Composition Design And Electrical Properties Of Sodium Bismuth Titanate Based Ferroelectric Ceramics

Bi_0.5Na_0.5TiO₃（BNT）is considered to be one of the most promising lead-free materials due to its high residual polarization strength,high electrostriction and simple preparation process.However,its depolarization temperature is relatively low,resulting in poor temperature stability,which limits its practical application.How to improve its depolarization temperature is currently the research focus of this system.The depolarization temperature can be effectively increased by doping,compounding,quenching and other means,but often accompanied by the deterioration of its ferroelectric properties.Therefore,how to obtain BNT-based ceramic materials with high depolarization temperature and high ferroelectric properties is a key scientific problem to be solved at present.Based on the above background,the depolarization temperature and ferroelectric properties of BNT ceramics can be effectively controlled by doping low valence elements at B site,adding Bi Ga O₃ and doping Zn O.The main research contents and results are as follows:Firstly,effect of Mn/Fe/Co doping on the structure and properties of BNT ceramics.The effects of Mn/Fe/Co doping on the structure,dielectric properties,and ferroelectric properties of BNT ceramics were studied.The results show that Mn/Fe/Co doping is beneficial to the formation of the rhombohedral phase structure.The average grain size increases first and then decreases after Mn/Fe/Co doping.In general,the greater the residual polarization intensity,the better the ferroelectric performance,the remnant polarization P_r of the ceramics doped with Mn/Fe/Co is significantly improved,and the highest P_ris obtained at 0.005 Co（P_r=42.30μC/cm²）.The improvement in ferroelectric properties can be attributed to a reduction in dielectric loss.However,the depolarization temperature T_d decreases after Mn/Fe/Co doping,and it continues decreases with increasing of doping content.Secondly,the effect of BiGaO₃ content on the structure and properties of0.94Bi_0.5Na_0.5(Ti_0.995Mn_0.005)O₃ ceramics was studied.The rhombohedral distortion increased with increasing Bi Ga O₃ from 0%to 2%.When Bi Ga O₃ is increased to x=1.0%,the sample shows excellent ferroelectric properties with a high P_r value（>40μC/cm²）.Furthermore,the effect of Bi Ga O₃ on the depolarization behavior was systematically studied.The depolarization temperature T_d increased from 168℃（x=0%）to 184℃（x=1.0%）,which can be attributed to the inhibition of thermally induced ferroelectric relaxation phase transition by adding Bi Ga O₃.Finally,the structure and sintering properties of 0.97Bi_0.5Na_0.5TiO₃-0.03Bi Al O₃（BNT-BA）ceramics were studied by adding Zn O.The influence of Zn O content on the sintering temperature,densification,ferroelectric properties and depolarization behavior of ceramics was systematically studied.The optimal sintering temperature for increasing Zn O content was reduced from 1140℃to 1000℃,and the grain size was continuously increased and the densification was increased.The ferroelectric properties were optimized by adding Zn O,and the highest P_r（39.84μC/cm²）was obtained at x=2%.The T_d increased from 156℃（x=0%）to 188℃（x=2%）,which may be attributed to the change of Bi³⁺and Na⁺value.After doping Zn O,the ceramics can be sintered at low temperature,which resulted in the increase of Bi³⁺and Na⁺content,and further lead to the increase of T_d.