,rich electromechanical properties can be obtained.Previous studies mainly focused on the evolution of its phase structure and its strain characteristics,while there were few studies on the application of energy storage.In this paper,with NN as the matrix,the phase structure evolution of NN is controlled by composition design,so as to obtain good ferroelectric and piezoelectric properties.At the same time,the internal mechanism of the effect of the phase structure on the energy storage performance and piezoelectric performance was deeply discussed by many testing methods.The main contents are as follows:（1）The complex substitution of La³⁺and Ti⁴⁺in NN was found to not only effectively stabilize high-temperature AFE R phase,but also induce obvious dielectric relaxor behavior.As a result,obviously enhanced energy-storage properties can be obtained in the composition range of x=0.16～0.20.In combination with the improvement of E_Bvalues of relaxor antiferroelectric NLNT_0.18 as a result of reduced grain size,enhanced resistivity and declined dielectric loss after doping sintering aids,energy-storage properties were further improved.The analysis of HR-TEM and in-situ Raman spectra demonstrates the existence and rapid field-polarization response of APNRs,as well as the resulting high E_AF value up to 30 k V/mm,providing a good understanding of the achievement of excellent energy-storage properties in this work.（2）A new NN-LNT-NS ternary system was prepared by using 0.85NN-0.15LNT as matrix and replacing NN with appropriate amount of Na SbO₃（NS）.the average polarizability of B-site ions reduces by addition of Sb ion,thus stabilizing the AFE phase in NN.At the same time,the addition of Sb ion also reduces the polarization hysteresis of ceramics,which greatly improves the energy storage efficiency（η）of ceramics.The energy storage performance of NN-0.15LNT-0.03NS was further improved by doping sintering aids.Finally,the excellent energy storage performance of W_rec～6.05 J/cm³ andη～80.4%was obtained.And measured the P-E loops in the different temperature and frequency,respectively.The results show that the ceramic has good stability of temperature and frequency,which provides a good foundation for the practical application.（3）LiNbO₃（LN）and NN binary solid solution（1-x）NN-x LN ceramics were prepared by solid-state reaction method.The results show that the addition of LN stabilizes the ferroelectric phase in NN and modulates the low temperature ferroelectric N phase to room temperature.With the addition of LN,the room-temperature phase structure changed from orthorhombic anti-ferroelectric P phase to orthorhombic（O）ferroelectric Q phase and then to rhombohedral（R）ferroelectric N phase.And the excellent electrical properties are obtained at R-O phase boundaries at x=0.12.At the same time,the existence of high temperature T phase was verified by Raman spectra,and the phase diagram of NN-LN binary system was draw,it provides a structural basis for further study.