Dynamical response of localized electron hopping and dipole relaxation in Cu1-xZnxFe2O4 magnetoceramics

We report a detailed study on the dynamical response of localized electron hopping and dipole relaxation in bulk polycrystals of Zn diluted Cuprospinel (Cu1-xZnxFe2O4). The variations in the dielectric dispersion and ac-resistivity (ρac) were analyzed over a wide temperature (77K≤T≤823K) and frequency (20 Hz≤f≤20 MHz) window for a critical composition xc=0.4. The variation of eR(f,T) followed the Maxwell–Wagner type polarization mechanism in-line with the Koops phenomenological theory. Our analysis of ρac(T,f) provide strong evidence to the Mott's variable range hopping of charge transport between the localized states at low temperatures, however, thermally-activated Arrhenius like behaviour was noticed at high temperatures with EA=656 meV for xc=0.4. Moreover, electric modulus spectroscopic studies (M*(f,T)) reveals two distinct types of relaxation phenomena: (i) the short-range oscillations of the charge carriers within the potential well of grains and (ii) the long-range movement of charge carriers across the grain boundaries. The depressed semi-circles of the Nyquist plots and lower values of non-exponential parameter extracted from M*(f,T) suggest the non-Debye type relaxation process present in the system with a widespread distribution of relaxation times. The frequency exponent (s(x,T)) study of Jonscher's power law reveals that the ac-conductivity follows small-polaron tunneling followed by the correlated-barrier-hopping mechanism for x 400K, where thermally activated Arrhenius-type conduction of charge carriers is prevalent in this spinel system. Furthermore, the tetragonally (I41amd) distorted systems (x≤0.05) exhibit less activation energy (EA-VRH) values as compared to those of cubic-spinel symmetry (Fd-3m) which saturates at 130 meV for 0.1≤x≤0.6. Compositional dependent tunability of the above discussed parameters may open a constructive approach to design low energy-loss and high-resistive electromagnetic elements for microwave devices which is the key significance of the present study.