Interfacial and space charge dielectric effects in Polypyrrole/Zinc Oxide composites

•Polypyrrole/zinc oxide composites investigated by complex permittivity measurements at isothermal conditions from room temperature to 15 K.•For 20, 30 and 40 wt% ZnO composites, a high frequency relaxation is detected within the range 104-105 Hz, in accordance with theoretical predictions for interfacial polarization.•On increased ZnO loading, an additional low-frequency relaxation appears about the frequency range 10−2 to 10 Hz and is ascribed to space charge relaxation.•Composites loaded with 10 wt% ZnO are most proper optoelectronic material for electric charge percolation, due to their combined good electrical conduction, poor capacitance effects.

Polypyrrole/zinc oxide composites were studied by broadband dielectric spectroscopy in the frequency range 10 mHz to 1 MHz for temperature ranging from 15 K to room temperature. Lowering temperature, the dc conductivity was suppressed, revealing underlying dielectric relaxation mechanisms. For pristine polypyrrole and 10 wt% ZnO composites, no dielectric relaxation is detectable. For 20, 30 and 40 wt% ZnO composites, a relaxation was detected in the vicinity of range 104-105 Hz. Its typical mean relaxation time and its concentration dependence are compatible with Sillar's model for interfacial polarization in heterogeneous matter consisting of inclusions dispersed within a dielectric matrix. At high ZnO concentration, a low-frequency relaxation also appeared around 0.01-10 Hz, stemming from space charge polarization. The shift of the relaxation upon temperature provides an insight to the dynamics of relaxing charge entities.