Colossal permittivity due to electron trapping behaviors at the edge of double Schottky barrier

Abstract

Achieving frequency- and temperature-independent colossal permittivity (CP) with low dielectric loss is a long-standing challenge for electronic materials, in which the basic issue is understanding the underlying relaxation mechanism. In this paper, taking CaCu3Ti4O12 ceramics as an example, CP was ascribed to electron-trapping behaviors at the edge of a double Schottky barrier (DSB). On the one hand, the widely reported origins of CP, i.e. Maxwell–Wagner relaxation and polaronic relaxation, were identified as two aspects of the same bulk conductivity. This caused the insights derived from the commonly employed impedance and admittance spectra to be revisited. On the other hand, hysteresis between CP and external voltages at low temperatures, which was caused by electron filling of interface states, was predicted and experimentally confirmed. This further supported the proposal that CP arose from electron trapping at the DSB. Moreover, multiple relaxations were foreseen when more than one kind of point defect existed in the depletion layers of a DSB. The establishment of intense ‘effective’ relaxation, which was related to shallow traps, was indispensable for achieving CP, while ‘redundant’ relaxation was induced by deep-level defects, resulting in relatively high dielectric loss. Therefore, proper manipulation of the DSB and its related defect structures was crucial for achieving stable CP with sufficiently low dielectric loss.