Structural relaxation, metal-to-insulator transition and pseudo-gap in oxygen deficient НоBa2Cu3O7−δ single crystals

The effect of annealing at room temperatures on the conductivity in the basis plane of oxygen deficient HoВа2Сu3О7−δ single crystals, tempered from a temperature of 650 °C is investigated. We determine that during the annealing process an extension of the area of the linear dependence of the resistivity ρab(T) occurs. A shift downwards of the temperature interval corresponding to the metal-to-insulator transition and a considerable transformation of the form of the resistivity transfers to the superconducting state was observed. The absolute value of the temperature that the pseudo-gap regime commences is reduced by about 20 K. The results are attributed to labile oxygen ordering without changing the concentration of oxygen in the sample. The estimation of the cluster sizes is characterized by the differences in oxygen content. We perform a comparative analysis between the experimental data with the predictions of the high temperature superconductivity cluster theory.