Influence of Lanthanum on Microstructure and Dielectric Properties of Barium Titanate Ceramics by Solid State Reaction

摘要

La-doped barium titanate ceramics with 0～1.0 at.% La_2O_3 were prepared by conventional solid state reaction method. The crystal structure and dielectric properties of La-doped barium titanate ceramics were investigated. Lanthanum ions have entered the unit cell and substituted for Ba~(2+) ions on the A sites of perovskite structure. The a-axis lattice constant increases and the c-axis lattice constant decreases as lanthanum content increases. Addition of lanthanum leads to the fall of the Curie temperature of La-doped BTO ceramics. There are two different doping mechanisms for La-doped BTO ceramics. The dielectric loss of BTO ceramics with 0.3 at.% La_2O_3 is higher than that of pure BTO ceramics. When lanthanum content is above 0.5 at.%, the dielectric loss of La-doped BTO ceramics decrease with the increasing of lanthanum content. The result of dielectric constant as a function of temperature at different frequencies indicates that La-doped BTO ceramics are not relaxor ferroelectrics but ferroelectrics with diffuse phase transition.