Origin of Giant Dielectric Response in Nonferroelectric CaCu 3 Ti 4 O 12 : Inhomogeneous Conduction Nature Probed by Atomic Force Microscopy

Local probing of conduction behaviors using atomic force microscopy clearly shows that the grain boundary of polycrystalline CaCu 3 Ti 4 O 12 is semiconducting. In contrast, the grain is a mixture of semiconducting and insulating regions. This inhomogeneous conductive feature leads to giant dielectric response in CaCu 3 Ti 4 O 12 . Theoretical analysis demonstrates that the dielectric response follows a typical Debye-type relaxation, and its unusual temperature dependence originates from the thermal activation behavior of free carries within the semiconducting regions in the grain. An effective way to control the electrical properties of CCTO is to control the defect density within a grain rather than the grain boundary.