The (1 − x)BaTiO3–x(Bi3/4Na1/4)(Mg1/4Ti3/4)O3 (0.2 ≤ x ≤ 0.9) ceramics were prepared by conventional solid-state reaction route. Their dielectric properties were found to follow a modified Curie–Weiss law and an empirical Lorenz-type relation in respective temperature regions. Their dielectric relaxation times fit well with the Vogel–Fulcher relation for x = 0.2, 0.3, and 0.4. For x = 0.5, 0.6, 0.7, and 0.8, however, the fitting curves of Vogel–Fulcher relation showed certain deviation from the experimental data. Based on the theoretical treatment of Landau–Ginsburg–Devonshire theory, an approximate treatment of the E-field dependence of the permittivity was adopted and found to describe well the field dependence of the permittivity for x = 0.3 at temperatures equal to and below Tm (temperature of maximum dielectric permittivity). A combined Langevin-type expression used in the present work appears to give a good account for the field dependence of the permittivity, assuming polar regions are of a statistical cluster size. For polar clusters of linear dimension L ~ 4–8 nm for instance, the fitted values of polarization are in the range of P ~ 6.2–9.8 μC/cm2.
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This work has been supported by US National Science Foundation under grant number NSF 0833000 and by US Office of Naval Research under grant number N00014-08-1-0854. One of the authors acknowledges the support of National Natural Science Foundation of China (Project 50772087) and scholarship from China Scholar Council through the program of National study-abroad project for postgraduates of high level universities.