Doping, Electrocaloric Effect And Energy Storage Properties Of Sodium Bismuth Titanate Based Ceramics

(Bi_0.5Na_0.5)TiO₃ is a new A-site complex perovskite lead-free piezoelectric materials with superior piezoelectric properties.The anisotropy of electromechanical coupling coefficient is significant different?k_t=50%,k_p=13%?,and can be used as thickness vibration,because it can diminish the useless vibration.The curie temperature is higher?320??,and relative dielectric constant is smaller?240³40??.Its pyroelectric properties are close to BaTiO₃ and PbZrTiO₃,and acoustic performance is superior?N_p=3200 Hz·m?.In addition,its sintering temperature is lower,which is below 1200?,and it is one of the candidate of PbZrTiO₃materials.(Bi_0.5Na_0.5)TiO₃ based materials is prepared by conventional solid state method in this paper.The effect on the structure,ferroelectric,dielectric,electrocaloric effect and energy storage properties of Bi_0.5Na_0.5TiO₃ based material doped with other compounds is investigated.Firstly,large electrocaloric effect is observed in La₂O₃ doped(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃?BNBT6?ceramics,which is synthesized by conventional solid state reaction.The dielectric permittivity and ferroelectric hysteresis loops are measured.The indirect method is used to calculate electrocaloric effect of BNBT6 doped by La₂O₃.The introduction of La₂O₃ can enhance the electrocaloric effect.The largest temperature changes|?T₆₂|=2.61 K and electrocaloric coefficient|?_max|=0.052 Kcm/kV is achieved in the x=0.5wt%ceramic.It is significantly higher than that of(Bi_0.5Na_0.5)TiO₃-based ceramic materials reported.In addition,the depolarization temperature of x=1 wt%is shifted to the room-temperature,which makes the|?T₃₀|=1.954 K and|?_max|=0.039 Kcm/kV is also obtained in the room-temperature.Those properties promise the La₂O₃ doped BNBT6 as a superior cooling materials.Secondly,large energy-storage density is observed in BaZrO₃ modified0.80Bi_0.5Na_0.5TiO₃-0.20Bi_0.5K_0.5TiO₃?BNBK?ceramics.The energy storage property of?1-x?BNBK-xBaZrO₃ has been investigated.According to the Weibull model,BaZrO₃ can enhance the energy storage property of BNBK by improving the breakdown strength.The largest energy-storage density W₁=0.73 J/cm³ and efficiency of energy storage?=0.75 under the E=70 kV/cm are achieved in the 0.96BNBK-0.04BaZrO₃,which is significantly higher than that of(Bi_0.5Na_0.5)TiO₃-based and lead-containing ferroelectric materials reported.Its energy-storage density exhibits the superior thermal stability with temperature range of30-100?.Those properties promise the environmental-friendly?1-x?BNBK-xBaZrO₃ceramics are candidate for applications of energy storage devices.Finally,Certain content of NaNbO₃ substitution isn't change the typical perovskite structure of the?1-x?(0.7Na_0.5Bi_0.5TiO₃-0.3Bi_0.2Sr_0.7TiO₃)-xNaNbO₃??1-x?BNBST-x NaNbO₃?,but the secondary phase will appear with the content of NaNbO₃ increased.The introduction of NaNbO₃ will make the transformation between nano-polar region and macro-polar region difficult,and then enhance the breakdown strength,which will be attributed to improve the energy storage density.For x=0.01,the energy storage density 1.3 J/cm³ can be obtained at 90kV/cm and exhibits superior thermal stability,can undergo 500 recycles chanrge and discharge.Its energy storage density and efficiency is larger than the report before,which suggested it is the superior energy storage density.