Rare earth dopping,especially samarium(Sm)dopping is considered as an effective way to obtain high piezoelectricity by increasing local structure heterogeneity in Pb-containing ABO3 perovskite ceramics.Defects play an significant role in determining piezoelectric properties in aliovalent ion doping systems.In order to obtain an insight into the effect of defects,especially B-site vacancies on piezoelectricity,Sm-doped PZT(54/46)ceramics compensated by B-site vacancies are fabricated by conventional solid state reaction method.The influence of defects on piezoelectric properties is studied by positron annihilation lifetime spectroscopy(PALS),coincidence Doppler broadening spectroscopy(CDBS),and conventional methods such as X-ray diffraction(XRD),scanning electron microscope(SEM),electrical performance testing on dielectricity,ferroelectricity and pizoelectricity.The XRD results show that all ceramics crystallize in a pure perovskite phase,Sm3+doping causes a transformation from the rhombohedral to tetragonal phase and the morphotropic phase boundary(MPB)lies near Sm3+doping content x=0.01-0.02.Electrical performance testing results indicate that with the increase of x,all of the dielectricity,ferroelectricity and pizoelectricity first increase and then decrease,the sample with x=0.01 and 0.02 exhibit similar excellent dielectricity and ferroelectricity,while their pizoelectricity differs greatly,the optimal piezoelectric coefficient d33=572 pC/N(nearly double that of undoped sample)is obtained in the sample with x=0.01.The PALS results show that Sm doping leads the defect types to change from the coexistence of A-site and B-site vacancies for x≤0.01 to mainly A-site related defects for x ≥ 0.02.The CDBS results further verify that the concentration of B-site vacancies is highest for x=0.01 and lowest for x=0.02.It is inferred that the high pizoelectricity for x=0.01 is related to its high concentration of B-site vacancies,which can dilute the number of A-site vacancies and oxygen vacancies,reducing the chance of forming defect dipoles between an A-site vacancy and an oxygen vacancy,facilitating domain wall motion,and enhancing piezoelectricity.This study indicates that B-site vacancies can enhance piezoelectricity to some extent,which will provide some guidance for defect engineering.
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