Origin of dielectric relaxation observed in complex perovskite oxides Ba(1-x)La(x)Ti(1-x)Cr(x)O3

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Frequency dependence of the dielectric constant of complex perovskite oxide Ba(1-x)La(x)Ti(1-x)Cr(x)O3 (BLTC) ceramics with the composition ratio 0.4<= x <= 0.7 is precisely measured in the temperature range from 20 K to 300 K, and the dielectric relaxation is found to be quite similar to that of CaCu3Ti4O12 (CCTO), which exhibits the Debye-like frequency dispersion around 100 K. In BLTC, the ferroelectric phase transition temperature shifts to lower temperature with increase of x, while a remarkable dielectric relaxation newly appears at higher temperature region. The dielectric relaxation can be explained by an equivalent model of a series of two R-C parallel circuits, which corresponds to a heterogeneous structure in the sample with an internal barrier layer capacitor. Temperature and frequency dependences of the measured dielectric constant are explained well by the model with the temperature-dependent electrical conductivity and temperature-independent intrinsic dielectric constant. It is also found that the contribution of thin layer to the dielectric relaxation in a high temperature region is affected by the dc bias field on the sample.