Nonlinear impedance as possible result of ion–polaron interaction in Cu2O–Al2O3–SiO2 glass

Nonlinear a.c. impedance measurements were performed in the Cu2O–Al2O3–SiO2 glass in a wide frequency range. The obtained results showed a large nonlinearity observed in the impedance signal at moderate electric fields of an order of 1 V/mm. The contents of the third harmonics reached about 10% and strongly depended on the temperature and frequency. The investigated glass exhibited mixed electronic–ionic conductivity. Electronic conduction occurred by small polaron hopping between Cu+ and Cu2+ ions. On the other hand, the movement of Cu+ ions was responsible for ionic conductivity. We believe that both processes modify each other in a complicated way and the impedance should not be considered linear any more.