Dielectric and piezoelectric properties of lanthanum-modified 0.55Pb(Sc1/2Ta1/2)O3–0.45PbTiO3 ceramics

The effects of lanthanum addition and annealing (900°C, 8 h) on the Curie temperature, dielectric and piezoelectric properties of lanthanum-modified Pb(1−x)Lax(Sc12Ta12)0.55Ti0.45O3 ceramics (La-doped PSTT) (x=0.005, 0.01, 0.02, 0.03) were investigated. It was found that annealing and the addition of lanthanum can significantly modify all these properties. For the compositions where x=0.005 and x=0.01, many ‘abnormal’ phenomena, which are different from other compositions and other systems, were found. X-ray diffraction (XRD) and scanning electron microscope (SEM) study were performed to investigate the crystalline structure and the microstructure of PSTT ceramics. They revealed that the dielectric and piezoelectric properties of La-doped PSTT strongly depend on the amount and the location of La ions in the samples. A model describing the diffusion of La ions in PSTT during sintering and annealing is proposed. The model agreed well with the XRD analysis results, and explained the effect of La doping on the properties of PSTT.