Study of TiO₂ on the Voltage Holdoff Capacity of Cr/Mn-Doped Al₂O₃ Ceramic in Vacuum

With the development of vacuum electronic devices toward high power, high frequency, and miniaturization, the voltage holdoff capacity of the insulation materials in devices has also been raised to a higher demand. Cr/Mn/Ti-doped Al₂O₃ ceramics were prepared, and the bulk density, micromorphology, phase composition, resistivity, secondary electron emission coefficient, and surface flashover threshold in the vacuum of the Al₂O₃ were characterized. The results show that the addition of TiO₂ to the Al₂O₃ ceramic can promote the sintering of the ceramic. The Cr/Mn/Ti-doped Al₂O₃ ceramic with a homogeneous microstructure can be obtained by an appropriate amount of TiO₂ addition. In the process of the heat treatment, the TiO₂ in the ceramics was reduced to a certain degree, which had an impact on the microstructure of the Al₂O₃ ceramic. Adding a small amount of TiO₂ can improve the voltage holdoff performance in the vacuum. The value of the surface flashover threshold in the vacuum of the Cr/Mn/Ti-doped Al₂O₃ ceramic containing 1 wt.% TiO₂ reached a value of 33 kV, which is 32% higher than that of the basic Al₂O₃ ceramic. The preparation of Al₂O₃ ceramics with a high voltage holdoff capacity in a vacuum provides fundamental technical support for the development of vacuum electronic devices.