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

Abstract

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.