Colossal dielectric permittivity, reduced loss tangent and the microstructure of Ca1-xCdxCu3Ti4O12-2yF2y ceramics

Ca1-xCdxCu3Ti4O12-2yF2y (x = y = 0, 0.10, and 0.15) ceramics were successfully prepared via a conventional solid-state reaction (SSR) method. A single-phase CaCu3Ti4O12 with a unit cell similar to 7.393 angstrom was detected in all of the studied ceramic samples. The grain sizes of sintered Ca1-xCdxCu3Ti4O12-2yF2y 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, similar to 36 279-38 947, and significantly reduced loss tangents, similar to 0.024-0.033, were achieved in CdF2 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 Ca1-xCdxCu3Ti4O12-2yF2y ceramics. The internal barrier layer capacitor model could well describe the colossal dielectric response of all studied sintered ceramics.