Grain size independence of giant dielectric permittivity of CaCu3Ti4−xScxO12 ceramics

The dielectric and electrical properties of CaCu3Ti4−xScxO12 (x=0, 0.04, 0.08, and 0.20) ceramics prepared by a solid-state reaction method were investigated. Grain sizes of CaCu3Ti4O12 were greatly reduced by doping with Sc3+. Surprisingly, the dielectric constant of CaCu3Ti4−xScxO12 ceramics with x=0−0.08 largely increased as the mean grain size decreased. This behavior was extremely hard to produce in CaCu3Ti4O12 ceramics. The nonlinear current−voltage properties CaCu3Ti4−xScxO12 ceramics were significantly degraded. The grain boundary (GB) resistance decreased with increasing Sc3+ concentration even though the density of GB layer increased. This resulted in enhancement of a low-frequency loss tangent due to increased dc conduction. Substitution of some Sc3+ ions into Cu sites was proposed as the cause of reduction of the potential barrier height at GBs. The possible mechanisms of giant dielectric response in CaCu3Ti4O12 ceramics are discussed.