Effect of long aging on the resistivity properties of optimally doped YBa2Cu3O7−δ single crystals

•Long time exposure in air leads to the degradation of the conducting properties.•There is emergence of effective scattering centers of the carriers.•In the aging process there are signs of phase separation.

We investigate the conducting properties in the basal ab-plane before and after a long time exposure in air atmosphere of the optimally oxygen doped YBa2Cu3O7−δ single crystals. Prolonged exposure leads to an increase of the effective scattering centers of the normal carriers. The excess conductivity in a wide temperature range has exponential temperature dependence and near the critical temperature is well described within the Aslamazov–Larkin theoretical model. The prolonged exposure increases to a great extent the temperature range of the implementation of the pseudogap state, narrowing the linear section of the temperature dependence of the resistivity in the ab-plane, ρab(Т).