Colossal permittivity behavior and its origin in rutile (Mg_1/3Ta_2/3)_xTi_1-xO₂

This work investigates the synthesis, chemical composition, defect structures and associated dielectric properties of (Mg²⁺, Ta⁵⁺) co-doped rutile TiO₂ polycrystalline ceramics with nominal compositions of (Mg²⁺_1/3Ta⁵⁺_2/3)_xTi_1-xO₂. Colossal permittivity (>7000) with a low dielectric loss (e.g. 0.002 at 1 kHz) across a broad frequency/temperature range can be achieved at x = 0.5% after careful optimization of process conditions. Both experimental and theoretical evidence indicates such a colossal permittivity and low dielectric loss intrinsically originate from the intragrain polarization that links to the electron-pinned Mg_Ti″ + V_O^•• + 2Ta_Ti^• + 2Ti_Ti′ defect clusters with a specific configuration, different from the defect cluster form previously reported in tri-/pent-valent ion co-doped rutile TiO₂. This work extends the research on colossal permittivity and defect formation to bi-/penta-valent ion co-doped rutile TiO₂ and elucidates a likely defect cluster model for this system. We therefore believe these results will benefit further development of colossal permittivity materials and advance the understanding of defect chemistry in solids.