Quasi one-dimensional hopping conductivity of the non-stoichiometric spin-ladder CaCu2O3 single crystal

Resistivity, ρ (T), of the spin-ladder compound CaCu2O3 is investigated between T ∼ 100 - 350 K. Both nearest-neighbor hopping, ρ (T) ∼ exp (Ea/kT), and variable-range hopping, ρ (T) ∼ exp [(T0/T)3/4], quasi one-dimensional conductivity mechanisms are observed above and below T ∼ 200 K, respectively. The activation energy Ea and the VRH characteristic temperature T0 exhibit high sensitivity to the cation (Ca, Cu) content, attributable to a corresponding variation of the concentration of intrinsic defects associated with Cu vacancies. On the other hand, no direct dependence of Ea and T0 on the excess oxygen concentration is found. (authors)