Microstructure and dielectric properties of La2O3 doped Ti-rich barium strontium titanate ceramics for capacitor applications

Microstructure and dielectric properties of La₂O₃ doped Ti-rich barium strontium titanate ceramics, prepared by solid state method, were investigated with non-stoichiometric level and various La₂O₃ content, using XRD, SEM and LCR measuring system. With an increase of non-stoichiometric level, the unit cell volumes of perovskite lattices for the single phase Ti-rich barium strontium titanate ceramics increased due to the decreasing A site vacancy concentration V″_A. The unit cell volume increased and then decreased slightly with the increasing La₂O₃ content. Relatively high non-stoichiometric level and high La₂O₃ content in Ti-rich barium strontium titanate ceramics contributed to the decreased average grain size as well as fine grain size distribution, which correspondingly improved the temperature stability of the relative dielectric constant. The relative dielectric constant є_rRT, dielectric loss tanδ_RT and the maximum relative dielectric constant є_rmax decreased and then increased with the increasing non-stoichiometric level. With the increase of La₂O₃ doping content, the relative dielectric constant є_rRT increased initially and then decreased. The maximum relative dielectric constant є_rmax can be increased by applying low doping content of La₂O₃ in Ti-rich barium strontium titanate ceramics due to the increased spontaneous polarization.