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We reveal that the temperature dependence of the basal-plane normal-state electrical resistance of optimally doped YBa 2 Cu 3 O 7 − δ single crystals can be with great accuracy approximated within the framework of the model of s-d electron-phonon scattering. This requires taking into account the fluctuation conductivity whose contribution exponentially increases with decreasing temperature and decreases with an increase of oxygen deficiency. Room-temperature annealing improves the sample and, thus, increases the superconducting transition temperature. The temperature of the 2D-3D crossover decreases during annealing. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the influence of the disorientation angle between the direction of a constant magnetic field (up to 15kOe) and the ab-plane α ≡∠(H,ab) to the temperature dependence of the excess conductivity in the temperature interval of the transition to the superconducting state in untwinned YBa2Cu3O7−δ single crystals. We discuss the appearance of low temperature “tails” (para-coherent transitions) on the resistive transitions, corresponding to different phase regimes of the vortex-matter state. At temperatures above the critical temperature, the temperature dependence of the excess para-conductivity is interpreted within the Hikami–Larkin theoretical model of the fluctuation conductivity for layered superconductors. [Copyright &y& Elsevier]

Abstract: Perovskites and related oxides are a very important class of functional materials that exhibit a range of stoichiometries and crystal structures. The oxygen diffusion mechanisms and activation energies in these materials are highly influenced by the composition, stoichiometry and crystal structure. We review the significance of a range perovskite related oxides but focus on two characteristic materials: La2NiO4+δ and LnBa2Cu3O7−δ (where Ln =rare-earth cations). La2NiO4+δ is considered as a cathode material for solid-oxide fuel cells, whereas LnBa2Cu3O7−δ is the archetypal superconducting oxides. [Copyright &y& Elsevier]

Abstract: 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 20K. 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. [Copyright &y& Elsevier]

Investigates the effect of low-temperature annealing on the superconducting transition temperature and electrical resistance of single crystals of YBa(sub 2)Cu(sub 3)O(sub 7-sigma) quenched from temperatures of 620-650 degrees Celsius. Increase in transition temperature and decrease in resistance during annealing; Isothermal relaxation of resistance.

Abstract: We investigate the influence of praseodymium content on the basis plane conductivity of Y1− х Pr х Ba2Cu3O7− δ single crystals. An increase of the praseodymium concentration leads to the enhancement of the localization effects and the appearance of a metal–insulator transition in the system, which always precedes the superconducting transition. The increase of the concentration of praseodymium, leads to a significant displacement of the point of the metal–insulator transition in the low temperature region. [Copyright &y& Elsevier]