Functionally
graded materials (FGMs) exhibit unique properties
and are expected to deliver outstanding and stable performance under
extreme conditions. High-voltage, high-power FGM-based electric insulation
commonly fails because of inadequate surface charge control (flashover)
performance and stability of stacked layers of dielectric materials
with graded permittivity εr. Here, we address these
issues by interfacing the rutile and anatase TiO2 layers
on a ceramic with very different εr values of 110,
48, and 9, respectively, using scalable, environment-benign, and energy-efficient
atmospheric pressure plasma processing. The FGM drastically reduces
the maximum electric field along the optimized surface by 66% and
increases surface flashover voltage by 36 %, while featuring a remarkable
(120/180 days) long-term stability. The mechanisms of the plasma-enabled
graded layer formation are presented, which can be used for precise
engineering of FGMs for diverse applications in other fields.