Achieving ultrahigh dielectric breakdown strength in MgO-based ceramics by composite structure design

The pursuit of electronic materials and devices with high dielectric breakdown strength (DBS), and the clarification of the dielectric breakdown mechanism are of great importance to scientific research and industry applications. Among the numerous material systems, MgO has great potential due to its simple crystal structure and wide band-gap together with favorable physical properties, while its sintering behavior at high temperature turns out to be an obstacle for high DBS and its breakdown mechanism remains to be studied. On the basis of these concepts, simple (1 − x)MgO–xAl2O3 dielectric ceramics were designed and prepared via a solid-state reaction method, and a 0–3 composite structure was obtained. An ultrahigh DBS was achieved in 0.92MgO–0.08Al2O3 with 126.4 kV mm−1 (0.5 mm in thickness and 8 mm in diameter), which is the highest value reported for bulk ceramics. Systematic research shows that the improvement of DBS is ascribed to a conversion from the electrical breakdown model to the thermal breakdown model, which could be explained by microstructure evolution, enhanced mechanical properties and relevant thermal properties. Meanwhile, complex impedance spectroscopy measurement reveals that the introduction of Al2O3 into MgO can obviously enhance the resistivity and activation energy, which is also beneficial to enhance the DBS. More importantly, this work not only opens up a new research and application field (such as high voltage equipment and electronic device application) for novel MgO-based ceramics, but also systematically expounds on the intrinsic mechanism of structural design to enhance the DBS.