Unveiling of interstice-occupying dopant segregation at grain boundaries in perovskite oxide dielectrics for a new class of ceramic capacitors

When aliovalent foreign cations are doped into ABO(3)-type perovskite oxides, they are usually substituted for either dodecahedral A or octahedral B sites, depending on their relative ionic size. In addition, their effective charge can be ionically compensated through the creation of positively charged oxygen vacancies for acceptor doping and negatively charged cation vacancies for donor doping. In stark contrast to this well-known substitutional doping in perovskite oxides, we directly uncover the presence of indium dopants occupying square-planar interstices and charge-compensating Ba vacancies at grain boundaries in polycrystalline BaTiO3. Moreover, this significant chemical heterogeneity by the defect combination of In cations and Ba vacancies at grain boundaries appears to provide a substantial barrier impeding grain-boundary migration during sintering. The highly densified fine-grain microstructure attained by strong inhibition of grain growth in In-added BaTiO3 enables unprecedented dielectric properties, encompassing remarkably low dissipation loss and DC-field-insensitive and temperature-independent high permittivity, applicable to multilayer ceramic capacitors. Breaking the conventional wisdom on the utilization of multiple additives, the present study emphasizes that the suppression of grain growth and the control of additive segregation at the atomic level are key approaches toward achieving better reliability in ceramic capacitors.

Automated summary

When foreign cations are doped into ABO(3)-type perovskite oxides, they usually replace A or B sites depending on their ionic size. This study uncovers the presence of indium dopants occupying square-planar interstices and charge-compensating Ba vacancies at grain boundaries in polycrystalline BaTiO3. This chemical heterogeneity inhibits grain-boundary migration and enables the attainment of fine-grain microstructures with unprecedented dielectric properties.