Small polaron hopping in spinel manganates

Abstract

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In-plane impedance spectroscopy in aerosol deposited NiMn2O4 negative temperature coefficient thermistor films

“…The p and g(0.15 eV) values of the annealed films are in good agreement with bulk NiMn 2 O 4 values reported previously. 36 In contrast, the as-deposited films show a lower density of localized electron states contributing to the hopping process. Obviously, annealing and concomitantly improved film crystallization bring the charge transport properties of AD films closer to the bulk behavior.…”

“…A temperature dependent activation energy for electron hopping was found many decades ago, 1 but only more recently has a theoretically justified small polaron variable-range hopping (VRH) model been employed more frequently. [32][33][34][35][36] In this work, we present a detailed in-plane impedance spectroscopy (IS) study on approximately 2 lm thick NMO films produced via the aerosol deposition (AD) technique using glass and Al 2 O 3 substrates. 28 The recently developed AD technique offers several distinct advantages: it allows highly dense polycrystalline films of sub-micrometer grain size to be produced with a high deposition rate and without an additional sintering densification process.…”

Dielectric response to the low-temperature magnetic defect structure and spin state transition in polycrystallineLaCoO3

“…͑5a͒ and ͑5b͔͒. 43,44 By using an estimated value for the localization length a =1/ ␣ of electrons participating to the hopping transport, for example, from the cationic radius of 0.6 Å for Co 3+ ͑based on an ionic model neglecting the covalent character of the bonds͒, 45 the DES near Fermi level N͑ F ͒ and r max at 50 K were calculated according to expressions ͑5a͒ and ͑5b͒. 43,44 The values are shown in Table I,…”

Magnetoimpedance spectroscopy of epitaxial multiferroic thin films

“…Although only few data points are available here to suggest VRH charge transport to occur, possibly between defect Mn 2+ and Mn 3+ cations, it should be noted that the T dependence of charge transport in mixed valence manganitehopping systems commonly follows VRH laws. 59,60 A linear least-squares routine was employed to fit the Arrhenius ln(ρ 1 ) vs 1/T curve to Eq. (2) for T T C .…”