DIELECTRIC PROPERTIES OF La/Mn CODOPED BARIUM TITANATE CERAMICS

La/Mn codoped BaTiO3 ceramics with different La2O3 content, ranging from 0.3 to 1.0 at% La, together with undoped BaTiO3,were investigated regarding their microstructure and dielectric properties. The content of MnO2 kept constant at 0.01 at% Mn in all investigated samples. La/Mn codoped and undoped BaTiO3 were obtained by a modified Pechini method and sintered in air at 13000C for two hours.The homogeneous and completely fine-grained microstructure with average grain size from 0.3 to 1mm 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 permittivity and dissipation factor were investigated as a function of frequency and temperature. Dielectric permittivity of doped BaTiO3 was in the range of 3945 to 12846 and decreases with increase of additive content. The highest value of dielectric constant at room temperature (er= 12846) and the greatest change at Curie temperature (er= 17738) were measured in 0.3at% La doped samples. Dissipation factor was range from 0.07 to 0.62 for all investigated samples. The Curie constant (C) and Curie-Weiss temperature (T0) together with critical exponent of nonlinearity (g) were calculated using a Curie-Weiss and modified Curie-Weiss law. The Curie constant increase with increasing dopant content and the highest values were measured in 1.0 La doped samples. The obtained values of g is in the range from 1.04 to 1.53 and pointed out the sharp phase transformation from ferroelectric to paraelectric phase at Curie temperature