Colossal Dielectric Behavior and Dielectric Relaxation of (Li, Fe) Co-Doped ZnO Ceramics

The co-doped ceramics (Fe_0.5Li_0.5)_xZn_1−xO (x = 0.005, 0.01, 0.015) (abbreviated as FL-0.005, FL-0.01, and FL-0.015) as well as the Fe-only and Li-only (abbreviated as Fe-0.01 and Li-0.01) doped samples are prepared by a solid-state reaction method to investigate their colossal dielectric property for the first time. The permittivity value (ɛ′ ≈ 2.05 × 10⁴ at 20 °C, 1 kHz with tanδ ≈0.61) is the highest in co-doped ZnO ceramics reported so far. The colossal permittivity is brought out by the step-like dielectric abnormities over which ɛ′ goes up steeply (≈10¹–≈10⁴) resulting from the mix-valent ions of Fe²⁺/Fe³⁺, while the grain boundaries tend to make the dominant contribution at elevated temperature above the step-like abnormity. The defect-dipole (Li⁺–Fe³⁺) can localize the electrons to a certain extent in the ZnO matrix inducing effective suppression of the dielectric loss. The sample FL-0.01 exhibits the optimal colossal dielectric property and as x goes up further, the dielectric loss tends to increase obviously. This work provides a new routine to design optimal colossal dielectric materials and related devices for research and applications.