The Mechanism of DC Breakdown of EP/TiO2Nanocomposites at Elevated Temperature

The decreased breakdown strength of epoxy composites as a function of temperature poses a possible hazard to the safe functioning of electrical and power electronic equipment and hinders the downsizing of advanced equipment. In this study, the chain dynamics and carrier transport parameters were characterized by dielectric spectrum, thermal expansion coefficients, and thermally stimulated current, and the DC breakdown mechanism of epoxy resin (EP)/TiO
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nanocomposites at temperatures ranging from 303 K to 433 K was investigated using a breakdown simulation model based on charge transport and molecular chain dynamics equations. The results reveal that the temperature-dependent breakdown strength of EP/TiO
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nanocomposites is split into two zones. 1) Below the glass transition temperature, the synergistic effects of carrier migration and segmental dynamics dominate DC breakdown. 2) In the temperature range above the glasstransition temperature: the DC breakdown is governed by the free volume expansion generated from the backbone dynamics. The breakdown strength falls drastically with increasing temperature and free volume expansion. Near glass-transition temperature, the dominant mechanism of breakdown strength changes from segmental dynamics to backbone dynamics. This work results give a theoretical foundation for the development of power electronics and electronic equipment.