Colossal dielectric permittivity, reduced loss tangent and the microstructure of Ca 1- x Cd x Cu 3 Ti 4 O 12-2 y F 2 y ceramics.

Ca 1- x Cd x Cu 3 Ti 4 O 12-2 y F 2 y ( x = y = 0, 0.10, and 0.15) ceramics were successfully prepared via a conventional solid-state reaction (SSR) method. A single-phase CaCu 3 Ti 4 O 12 with a unit cell ∼7.393 Å was detected in all of the studied ceramic samples. The grain sizes of sintered Ca 1- x Cd x Cu 3 Ti 4 O 12-2 y F 2 y ceramics were significantly enlarged with increasing dopant levels. Liquid-phase sintering mechanisms could be well matched to explain the enlarged grain size in the doped ceramics. Interestingly, preserved high dielectric permittivities, ∼36 279-38 947, and significantly reduced loss tangents, ∼0.024-0.033, were achieved in CdF 2 codoped CCTO ceramics. Density functional theory results disclosed that the Cu site is the most preferable location for the Cd dopant. Moreover, F atoms preferentially remained close to the Cd atoms in this structure. An enhanced grain boundary response might be a primary cause of the improved dielectric properties in Ca 1- x Cd x Cu 3 Ti 4 O 12-2 y F 2 y ceramics. The internal barrier layer capacitor model could well describe the colossal dielectric response of all studied sintered ceramics.