A core-shell synthesis of CaCu3Ti4O12 (CCTO) ceramics showing colossal permittivity and low electric losses for application in capacitors

A core-shell synthesis is applied to CaCu3Ti4O12, a material that shows colossal permittivity. The objective was to test several bulk permittivity of the shell material in order to reach a large capacity of the grain boundaries after sintering. The permittivity is improved with certain shells while the bulk resistivity reaches levels approaching that of commercial grain boundary barrier layer (GBBL) ceramic capacitors. The highest permittivity is confirmed to be related to the highest capacity of grain boundaries. The bulk resistivity is related to that of grain boundaries. If one attaches the more important weight to a high bulk resistivity without need of permittivity larger than 15,000, as in commercial GBBL ceramic capacitors, several samples appear convenient. On the other hand, much higher permittivity can be reached like in CCTO with a shell of TiO2 but at the expense of dielectric losses, possibly due to oxygen departure from stoichiometry. Thermal post-treatment under various controlled atmosphere have been applied to reduce dielectric losses.