Structural Model of Planar Defects in CaCu 3 Ti 4 O 12 Exhibiting a Giant Dielectric Constant

It is known that the unusually large dielectric constant in single crystals of CaCu 3 Ti 4 O 12 (CCTO) requires the existence of barrier layers in the form of twin boundaries or planar defects within the crystals, and even the high dielectric constant of ceramic CCTO samples requires one to consider domain boundaries within the crystallites. As a probable origin of such domain boundaries, we proposed a structural model of plane defect that can result from a twinning parallel to the (100), (010), and (001) planes and examined its local electronic structures. This plane defect model provides a plausible microscopic explanation for the origin of gigantic dielectric constants in CCTO.