Charge carrier localization in investigated by ac conductivity measurements

Abstract

We have investigated the complex ac conductivity of for , temperatures and frequencies . In addition, results from dc measurements are presented. From the frequency dependence of the complex conductivity we find hopping of Anderson-localized charge carriers as the dominant transport process in certain temperature and composition ranges. We deduce that, while Anderson localization is not the driving mechanism for the metal-insulator transition observed in this compound, it is responsible for the high-resistivity regions observed at low doping levels and low temperatures. The results indicate a polaronic nature of the charge carriers. From the temperature dependence of the ac conductivity and the magnetic permeability, deduced in the skin-effect-dominated regime, various phase transition temperatures have been determined.

Polaron relaxation and hopping conductivity inLaMn1−xFexO3

“…The UDR and SU contributions to the intrinsic ac conductivity in the present investigation is consistent with the results for single crystal of LaMnO 3 reported by Seeger et al 15 Since UDR contribution to the ac conductivity is found in a very small region of the frequency, a large error is noticed while analyzing the ac conductivity by the power law for x = 0. The analysis is satisfactory for 0.15 ≤ x ≤ 0.70 by using Eq.…”

“…The deviation from the Arrhenius law at low temperature has also been reported for LaMnO 3 15,17 and other perovskite material, Sr 0.998 Ca 0.002 TiO 3 . 34 The values of E Ma and τ M0 obtained from the Arrhenius fit are E Ma ≈ 53 meV and τ M0 ≈ 3 ×10 −10 s for x = 0 which are in between the reported values 44 meV and 3.3 × 10 −8 s for polycrystalline, 17 and 86 meV and 3 ×10 −13 s for single crystalline 15 Scaling of the electric modulus can give further information about the dependence of the relaxation dynamics on the temperature, structure and also on the concentration of the charge carriers. Top panel of Fig.…”

“…(5). Since a very small frequency range could be measured for x = 1.0 satisfying pure UDR region the frequency dependence of the 15 In the present investigation temperature dependence of s exhibits similar behavior for different x where s increases approaching toward unity (SU region) with decreasing temperature. The plots in Fig.…”

“…In case of measurement at sufficiently high frequency a cross over from power law, σ ∝ f s to a linear increase of f , σ ∝ f is frequently observed in a variety of materials which is defined as the 'second universality' (SU). 15,25,27,28 The microscopic picture of the origin of SU region at high frequency is still not established. The frequency dependent complex conductivity has been investigated in LaMn 1−x Fe x O 3 for all the compositions.…”

Quantifying the electrical transport characteristics of electron-doped La0.7Ce0.3MnO3 thin films through hopping energies, Mn valence, and carrier localization length

“…Solely sample D does not exhibit an MIT, but a weak plateau at 180 K, which is commonly interpreted as a transition between a paramagnetic-insulating to a ferromagnetic-insulating phase and points towards an insufficient doping [40]. Obviously, the low oxygen partial pressure during the deposition of film D is the origin for the deviating R-T characteristics.…”