Effect On Structure And Properties Of Nbt-based Lead-free Ceramics With Tiny Elements Doping

As a common energy storage device,dielectric capacitors are widely used in pulse power fields such as medical and military attribute to the advantages of ultra-high power density,fast charge-discharge time and excellent cycle times.As its core component,dielectric materials directly affect its energy storage characteristics.Therefore,these research studies on highenergy storage dielectric materials have gradually become an interesting question.This paper took NBT ceramics as the starting point and introduced different radii of ions into the NBT-SBT binary to achieve A/B substitution.We prepared the(0.65Bi0.5Na0.5-0.35Bi0.2Sr0.7)(Ti1-xNbx)O3(abbreviated as:BNBS-Ti1-xNbx),0.65[Bi0.5(Na1-xMgx)0.5]TiO3-0.35Bi0.2Sr0.7TiO3(abbreviated as:(Na1-xMgx)BT-SBT)and(0.65Bi0.5Na0.5-0.35Bi0.2Sr0.7)(Ti1-xZrx)O3(abbreviated as:BNBSTi1-xZrx)ceramic samples,which combined throughing literature extensively and experiments specifically to determine the parameters including sintering temperature,holding time and others.Finally,the electrical characterization was tested to study the energy storage density under different doping amounts and the frequency and temperature stability of the sample.The main research results of this paper are as follows:1)The BNBS-Ti1-xNbx ceramic system was formed by introducing Nb2Os into NBT-SBT ceramics through the traditional solid-phase sintering method.It was found that there were some extra diffraction peaks excepting the typical perovskite structure.Dielectric tests show that after the introduction of Nb5+,the BNBS-Ti1-xNbx obtained by 1100℃ sintering is in the frequency range of 102-107 Hz,and the εr of the sample decreases and the tanδ increases,meeting the dielectric characteristics of the standard ferroelectric body.The ferroelectric performance tests showed that the electric hysteresis loop of sample BNBS-Ti0.98Nb0.02)is fine,and the loss is low,which energy storage density at 90 kV/cm is Wrec=1.26 J/cm3,η=71.71%.2)The(Na1-xMgx)BT-SBT ceramic system was prepared by introducing tiny MgO elements into the A site in NBT-SBT ceramics.It was found that Mg2+ substituted larger Na+into the matrix of NBT-SBT and formed a solid solution.The minimum grain size is 0.39 μm at the(Na0.975Mg0.025)BT-SBT sample.Dielectric tests show that the dielectric properties of ceramic samples sintered at 1110℃ are superior and the(Na0.98Mg0.02)BT-SBT sample can achieve a greater value of εr is 2171.It can be seen that the introduction of Mg2+can further improve the relaxation characteristics.As the dielectric temperature spectrum indicates,the sample Ts transfers to low temperature and Tm slightly transfers to high temperature after doping,so the material can show relaxation characteristics at low temperature.The ferroelectric performance tests showed that the Pmax value of each sample was effectively increased after doping.The(Na0.975Mg0.025)BT-SBT samples show excellent energy storage characteristics,with Wrec of 1.05 J/cm3,η of 82.63%(at 80 kV/cm).These indicate that MgO doping can adjust the ceramic phase structure effectively and improve the dielectric properties and energy storage properties.3)To further enhance the breakdown field strength,the BNBS-Ti1-xZrx ceramic samples were prepared by introducing trace ZrO2 into the B-site of the NBT-SBT based ceramic system.It was found that the doped ions completely entered the lattice of the original matrix,showing a good perovskite structure.All the samples show uniform grain size and a clear grain boundary.The minimum grain size is obtained in BNBS-Ti0.97Zr0.03 samples,which is beneficial to obtain higher breakdown strength.The dielectric constant εr of BABS-Ti1-xZrx ceramics decreases gradually with the increase in doping content,while the tanδ value does not change obviously.At 1 kHz,the Tm of each component decreases with the increase in doping content,which is related to the fact that Zr4+ enters the lattice of TiO6 octahedron after doping.The oxygen octahedron of TiO6 is more prone to tilt and distortion after doping,which reduces the unique activation energy of ions.The ferroelectric performance tests show that all samples possessed good energy storage characteristics,BNBS-Ti0.97Zr0.03 exhibited excellent energy storage characteristics Wrec=1.47 J/cm3 and η=86.94%(at 100 kV/cm).The relationship between Wrec and η is well balanced.Compared with other NBT-based lead-free ceramics,the results provide a basis for the preparation of pulse power capacitors using NBT based ceramics.According to the above research content,the introduction of Nb5+,Mg2+and Zr4+into the NBT-SBT based ceramic can construct the relaxation ferroelectric phase,increase the polarization difference,and refine the hysteresis loop to improve the energy storage performance of the material.Among them,Nb5+can improve the thermal stability of the sample so as to broaden the temperature range of the ceramic.The doping of Mg2+ can reduce the Tm point of the NBT ceramics,which effectively reduces the Pr of the material.While Zr4+ can improve the dielectric properties of the sample,the wider energy band is also conducive to the improvement of BDS.Thus,the research of this paper provides an effective method for obtaining pulse power capacitors with good energy recovery characteristics and high efficiency.