Correlation between resistance degradation and thermally stimulated depolarization current in acceptor (Mg)-doped BaTiO₃ submicrometer fine-grain ceramics

Thermally stimulated depolarization current (TSDC) of acceptor (Mg)-doped BaTiO₃ ceramics was analyzed for submicrometer fine grain specimens. For a fixed condition of polarization field (E_P) and polarization time (t_P), the TSDC associated with an oxygen vacancy relaxation showed two peaks with relaxation temperatures (T_m) under low polarization temperature (T_P) conditions. It is inferred that the TSDC peak of the lower T_m is due to the relaxation of a distributed space charge within a grain and has a short relaxation time constant (τ₀), and the higher T_m is due to the long-range relaxation across grain boundaries with a larger time constant, τ₀. The onset condition for resistance degradation can be correlated with the breaking point of T_P, at which the TSDC peak changes from in-grain relaxation to across-grain boundary relaxation. The breaking point of T_P and the time to degradation systematically decreased with the increase of acceptor concentration. Such behavior can be correlated with the decrease of T_P, T_m, τ₀, and little change of activation energy of relaxation, which is due to the increase of concentration.