Dielectric response of PZN-based MPB composition doped with lanthanum

Dielectric and piezoelectric properties of the lanthanum-doped morphotropic phase boundary (MPB) composition in the Pb(Zn_1/3Nb_2/3)O₃-BaTiO₃-PbTiO ₃ system have been studied. Compositions of the samples were intentionally modified so that the compensation for the charge difference between La³⁺ and Pb²⁺ ions was realized by the increased Zn/Nb ratio. The solid solubility limit of La₂O₃ is shown to be less than 5mol% by X-ray diffraction analysis. Rhombohedral phase is increasingly stabilized against tetragonal phase with progressive incorporation of the dopant into the A-site of perovskite structure, alternatively, the location of the MPB composition range is shifted towards PT-rich end. Moreover, it was revealed that the lattice distortion of either tetragonal or rhombohedral phase can be reduced by La-doping. The dielectric permittivity maximum ε_max′ and the temperature of ε_max′ are remarkably decreased by increasing La₂O₃ content, whilst the degree of the frequency-dispersion is slightly weakened. Both the degree of diffuse phase transition (DPT) and the non-Curie-Weiss behavior can be significantly promoted by La-doping.