Analysis of defects in <i>B</i>-vacancy compensated Sm-doped PZT(54/46) ceramics and their influences on piezoelectric properties

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 <i>AB</i>O₃ 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 <i>B</i>-site vacancies on piezoelectricity, Sm-doped PZT(54/46) ceramics compensated by <i>B</i>-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 <i>x</i> = 0.01–0.02. Electrical performance testing results indicate that with the increase of <i>x</i>, all of the dielectricity, ferroelectricity and pizoelectricity first increase and then decrease, the sample with <i>x</i> = 0.01 and 0.02 exhibit similar excellent dielectricity and ferroelectricity, while their pizoelectricity differs greatly, the optimal piezoelectric coefficient <i>d</i>₃₃ = 572 pC/N (nearly double that of undoped sample) is obtained in the sample with <i>x</i> = 0.01. The PALS results show that Sm doping leads the defect types to change from the coexistence of <i>A</i>-site and <i>B</i>-site vacancies for <i>x</i> ≤ 0.01 to mainly <i>A</i>-site related defects for <i>x</i> ≥ 0.02. The CDBS results further verify that the concentration of <i>B</i>-site vacancies is highest for <i>x</i> = 0.01 and lowest for <i>x</i> = 0.02. It is inferred that the high pizoelectricity for <i>x</i> = 0.01 is related to its high concentration of <i>B</i>-site vacancies, which can dilute the number of <i>A</i>-site vacancies and oxygen vacancies, reducing the chance of forming defect dipoles between an <i>A</i>-site vacancy and an oxygen vacancy, facilitating domain wall motion, and enhancing piezoelectricity. This study indicates that <i>B</i>-site vacancies can enhance piezoelectricity to some extent, which will provide some guidance for defect engineering.