Grain Boundaries of Semiconducting SrTiO3 and BaTiO3 Ceramics Synthesized from Surface-Coated Powders

The chemical and electrical features of the grain boundaries in polycrystalline SrTi_0.99Nb_0.01O₃ (ST) and BaTiO₃ (BT) ceramics, which were synthesized by hot-press sintering Na- and Mn-coated semiconducting ST and BT powders, respectively, were investigated. Because of the excess negative electric charges formed near grain boundaries, electrostatic potential barriers were formed near the grain boundaries. The electrical features of the grain boundaries in ceramics are very sensitive to the amount of the coating material. When the amount of the coating material was increased from 0 to 5 wt%, the threshold voltage of the ST ceramics and the resistivity jump ratio of the BT ceramics increased from 0.7 to 81.0 V/cm and from 1.0 to 2.0 × 10³, respectively. The electrical features of the grain boundaries are related to their chemical characteristics.