Effect of La Concentration on the Kinetics of the Induced Phase Transition in PbMg1/3Nb2/3O3–25PbTiO3 Transparent Ceramics

The effect of La concentration on the kinetic character of the induced phase transition in PbMg1/3Nb2/3O3–25PbTiO3 ferroceramics is studied. Below the Vogel–Fulcher temperature, the time variations of the permittivity and optical transmittance in electric fields 0 < E < 6 kV/cm are analyzed. It was found that, in an electric field, in La-containing transparent ceramics, the permittivity and optical transmittance sharply decrease with time, which indicates an induced phase transition and an increase in the fraction of the ferroelectric phase. It is shown that, in La-undoped ceramics, the changes in the permittivity in the same fields are much smaller. It is found that the stability of the induced phase depends on the La concentration: the higher this concentration, the lower the stability. The results obtained are explained by both a varying degree of smearing of the phase transition and different sizes of polar regions, which depend on the La concentration.