Impact of Cu2O doping on high dielectric properties of CuO ceramics

Single-phase CuO ceramic samples were prepared with the starting nano powders of CuO + xCu2O (x = 0, 1, 3, 7% in mole ratio) via solid state reaction method, and characterized by X-ray diffraction, Raman scattering and scanning electron microscopy. For all the samples, the temperature dependences of dielectric constants and losses were measured at the frequencies of 102, 103, 104, 105 and 106 Hz, respectively. With increasing doping content of Cu2O, a strong correlation is demonstrated at given temperature and frequency between the measured dielectric constants and the unit-cell volumes of CuO. The strong correlation is argued in terms of the change in densities of CuO defects (e.g. Cu/O vacancies and/or interstitial Cu impurities) due to Cu2O doping, which is supported by the formation energies of CuO defects and the corresponding unit-cell volume from first-principles calculations. The high dielectric constant (∼103-105) of CuO ceramic is therefore attributed to the reduction in resistance due to Cu/O defects in the grain by Maxwell-Wagner mechanism.