Dynamical Response Of Localized Electron Hopping And Dipole Relaxation In Cu1-X Zn (X) Fe2o4 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 - x Zn (x) Fe2O4). The variations in the dielectric dispersion and ac-resistivity (rho (ac) ) were analyzed over a wide temperature (77 K <= T <= 823 K) and frequency (20 Hz <= f <= 20 MHz) window for a critical composition x (c) = 0.4. The variation of epsilon R (f, T) followed the Maxwell-Wagner type polarization mechanism in-line with the Koops phenomenological theory. Our analysis of rho (ac) (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 E (A) = 656 meV for x (c) = 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 tunnelling followed by the correlated-barrier-hopping mechanism for x < = x (c) reorientational hopping mechanism is predominant, except for T > 更多