Transition of the colossal permittivity related dielectric relaxation in V-doped CaCu₃Ti₄O₁₂ceramics

The co-achieving of stable colossal permittivity (CP) and low dielectric loss in dielectric materials has been a challenge. In this paper, a transition in CP was observed in V-doped CaCu3Ti4O12 (CCTO) ceramics. The fast high-frequency dielectric relaxation that mainly contributed to CP of CCTO ceramics was greatly suppressed in V-doped CCTO samples. Its relaxation activation energy remained ∼0.10 eV, while its magnitude dropped from thousands in CCTO to dozens in V-doped CCTO. Instead, CP of V-doped CCTO ceramics mainly arose from another slow dielectric relaxation, which appeared in a much lower frequency range. Moreover, this dielectric relaxation gradually turned from a "carrier-dominated"relaxation into a "dipole-dominated"one with the increase in temperature. Its relaxation activation energy also changed from ∼0.06 to 0.42 eV in the meanwhile. These results indicated important roles of multiple point defects and their relating charge transport in CP behaviors. It supported that CP arose from electron trapping behaviors at the edge of double Schottky barriers at grain boundaries. On this basis, suppression of any deep-level point defects was concluded to be a potential clue to achieve both stable CP and sufficiently low dielectric loss in CCTO ceramics and other CP materials.