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

Abstract

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 ABO&lt;sub&gt;3&lt;/sub&gt; perovskite ceramics. Defects play an significant role in determining piezoelectric properties in aliovalent ion doping systems. In order to get insight into the effect of defects, especially B-site vacancies on piezoelectricity, Sm-doped PZT(54/46) ceramics compensated by B-site vacancies were fabricated by conventional solid state reaction methods. The influence of defects on piezoelectric properties was studied by positron annihilation lifetime spectroscopy(PALS), coincidence Doppler broadening spectroscopy(CDBS) and conventional methods such as XRD, SEM, electrical performance testing on dielectricity, ferroelectricity and pizoelectricity. XRD results show that all ceramics crystallize in a pure perovskite phase, Sm&lt;sup&gt;3+&lt;/sup&gt; doping causes a transformation from the rhombohedral to tetragonal phase and the morphotropic phase boundary (MPB) lies near Sm&lt;sup&gt;3+&lt;/sup&gt; 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 enhances and then decreases, sample with x=0.01 and 0.02 exhibits similar excellent dielectricity and ferroelectricity, while their pizoelectricity differs widely, the optimum piezoelectric coefficient d&lt;sub&gt;33&lt;/sub&gt;=572pC/N (nearly double compared with undoped sample) is obtained in sample with x=0.01. PALS results show that Sm doping leads to the variation of defect types from the coexistence of A-site and B-site vacancies for x ≤ 0.01 to mainly A-site related defects for x ≥ 0.02. CDBS results further verify that the concentration of B-site vacancies is highest and lowest for x=0.01 and 0.02, respectively. 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 amount of A-site vacancies and oxygen vacancies, reduce the chance of the formation of defect dipoles between an A-site vacancy and an oxygen vacancy, facilitate domain wall motion and enhance piezoelectricity. This study indicates that B-site vacancies can enhance piezoelectricity to some extent, which will provide some guidance for defect engineering.