Enhancing giant dielectric properties of Ta5+-doped Na1/2Y1/2Cu3Ti4O12 ceramics by engineering grain and grain boundary

Various strategies to improve the dielectric properties of ACu(3)Ti(4)O(12) (A = Sr, Ca, Ba, Cd, and Na1/2Bi1/2) ceramics have widely been investigated. However, the reduction in the loss tangent (tan delta) is usually accompanied by the decreased dielectric permittivity (epsilon '), or vice versa. Herein, we report a route to considerably increase epsilon ' with a simultaneous reduction in tan delta in Ta5+-doped Na1/2Y1/2Cu3Ti4O12 (NYCTO) ceramics. Dense microstructures with segregation of Cu- and Ta-rich phases along the grain boundaries (GBs) and slightly increased mean grain size were observed. The samples prepared via solid-state reaction displayed an increase in epsilon ' by more than a factor of 3, whereas tan delta was significantly reduced by an order of magnitude. The GB-conduction activation energy and resistance raised due to the segregation of Cu/Ta-rich phases along the GBs, resulting in a decreased tan delta. Concurrently, the grain-conduction activation energy and grain resistance of the NYCTO ceramics were reduced by Ta5+ doping ions owing to the increased Cu+/Cu2+, Cu3+/Cu2+, and Ti3+/Ti4+ ratios, resulting in enhanced interfacial polarization and epsilon '. The effects of Ta5+ dopant on the giant dielectric response and electrical properties of the grain and GBs were described based on the Maxwell-Wagner polarization at the insulating GB interface, following the internal barrier layer capacitor model.