Influence of Sn and F dopants on giant dielectric response and Schottky potential barrier at grain boundaries of CCTO ceramics

Abstract The applicability of CaCu3Ti4O12 (CCTO) ceramics in modern microelectronics has been widely investigated; however, CaCu3Ti4O12 suffers large loss tangents, which limits its applicability. We employed a solid-state reaction method to prepare a new cation–anion codoping system incorporating Sn and F ions that can reduce the loss tangent and improve the electrical properties of CaCu3Ti4O12 ceramics. The microstructure, dielectric response, nonlinear current–voltage characteristics, and electrical properties of the grains and grain boundaries of the (Sn–F) codoped CCTO ceramics (SF-CCTO) were investigated. Sn strongly suppressed the grain growth by reducing the grain boundary mobility, while F enhanced the densification of the sintered ceramics. Both the dielectric permittivity and loss tangent of the SF-CCTO ceramics tended to decrease with decreasing mean grain size owing to the increased codopant concentration. Notably, a large dielectric permittivity of ~3 × 104 with a low loss tangent of ~0.5 was achieved. Moreover, the breakdown electric field of the SF-CCTO ceramic was increased from ~200 V/cm (for the undoped CCTO ceramic) to ~200 V/cm. The Schottky barrier height at the grain boundary was enhanced by doping CaCu3Ti4O12 with Sn and F ions. The reduced loss tangent and enhanced nonlinear electrical properties were attributed to the significant increase in the total grain boundary resistance resulting from the reduced mean grain size and the increased potential barrier height. The nonlinear electrical properties and dielectric behavior is well described in terms of the internal barrier layer capacitor structure using the Maxwell–Wagner relaxation model. This method may be applied to other polycrystalline ceramics to improve their dielectric and nonlinear electrical properties.