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 epsilon(rRT), dielectric loss tan delta(RT) and the maximum relative dielectric constant epsilon(rmax) decreased and then increased with the increasing non-stoichiometric level. With the increase of La2O3 doping content, the relative dielectric constant epsilon(rRT) increased initially and then decreased. The maximum relative dielectric constant epsilon(rmax) can be increased by applying low doping content of La2O3 in Ti-rich barium strontium titanate ceramics due to the increased spontaneous polarization.