Variable-range hopping conductivity and structure of density of localized states in LaMnO₃₊δ under pressure

Abstract

The temperature dependence of the resistivity, ρ, of ceramic LaMnO₃₊δ with δ = 0.065 and 0.154 (or simply # 065 and # 154), is investigated under hydrostatic pressure, p, between the temperatures T = 80 and 320 K in magnetic fields up to 10 T. The data for ρ(T) are analysed within a Shklovskii - Efros-like variable-range hopping conductivity model, governed by a soft Coulomb gap, Δ, and a riidid gap, γ, in the density of localized states. The validity of this approach to the resistivity of LaMnO₃₊δ under ambient pressure was established in recent investigations (Laiho et al 2005 J. Phys: Condens. Matter 17, 105). In the present work it is shown that upon increasing p up to 11 kbar (# 154) and 13 kbar (# 065) the magnetic Curie temperature, Tc, is increased by ~12-13%. Cores ondingly, Δ(p) is decreased by ~ 7-8% and γ(p) by ~ 8% in #154 and 12% in # 065. Similarly, the electron localization radius a(p) is increased by ~ 4% in # 154 and 8% in # 065, respectively. The influence of pressure on Tc, Δ, γ and a is iterpreted by increasing the electron bandwidth and decreasing the polaron potential well, which stimulates the delocalization of electrons when p is increased