Adiabatic and non-adiabatic small-polaron hopping conduction in La_1−xPb_xMnO_3+δ(0.0 ≤x≤ 0.5)-type oxides above the metal–semiconductor transition

Abstract

Above the semiconductor-to-metallic transition (SMT) temperature (Tp), transport properties of the La1−xPbxMnO3+δ (0 ≤ x ≤ 0.5)-type mixed valence oxides with Tp between 230 and 275 K (depending on x) have been thoroughly examined for a small-polaron hopping conduction mechanism of the carriers. Although the variable range hopping (VRH) model was used earlier to fit the entire conductivity data above SMT, we noticed two distinct regions (above and below θD/2; θD is the Debye temperature) where different types of conduction mechanisms are followed. The high temperature (T > θD/2) conductivity data of all the Pb-doped samples follow the adiabatic hopping conduction mechanism, while those of LaMnO3 (x = 0) showing no SMT follow the non-adiabatic hopping conduction mechanism of Mott or Emin with reasonable values of polaron radius, hopping distance, polaron binding energy, activation energy, etc being different for different systems. The VRH model, however, fits the corresponding low temperature (T < θD/2) data of all the samples. Both resistivity ρ(T) and thermoelectric power S(T) follow a similar microscopic theory above Tp supporting the small-polaron hopping mechanism. Thermoelectric power also showed appreciable magnetic field dependence around SMT.

Synthesis and electric characterization of rare earth double perovskite Ho2CdZrO6 ceramics

“…(8). This value of location length L is found to be in the same order of magnitude as reported by Mahato et al [6,24] for double perovskite oxides. The average hopping distance, R h (T) between two localized states and hopping energy, E h (T), are given by the following equations [22]:…”

“…7. The reported value of N(E F )(05.68×10 17 eV -1 cm -3 ) [21,22,24,25] yields a location length L of the order of 18 Å for HCZ as calculated from Eq. (8).…”

“…Such a curvature in the plot suggested that the variable range hopping (VRH) of small polaron model could be concerned in such a case. The variable range hopping of small polaron conductivity model described the conductivity with the formula [21][22][23][24][25]:…”

Conducting mechanism in the epitaxialp-type transparent conducting oxideCr2O3:Mg

“…SPH typically occurs in mixed-valence transition metal oxides where the electron-lattice interaction is strong [39,54,55]. Unlike in the free electron model, charge is localized to the lattice, or polarized.…”

Influence of ion implantation on the magnetic and transport properties of manganite films

“…The VRH conductivity for 3D systems is given by where T 0 is the distance between conducting zones in a 4D space, formed given by the real space distance and the difference of energy. VRH has been observed in cation substituted manganites [34], in substrate-induced disordered films [9] and for La 1-x Pb x MnO 3 polycrystalline samples with x = 0.1 and 0.5 [35]. The inset of figure 8 shows the exponential dependence of T 0 with increasing point defect disorder.…”