Influence of Rare-Earth Additives (La, Sm and Dy) on the Microstructure and Dielectric Properties of Doped BaTiO3 Ceramics

A series of La/Mn, Sm/Mn and Dy/Mn codoped BaTiO3 samples were prepared by the conventional solid state procedure with dopant concentrations ranging from 0.1 up to 2.0 at%. The specimens were sintered at 1320 degrees C and 1350 degrees C in an air atmosphere for two hours. The low doped samples demonstrated a mainly uniform and homogeneous microstructure with average grain sizes ranging from 0.3 mu m to 5.0 mu m. The appearance of secondary abnormal grains in the fine grain matrix and core-shell structure were observed in highly doped La/BaTiO3 and Dy/BaTiO3 sintered at 1350 degrees C. The low doped samples, sintered at 1350 degrees C, display a high value of dielectric permittivity at room temperature, 6800 for Sm/BaTiO3, 5900 for Dy/BaTiO3 and 3100 for La/BaTiO3. A nearly flat permittivity-response was obtained in specimens with 2.0 at% additive content. Using a modified Curie-Weiss law the Curie-like constant C' and a critical exponent gamma were calculated. The obtained values of gamma pointed out the diffuse phase transformation in heavily doped BaTiO3 samples.