Colossal Dielectric Constant Achieved via Acceptor-Donor doped ZnO Ceramic

Materials having colossal dielectric constant (CDC) and low loss (, ) with good frequency stability is crucial for device miniaturization and high-energy density storage application. Hu et alrecently reported a temperature and frequency independent CDC with a low dielectric loss in acceptor-donor co-doped TiO₂. The CDC is postulated to be originated from electron-pinned defect dipoles which is the acceptor-donor defect complex, though the detail mechanism and experimental evidence are lacking.
Li-Al co-doped ZnO, Zn_0.99(Li_0.1, Al_0.2)_0.033, ceramic exhibits CDC with good frequency stability, which have a dielectric constant ~10⁴at 1 kHz. Impedance spectroscopy shows that the CDC phenomenon is not associated with the internal barrier capacitance (IBLC) effect. M''(f) spectrum obtained from electric modulus () analysis reveals two relaxation processes P1 and P2. Frequency dependent ac conductivity data can be well fitted by the Correlated Barrier Hopping (CBH) model, showing that the CDC would be originated from the thermally activated electron hopping between two neighboring acceptor-donor defect sites over their Columbic barrier. A simple model involving these acceptor-donor defect complex dipoles and the Cole-Davidson distribution of relaxation time can explain the CDC phenomenon.