Variable-range hopping conduction in LaMnO3 + δ

The temperature dependence of the electrical resistivity ρ(T) for ceramic samples of LaMnO3 + δ (δ = 0.100–0.154) are studied in the temperature range T = 15–350 K, in magnetic fields of 0–10 T, and under hydrostatic pressures P of up to 11 kbar. It is shown that, above the ferromagnet-paramagnet transition temperature of LaMnO3 + δ, the dependence ρ(T) of this compound obeys the Shklovskii-Efros variable-range hopping conduction: ρ(T) = ρ0(T)exp[(T0/T)1/2], where ρ0(T) = AT9/2 (A is a constant). The density of localized states g(ɛ) near the Fermi level is found to have a Coulomb gap Δ and a rigid gap γ(T). The Coulomb gap Δ assumes values of 0.43, 0.46, and 0.48 eV, and the rigid gap satisfies the relationship γ(T) ≈ γ(Tv)(T/Tv)1/2, where Tv is the temperature of the onset of variable-range hopping conduction and γ(Tv) = 0.13, 0.16, and 0.17 eV for δ = 0.100, 0.125, and 0.154, respectively. The carrier localization lengths a = 1.7, 1.4, and 1.2 Å are determined for the same values of δ. The effect of hydrostatic pressure on the variable-range hopping conduction in LaMnO3 + δ with δ = 0.154 is analyzed, and the dependences Δ(P) and γv(P) are obtained.