Effect of electron/hole doping on the transport properties of lanthanum manganites LaMnO₃

Abstract

We report the results of electrical resistivity, magnetic susceptibility and thermoelectric power measurements on the stoichiometric hole-doped La(0.8)Ca(0.2)MnO(3) and electron-doped La(0.8)Ce(0.2)MnO(3) manganites. The resistivity and thermopower data show a metal-insulator phase transition for both samples. Magnetic susceptibility measurement confirms that both the samples undergo a transition from paramagnetic to ferromagnetic phase at defined Curie temperatures T(c) = 240 K (La(0.8)Ca(0.2)MnO(3)) and 263 K (La(0.8)Ce(0.2)MnO(3)). The electrical resistivity data are then theoretically analysed within the framework of the classical electron-phonon model of resistivity, i.e. the Bloch-Gruneisen model. Detailed analysis of the electrical resistivity of electron- and hole-doped manganites suggests that besides the electron-phonon effect another possibility for the change in carrier density arises due to the presence of electron correlation in the metallic system. From the thermopower S(T) results, we suggest that its behaviour is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions in the polycrystalline samples of hole-doped La(0.8)Ca(0.2)MnO(3) and electron-doped La(0.8)Ce(0.2)MnO(3) manganites.

Investigation on structural, magneto-transport, magnetic and thermal properties of La0.8Ca0.2−xBaxMnO3 (0⩽x⩽0.2) manganites

“…This behavior is consistent with reports in the literature [34,35]. With Ba doping, the anomaly of transition is monotonically shifting towards higher temperatures and there is an overall decrease in S indicating the samples are becoming more conducting with increase in doping concentration.…”

Structure and electrical resistivity of La1−xBaxMnO3 (0.25≤x≤0.35) perovskites

“…Mixture of stoichiometric amount of La 2 O 3 , BaCO 3 , and MnO 2 was calcined (at 900 • C) in air for 24 h with two intermediate grindings and then sintered (at 1000 • C) for 24 h after being palletized. The pellets were finally annealed at 1000 • C in oxygen atmosphere [23].…”

“…We must mention that the most rapid motion of a small polaron occurs when the carrier hops each time the configuration of vibrating atoms in an adjacent site coincides with that in the occupied site. Henceforth, the charge carrier motion within the adiabatic regime is faster than the lattice vibrations and the resistivity for SPC follows = p T exp(E P /k B T) with the polaron formation energy E p and Boltzman constant k B [23,33].…”

Metallic and semi-conducting resistivity behaviour of La0.7Ca0.3−x K x MnO3 (x = 0.05, 0.1) manganites

“…The estimated electron parameters for La 0.7-Ca 0.25 K 0.05 MnO 3 (La 0.7 Ca 0.2 K 0.1 MnO 3 ) are the Fermi wave vector k F = 3.581 (4.586) 9 10 7 cm -1 , the Fermi velocity v F = 2.035 (2.105) 9 10 7 cms -1 and the plasma frequency x p = 1.406 (1.831) eV. We stress that the effects induced by electron correlations and mass renormalizations by electron-electron interactions are crucial in magnetic systems such as doped manganites [55][56][57][58][59][60][61][62][63][64][65].…”

“…We notice that enhanced electron mass m * = 2.031 (2.514) m e in La 0.7 Ca 0.3-x K x MnO 3 leads to the reduced plasma frequency, and hence the reduced zero temperature elastic scattering rate in comparison to conventional metals. It is perhaps worth noticing that, in holedoped manganites, the scattering rate at low temperatures is of the order of 10 15 s -1 [55][56][57][58][59][60][61][62][63][64][65]. Furthermore, the MottIoffe-Regel criterion for metallic conductivity is valid, as the deduced mean free path is larger than the Mn-O bond length.…”