Research On Preparation Process Optimization And Energy Storage Enhancement Mechanism Of Silver Niobate Ceramics With High Energy Storage Density

As one of the most critical components in pulse power equipment,solid-state dielectric capacitors have attracted increasing attention for high power density and ultra-fast charge and discharge rate.However,their energy storage density is usually small,and they are easily restricted by energy storage efficiency,thermal stability and fatigue characteristics,resulting in the failure of the capacitor in service.Lead-based antiferroelectric materials are representative materials in the field of solid dielectric capacitors,but they will cause serious damage on human health and natural environment in the process of preparation,application and disposal.Therefore,It is very important to design and develop lead-free antiferroelectric materials with high energy storage density,high energy storage efficiency and excellent performance stability.AgNbO₃-based antiferroelectric ceramics are a type of potential lead-free energy storage ceramics due to their relatively simple phase structure and high saturation polarization under electric field.In this paper,so as to obtain AgNbO₃-based lead-free antiferroelectric ceramics with high energy storage density and efficiency,the phase structure,microstructure and electrical properties of AgNbO₃-based lead-free antiferroelectric ceramics doped with Ca(Hf_0.2Ti_0.8)O₃,Ba Cu（B₂O₅）and(Sr_0.7Bi_0.2)Hf O₃ are studied by solid-phase sintering method based on the principle of"band gap E_g adjustment and liquid phase sintering".Firstly,0.2 wt.%Mn-doped（1-x）AgNbO₃-x Ca(Hf_0.2Ti_0.8)O₃（AN-CHTx,x=0.00～0.08）ceramics were designed based on the principle of“band gap E_g adjustment”The ceramic samples were prepared by solid state reaction method in flowing oxygen atmosphere.With the increase of Ca(Hf_0.2Ti_0.8)O₃ doping,the band gap E_g is widened,the stability of antiferroelectricity is enhanced,the resistivity is increased,and the concentration of vacancy oxygen is decreased.All of these effectively improve the dielectric breakdown field E_b and antiferroelectric-ferroelectric phase transition field E_Fof AN-CHTx ceramics.Consequently,an ultrahigh recoverable energy density W_rec of 5.4J/cm³ together with a relatively high energy conversion efficiencyηof 66%is achieved under an electric field of 300 k V/cm in AN-CHT0.06 ceramic.Meanwhile,AN-CHT0.06ceramic also exhibits a good thermal stability with W_rec（4.5 J/cm³）andη（69%）at a wide temperature range（25～120℃）under external electric field of 280 k V/cm.It indicates that modulating the band structure and oxygen vacancy of AgNbO₃-based ceramics may lead to the discovery of new antiferroelectric materials with pronounced energy storage properties.Additionally,the preparation of AgNbO₃ ceramics is relatively complicated which need to be held for 6 h around 1090℃in oxygen atmosphere.Therefore,it is important to simplify the preparation process of AgNbO₃ ceramics.High density ceramics can be prepared by adding suitable additives in the process of ceramic sintering.Simultaneously,the addition of sintering aid can reduce the sintering temperature and soak time efficiently.In this paper,we chose Ba Cu（B₂O₅）as sintering aid and designed AN-x Ba Cu（B₂O₅）（AN-x BCB,x=0.00～0.02）ceramic system so as to explore the effect of different concentrations of Ba Cu（B₂O₅）on electric performance of AgNbO₃ ceramic.The results show that the sintering temperature and dielectric loss of AN-x BCB ceramics decrease with the increase of Ba Cu（B₂O₅）doping.When x=0.01,the ceramic samples with high density are obtained at 1000℃for 2 h,and the dielectric loss decreases to the minimum value which is0.00989 at room temperature.Meanwhile,the maximum values of W_rec andηare 1.65J/cm³ and 30.4%as the doping of Ba Cu（B₂O₅）reach to 1 mol%,respectively.The preparation process of AgNbO₃ ceramics is simplified.Finally,a strategy of band gap adjustment combined liquid-phase sintering is considered.In this paper,we designed（1-x）AgNbO₃-x(Sr_0.7Bi_0.2)Hf O₃（AN-100x SBH,x=0.00～0.06）ceramics with the addition of 1 mol%Ba Cu（B₂O₅）.AN-100x SBH ceramics with high density can be formed at 1000～1030℃holding 2 h.It indicates that the stability of antiferroelectricity and dielectric breakdown field E_b are significantly enhanced with increasing(Sr_0.7Bi_0.2)Hf O₃ modification as well as the band gap E_g is widened.High W_recandηvalues of 6.1 J/cm³ and 73%,respectively,under an applied field of 330 k V/cm are achieved in the AN-5.5SBH ceramic.Meanwhile,the AN-5.5SBH ceramic shows excellent thermal stability over a wide temperature range of 25～120℃under an externally applied field of 290 k V/cm,in which the fluctuations of W_rec andηare 3.8%and 1.5%,respectively.