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 CaCu ₃ Ti ₄ O ₁₂ 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.

Electric field stress concentration is one of the causes of partial discharge in power modules, which threatens the power modules’ safe operation. Herein, this paper investigates the influences of temperature (from 150°C to 250°C) and operation duration on the maximum electric field stress at the triple point (silicone elastomers, ceramic, and copper). It reveals that the maximum electric field stress rises with the increase of temperature, while the maximum electric field first increases but then decreases along the operation duration, especially under low temperature. Both the influences of temperature and the operation duration are related to the permittivity (dominated by the relaxation of Si-O bonds), low frequency dispersion phenomenon, and dc conductivities of silicone elastomers, which can be manipulated to suppress electric field stress concentration. This paper provides a method to accurately calculate the electric field. The results are also critical to evaluation and improvement of power modules’ insulation.

In this paper, taking aluminum hydroxide (ATH) filled silicone rubber as a model composite, we report the “n-shape” dynamic electrical conductivity during isothermal crystallization in nonconductive particles filled insulating polymers. During the initial crystallization, rapid growth of dominant lamellae blocks the transport path of impurity ions, contributing to the remarkable reduction of conductivity. Addition of ATH fillers could reduce the silicone rubber content and randomness of crystals formation, lessening the amplitude of decreased conductivity. Afterward, the silicone rubber composites further shrink due to the development of subsidiary lamellae. It results in low activation energy of ion migration and thereby enhances conductivity, whose amplitude is positively related to the crystalline phase. Finally, continuous growth of rigid amorphous fraction with reduced chain mobility impedes the ions transport, decreasing the conductivity again. The growth of rigid amorphous fraction is accelerated in silicone rubber with more ATH fillers because of more constraint of ATH on molecular chains. Our findings afford a simple means to manipulate insulation performance of nonconductive particles filled semi-crystalline polymers and provide a guideline for their use in real operation.

In numerical solutions of Hanai equation widely used in heterogeneous systems, the uncertainty of conductivity at high frequency affects the accuracy of phase parameters results (permittivity and conductivity of components). To overcome this limitation, broadband dielectric spectroscopy of eight groups of silicone rubber (SR) was measured at a frequency from 10 ⁻¹ Hz to 10 ⁵ Hz and at a temperature from 0 °C to −40 °C. An obvious relaxation peak related to the interface between aluminium hydroxide (ATH) and SR was observed and confirmed. Based on the interfacial polarization, phase parameters of ATH and SR were calculated by modified numerical solutions, which was verified by other information. It was found that with the increase of ATH concentration, polarization strength increased and relaxation time decreased, which indicated that the number of charges accumulated at the interface increased in interfacial polarization process and the Debye length of interface decreased. Because of the surface conductivity around ATH, the conductivity of ATH is higher than that of SR. This paper is beneficial for the studies on the interface properties of ATH filled silicone rubber and provides supports for studying the electrical parameters of particles dispersed in continuous medium systems without physical transition or chemical changes with enhanced accuracy.