title: Lattice distortions, magnetoresistance and hopping conductivity in LaMnO(3+δ).
abstract: Structural and transport properties of ceramic LaMnO(3+δ) are investigated for δ = 0-0.154. According to x-ray diffraction measurements at room temperature the crystal structure of this compound varies from orthorhombic (Pbnm) for δ = 0 to rhombohedrally distorted cubic (Pm3m) for δ = 0.065-0.112 and to rhombohedral ([Formula: see text]) crystal symmetry for δ = 0.125-0.154. These structural modifications are confirmed by the Raman micro-spectroscopy measurements. The resistivity displays in the range δ = 0-0.154 an activated behaviour both above and below the paramagnetic (PM) to ferromagnetic transition temperature, T(C). In the field of 8 T the relative magnetoresistance, Δρ(B)/ρ(0), reaches at δ = 0.154 the values of -88% near T(C) and -98% at [Formula: see text] K. The resistivity of the PM phase of LaMnO(3+δ) with δ = 0.100-0.154 satisfies the Shklovskii-Efros-like variable-range hopping (VRH) conductivity law between [Formula: see text] K and the VRH onset temperature [Formula: see text] K. The resistivity is governed by a complex energy dependence of the density of the localized states near the Fermi level, comprising a soft Coulomb gap [Formula: see text] eV and a rigid gap [Formula: see text] eV, the latter being connected to formation of small polarons.
authors.affiliation: Wihuri Physical Laboratory, University of Turku, FIN-20014 Turku, Finland.
authors.forename: R
authors.initials: R
authors.lastname: Laiho
authors.forename: K G
authors.initials: KG
authors.lastname: Lisunov
authors.forename: E
authors.initials: E
authors.lastname: Lähderanta
authors.forename: V S
authors.initials: VS
authors.lastname: Stamov
authors.forename: V S
authors.initials: VS
authors.lastname: Zakhvalinskii
authors.forename: Ph
authors.initials: P
authors.lastname: Colomban
authors.forename: P A
authors.initials: PA
authors.lastname: Petrenko
authors.forename: Yu P
authors.initials: YP
authors.lastname: Stepanov