Dynamical response of localized electron hopping and dipole relaxation in Cu_1 − x Zn _x Fe₂O₄ magnetoceramics

Abstract

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 (ρ 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 R (f, T) followed the Maxwell–Wagner type polarization mechanism in-line with the Koops phenomenological theory. Our analysis of ρ 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 0.1. However, for x ≥ x c reorientational hopping mechanism is predominant, except for 400 K, where thermally activated Arrhenius-type conduction of charge carriers is prevalent in this spinel system. Furthermore, the tetragonally (I41/amd) distorted systems (x ≤ 0.05) exhibit less activation energy (E A − 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.

Correlated barrier charge hopping and non-Debye relaxation in columbite MnNb2O6

“…These plots yield the magnitude of exponents 's 1 and s 2 ' and σ dc for various temperatures from 173 K to 473 K. The obtained exponents 's 1 and s 2 ' are plotted against temperature in figure 7, from this figure it is clear that the magnitude of exponent s 1 decreases from 1.03 to 0.03 and the exponent s 2 decreases from 2.00 to 0.19 as the temperature increases from 173 K to 473 K, respectively. This behaviour is in-line with those systems which exhibit the CBH conduction mechanism (according to CBH the magnitude of s must decrease with temperature) [33,43]. Existence of similar type of CBH conduction mechanism and the decreasing trend of the exponents 's 1 ' and 's 2 ' with temperature have been observed in several perovskite and spinel oxides such as La 0.9 Sr 0.1 MnO 3 [44], BaZr 0.1 Ti 0.9 O 3 [45] and MgCr 2 O 4 [46].…”

“…The linear variation of ρ ac T supports the Arrhenius behaviour indicating the thermally activated charge transport mechanism prevails in MnNb 2 O 6 system. Further, the linear fit provides the activation energy, E ac = 0.444 eV for 1 kHz and it starts to deviate for T < 300 K, giving us a signature of different conduction mechanisms at lower temperatures [23,32,33],…”

“…In the low frequency regime, the dc-conductivity σ dc (obtained from the Double power law) increases with increasing temperature due to thermally activated charge carriers. For T > 300 K the dc-conductivity follows the Arrhenius relation given below [33,48];…”

Crystal structure, optical characterization, conduction and relaxation mechanisms of a new hybrid compound (C6H9N2)2[Sb2Cl8]

“…With the help of this illustration, two distinct linear dielectric responses are visible corresponding to the contribution of the bulk and grain boundaries, which are represented by the segments marked with the letters A and B and the borderline frequency f = 1258 Hz, respectively. 55,56…”

Slow spin dynamics of cluster spin-glass spinel Zn(Fe 1−x Ru x )2O4: role of Jahn–Teller active spin-1/2 Cu2+ ions at B-sites

“…Spinel-ferrites are well-studied systems in the scientific literature because of their unique electrical and magnetic properties which largely depend upon the nature of substituents at the tetrahedral-A or octahedral-B sites [1,2]. Consequently, a wide variety of ferrite families have been investigated since decades both from a theoretical and an experimental point of view and their full potential towards the applications in the fields of microwave devices, circulators/actuators, semi-transparent magnetic semiconductor with high Curie temperature, and sensors is being explored [3][4][5][6]. Enormous research activity is still in progress on the low-dimensional nanostructures of these compounds, especially focusing on their catalytical activity and role in fuel-cells, Li-ion batteries and in the renewable energy sectors [7][8][9][10][11][12].…”