Study On The Influence Of Sodium Strontium Niobate On The Dielectric And Energy Storage Properties Of Bismuth Sodium Titanate-based Lead-free Ceramics

Bi0.5Na0.5TiO3(BNT)-based relaxor ferroelectric ceramics are a wide-temperature capacitor dielectric material that is expected to be used in high-temperature fields due to its high dielectric constant and Curie temperature.Aiming at the common problems in the doping modification of BNT with compounds with perovskite structure in the current research.The widening of the temperature zone with stable dielectric constant is always accompanied by a decrease in dielectric constant.At the same time,its loss,energy storage density and temperature stability cannot meet actual use requirements.This paper proposes a new idea of introducing a small amount of tungsten bronze medium with a different structure into the perovskite-structured BNT-based ceramic as an additive to modify the dielectric and energy storage performance,by disrupting the ferroelectric long-range order and enhancing dielectric relaxation,thereby improving the dielectric temperature stability and energy storage performance of ceramics.The main research work of this paper is as follows:(1)(1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xSr0.8Na0.4Nb2O6(BNT-BT-xSNN)ceramics were prepared by traditional solid-phase method.The influence of SNN with different additives on phase structure,microscopic morphology,dielectric properties and energy storage properties of BNT-BT-xSNN ceramics was studied,and reveal related physical mechanisms.It found that the addition of SNN resulted in a decrease of anisotropy in the unit cell,and the pseudo-cubic phase was dominant.Dielectric temperature spectroscopy shows that the uneven composition caused by SNN weakens the mutual coupling between polar nanoregions(PNRs),expands the coexistence temperature zone of trigonal and tetragonal nano-polar nanoregions,and significantly improves the temperature stability of dielectric and energy storage properties.Among them,BNT-BT-0.02SNN ceramic has a high dielectric constant and excellent temperature stability in a high temperature and wide temperature range.Its dielectric constant is 3304 at 150℃ and 1 kHz.The dielectric constant ε’ satisfies the condition of Δε’|ε’150℃≤15%in the stable temperature range of 54-418℃,and the dielectric loss tanδ satisfies the condition of tanδ≤0.02 in the temperature range of 102-420℃.At the same time,BNT-BT-0.02SNN ceramics have a Wrec change rate of 6.25%and a η change rate of 9.64%in the temperature range from room temperature to 180℃,showing good energy storage temperature stability.(2)(1-x)[0.98(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.02Sr0.8Na0.4Nb2O6]-xNaNbO3(BNT-BT-SNN-xNN)ceramics were prepared by traditional solid-phase method.Further disrupts the long-range order of ferroelectrics by introducing antiferroelectric NN.And studies its influence on the density,breakdown field strength and energy storage properties of BNT-based ceramics and related mechanisms.It found that the addition of NN helps to increase the density of ceramics and refine the grains,thereby increasing the breakdown field strength.The unique complex phase transition of NN turns the ceramic into an ergodic relaxation ferroelectric,which improves its energy storage properties,and obtains a larger energy storage density Wrec of 1.67 J/cm3 at 140 kV/cm.Furthermore,the energy storage density and efficiency have good temperature stability.From room temperature to 160℃,the rate of change of Wrec and η is less than 8.70%and 1.99%,respectively.The charge and discharge results show that the BNT-BT-SNN-xNN ceramic has a faster discharge rate.t0.9 is 0.10 μs.And the maximum CD and PD are 899.58 A/cm2 and 62.97 MW/cm3 under the critical electric field of 140 kV/cm.From room temperature to 100℃,the variance of CD and PD are both 4.15%,which indicates excellent charge and discharge properties.