Effects Of A-site Ion Radius Adjustment Of NBT-based Lead-free Piezoelectric Ceramics On Structure And Properties

Sodium bismuth titanate-barium titanate(Na_0.5Bi_0.5TiO₃-x%BaTiO₃,abbreviated as NBT-x%BT)is potential lead-free piezoelectric ceramic that might replace lead-based ceramics in some applications,such as actuators,sensors,and transducers.There is a morphotropic phase boundary?MPB?for NBT-x%BT near the x=6?7 where piezoelectric and dielectric properties are enhanced.However,the transition between inphase and antiphase octahedral rotations leads to depolarization in NBT-x%BT ceramics,which hinders the practical applications of NBT-x%BT ceramiacs.Octahedral rotations in ABO₃ perovskite can be modified with changing the atomic sizes on A-or B-site.In this dissertation,Mg²⁺?0.065nm?,Ca²⁺?0.099nm?,and Sr²⁺?0.113nm?elments with different radius were selected as dopant on perovskite A-site of NBT-x%BT ceramics.Through the analysis of the ceramic samples structure,dielectric,ferroelectric and piezoelectric properties,the M:NBT-x%BT?M=Mg,Ca and Sr?was explored the internal relationship between the composition,structure and performance of lead piezoelectric ceramics has been found to have very important theoretical value and practical significance in energy storage through research.Firstly,by preparing NBT and NBT-x%BT?x=0,2,4,6,8,10,12?ceramic samples,the appropriate preparation process of piezoelectric ceramics in this paper is established;the regular crystal grain shape of NBT is clear at room temperature,X-ray diffraction analysis shows a monoclinic phase;and the diffusive phase transition coefficient is 1.62;the hysteresis loop shows the correction The stubborn field is 44 kV/cm,the residual polarization is 32?C/cm²,the reversible energy storage density is 0.108J/cm³,and the energy storage efficiency is 2.14%.The NBT-x%BT have the coexistence structure of trigonal and tetragonal phase near MPB;as the value of the trigonal phase compared to the tetragonal decreases,the piezoelectric constant increases from 55pC/N to the maximum value of x=6 is 103 pC/N;the addition of Ba²⁺makes the samples more relaxed and the coercive field gradually decreases;the trend of energy storage density increases first and then decreases to0.418J/cm³ at x=8,and the energy storage efficiency reaches a maximum of 33%.Through the A-site doping,the effect of different ionic radiu on the structure and properties of binary solid solution was studied.The intersection of Na⁺?0.095nm?and Bi³⁺?0.096nm?with a smaller Mg²⁺?0.065nm?results in a larger ceramic grain size,increased dielectric loss;while Ca²⁺?0.099nm?and Sr²⁺?0.113nm?make the matrix ceramic grain size continue to decrease,indicating that the larger the doped ion radius,the smaller the grain size,the piezoelectric performance is maximized at x=8,NBT-8%?Ba,Mg?T is 97 pC/N;NBT-8%?Ba,Ca?T is 85 pC/N;NBT-8%?Ba,Sr?T is 91 pC/N,which is lower than the NBT-x%BT,which may be related to the formation of The lamellar formation layer is related;but the energy storage has been greatly improved.With the increase of the doping ion radius,the reversible energy storage density is continuously increasing,respectively,0.302J/cm³,0.423J/cm³,0.537J/cm³ at x=12 and the energy storage efficiency also reached the maximum,respectively 43%,59%and 73%.Through the Raman scattering experiment,according to the change of the phonon mode of the octahedron represented by the spectrum from400cm^-1 to 700cm^-1,it was found that with the increase of the doping content,according to the peak The three peaks fitted at x=8 with different doping compositions migrate to the high wavenumber segment,indicating that the forces exerted by ions of different radii on the TiO₆octahedron change the vibrational position of Ti⁴⁺at the center,making the TiO₆ octahedron Tilting occurs,and the transition of doped Mg ²⁺,Ca²⁺,Sr²⁺from x=6 to x=8,the high wave number phonon transition value of the corresponding frequency band is?Mg²⁺=5.14cm^-1,?Ca²⁺=3.75cm^-1,?Sr²⁺=15.18cm^-1;it can be seen that with the increase of the ion radius,the vibration and tilt of the TiO₆ octahedron are exacerbated,so that the piezoelectric performance of the sample is increased at the doping content of x=8.