Study On Structure And Properties Of Positionally Doped Ba(Ti_0.92Sn_0.08)O₃ Ceramics

In recent years,Ba(Ti1-xSnx)O3(BTSx)-based lead-free ceramics have become one of the most potential lead-free systems to replace lead-based ceramics due to their excellent piezoelectric,dielectric and ferroelectric properties.A wide range of applications are found in actuators,ferroelectric random access memories,multilayer piezoelectric devices and capacitors.In addition,BTSx-based ceramics have been reported to have competitive piezoelectricity compared to PZT-based ceramics by ion doping.Therefore,Ba(Ti0.92Sn0.08)O3(BTS0.08)was designed as the basic component.The A-site Ca single doping,A-site Li-Al and Li-Nb were prepared by the traditional electronic ceramic solid phase synthesis process.BTS0.08 lead-free piezoelectric ceramics are co-doped to improve the electrical properties of ceramics.Through XRD,SEM,ROMAN and other test analysis techniques,The effects of A-site ion doping on the morphology,phase structure,dielectric properties,piezoelectric properties,ferroelectric properties,electrostrictive effects and dielectric tunability of BTS0.08 lead-free piezoelectric ceramics were investigated systematically.(1)A-site Ca-doped Ba1-xCax(Ti0.92Sn0.08)O3-0.5%Mn02(BCxTS0.08-M)ceramic:A system having a composition(x=0.01,0.03,0.05,0.07,0.09)was prepared by a conventional solid state reaction method.It is confirmed by X-ray diffraction,Raman diffraction and ferroelectric phase diagram that the ceramic transitions from the orthogonal phase(x<0.03)to the orthogonal phase and the tetragonal phase(x=0.05)at room temperature and then transforms into a tetragonal phase(x?0.07).The moderate doping of Ca gradually reduces the relaxation of BCxTS0.08-M ceramics,and almost no change in the depolarnzation temperature of the sample indicates good temperature stability of the ceramic.The piezoelectric coefficient d33,the plane electromechanical coupling coefficient kp,the unipolar strain Smax,the converse piezoelectric coefficient d 33*,the bias field piezoelectric constant d33max of BCxTS0.08-M ceramics all achieve the best value at x=0.05:d33-700pC/N,kp= 0.497,SmaX = 0.054%@ 5kV/cm,d33*=1084pm/V @ 5kV/cm and d33max=1565 pm/V.These results indicate that the low energy barrier is beneficial for improving the piezoelectric performance for the domain polarization rotation and extension in the orthogonal-tetragonal(O-T)two-phase coexistence region.(2)A-position Li-Al co-doped Ba1-2xLixAlx(Ti0.92Sn0.08)O3-0.5%MnO2(BLxAxTS0.08-M)ceramic:A system having a composition(x=0,0.5%,1.0%,1.5%,2.0%,2.5%)was prepared by a conventional solid state reaction method.Appropriate amount of Li-Al doping increases the relative density of BLxAxTS0.08-M ceramics,but the average grain size gradually decreases.It is confirmed by X-ray diffraction and ferroelectric phase diagram that the composition at room temperature(x=0-2.5%)is orthogonal phase.In addition,the optimum bias field piezoelectric coefficient cm3axand the appreciable dielectric adjustable efficiency ?r can also be obtained by adjusting the small signal voltage.Piezoelectric coefficient d33,plane electromechanical coupling coefficient kp,remanent polarization Pr,unipolar strain Smax,the converse piezoelectric coefficient d33*,bias field piezoelectric coefficient d33max,dielectric tunability efficiency ?r and the quality factor FOM of BLxAxTS0.08-M ceramic achieve the best value at x=0.05:d33=620pC/N,kp = 0.457,Smax=0.068%@5kV/cm,Pr = 12.63?C/cm2,d33*=1360pm/V @ 5kV/cm,d33ax=1003 pm/V,?r= 96.91%,FOM = 19.38.In addition,a good electrostrictive effect was observed in the composition x = 0.5%,and the large electrostrictive coefficient Q33=0.034m4C-2 shows excellent temperature stability in the temperature range of 25 ? to 90 ?.(3)A-position Li-Nb co-doped Ba1-2xLixNbx(Ti0.92Sn0.08)O3-0.5%MnO2(BLxNxTS0.08-M)ceramic:A system having a composition(x=0,0.25%,0.50%,0.75%,1.20%)was prepared by a conventional solid state reaction method.Appropriate amount of Li-Nb doping reduced the average grain size of BLxNxTS0.08-M ceramics,but the relative density and relaxation increased slightly.The composition at room temperature was confirmed by X-ray diffraction and ferroelectric phase diagram(x=0.1.20%)is the quadrature phase.The piezoelectric coefficient d33,the plane electromechanical coupling coefficient kp,the remanent polarization Pr,the unipolar strain Smax,the converse piezoelectric coefficient d 33*,and the bias field piezoelectric coefficient d33max of BLxNxTS0.08-M ceramic achieve the best value at x=0.5%:d33:805pC/N,kp = 0.519,Pr=12.60?C/cm2,Smax = 0.13%@ 30kV/cm,d33*= 433 pm/V @ 30kV/cm,d33max=1620 pm/V.Further,a good electrostrictive effect was observed also in the composition x=0.50%,and the large electrostrictive coefficient Q33=0.035m4C-2 shows excellent temperature stability in the temperature range of 25 ? to 90 ?.