DIELECTRIC PROPERTIES OF La/Mn CODOPED BARIUM TITANATE CERAMICS

La/Mn codoped BaTiO3 ceramics with various La2O3 content, ranging from 0.3 to 1.0 at% La, were investigated regarding their microstructure and dielectric properties. The content of MnO2 was kept constant at 0.01 at% Mn in all samples. La/Mn codoped and undoped BaTiO3 were obtained by a modified Pechini method and sintered in air at 1300 degrees C for two hours. The homogeneous and completely fine-grained microstructure with average grain size from 0.5 to 1.5 mu m was observed in samples doped with 0.3 at% La. In high doped samples, apart from the fine grained matrix, the appearance of local area with secondary abnormal grains was observed. The dielectric properties were investigated as a function of frequency and temperature. The dielectric permittivity of the doped BaTiO3 was in the range of 3945 to 12846 and decreased with an increase of the additive content. The highest value for the dielectric constant at room temperature (epsilon(r)= 12846) and at the Curie temperature (epsilon(r) = 17738) were measured for the 0.3 at% La doped samples. The dissipation factor ranged from 0.07 to 0.62. The Curie constant (C), Curie-Weiss temperature (T-0) and critical exponent (gamma) were calculated using the Curie-Weiss and the modified Curie-Weiss law. The highest values of Curie constant (C= 3.27. 10(5) K) was measured in the 1.0 at% La doped samples. The obtained values for. ranged from 1.04 to 1.5, which pointed out the sharp phase transformation from the ferroelectric to the paraelectric phase.