The resistivity, ρ, of ceramic La1−xCaxMn1−yFeyO3 with x = 0.3 and y = 0.0–0.09 is found to obey, between a temperature Tv ≈ 310–330 K and the ferromagnetic-to-paramagnetic transition temperature, TC = 259–119 K (decreasing with y), the Shklovskii–Efros-type variable-range hopping conductivity law, ρ(T) = ρ0 (T) exp [(T0 /T)1/2 ]. This behaviour is governed by generation of a soft Coulomb gap Δ ≈ 0.42 eV in the density of localized states and a rigid gap δ(T) ≈ δ(Tv)(T/Tv)1/2 with δ(Tv) ≈ 0.16, 0.13 and 0.12 eV at y = 0.03, 0.07 and 0.09, respectively. Deviations from the square root dependence of δ(T), decreasing when y is increased, are observed as T → TC. The prefactor of the resistivity follows the law ρ0 (T) ∼ Tm, where m changes from 9/2 at y = 0 to 5/2 in the investigated samples with y = 0.03, 0.07 and 0.09, which is connected to introduction of an additional fluctuating short-range potential by doping with Fe.

Mechanisms of the resistivity, ρ, of single crystal samples oriented along the [100] (No 1), [010] (No 2) and [001] (No 3) axes of anisotropic semiconductor p-CdSb doped with 2 at.% of Ni are investigated. In zero magnetic field the Mott type variable-range hopping (VRH) conductivity is observed in No 2 and the Shklovskii–Efros type in No 1 and No 3 at T≤2.5 K. The magnetoresistance (MR) of the samples obeys the law lnρ∼B2 up to B∼6 T. However, the temperature dependence of MR gives evidence for the Mott-VRH conductivity in No 1 at T≤4.2 K and the nearest-neighbor hopping conductivity in No 2 between T = 3 and 4.2 K and in No 3 between 1.5 and 4.2 K. From the experimental data the values of the localization radius and dielectric permittivity and details of their critical behavior near the metal–insulator transition, as well as the widths and the values of the density of the localized states, the acceptor energies, their concentrations and the anisotropy coefficients, are obtained.

Low-field magnetic properties of ceramic La1-xCaxMnO3 (0⩽x⩽0.4) are investigated between T = 5 and 310 K. The paramagnetic-ferromagnetic transition is observed in all the samples. The dependence of the Curie temperature, TC, on x is described within a model of spin polarons associated with electronic localization. Critical behaviour of the susceptibility χ-1(T ) ~ (T-TC)γ is observed for T>TC, with the critical exponents γ = 1.20±0.05 and γ* = 1.64±0.06 below and above the composition x≈0.18 corresponding to the Mn4+ ion concentration c ≈ 0.23, respectively. For the compound with x = 0.3 no temperature hysteresis of the resistivity is observed in magnetic fields between 0 and 8 T. In all the samples the field-cooled and zero-field-cooled magnetizations deviate below TC, the difference being approximately equal to the thermoremanent magnetization (TRM). Long-time relaxation of TRM in LCMO is observed for time scales up to 104 s. The relaxation rate reaches a maximum near a wait time tW ~ 103 s. The time dependence of TRM can be described with a stretched exponential law, as in spin or cluster glasses in conditions where the observation time is comparable with tW .

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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.