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 15K.•For 20, 30 and 40wt% ZnO composites, a high frequency relaxation is detected within the range 104–105Hz, 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 10Hz and is ascribed to space charge relaxation.•Composites loaded with 10wt% 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 10mHz to 1MHz for temperature ranging from 15K to room temperature. Lowering temperature, the dc conductivity was suppressed, revealing underlying dielectric relaxation mechanisms. For pristine polypyrrole and 10wt% ZnO composites, no dielectric relaxation is detectable. For 20, 30 and 40wt% ZnO composites, a relaxation was detected in the vicinity of range 104–105Hz. 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 0.01–10Hz, stemming from space charge polarization. The shift of the relaxation upon temperature provides an insight to the dynamics of relaxing charge entities.