Dielectric response of lanthanum-modified Pb(Fe_1/2Ta _1/2)O₃ relaxor ferroelectrics

In this paper, the dielectric response of lanthanum-modified Pb(Fe _1/2Ta_1/2)O₃ relaxor ferroelectrics is studied. La ions are intended to replace Pb ions (A-site) of perovskite structural block where the electrical neutrality is maintained via the generation of negatively charged B-site vacancies. XRD examination shows that predominantly single-phase can be achieved using the one-step preparation approach throughout the entire range of doping. A peak dielectric permittivity maximum (ε′ _max) at slight doping (0.3mole% La₂O₃) is observed, origin of which is discussed. Addition of La₂O₃ lowers the Curie temperature (T_max) whereas the frequency-dispersion of ε_max′ is found to be hardly affected implying the ferroelectric couplings among oxygen octahedra being nearly unaltered. The paraelectric to ferroelectric phase transition, however, can be rendered increasingly broader by La-doping, among which the 0.3mole% La₂O ₃ addition exhibits the most prominent effect.