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In the present study, the time dependencies of the resistivity of ReBa 2 Cu 3 O 7 − x (Re=Y, Ho) single crystals with varying degree of deviation from oxygen stoichiometry was investigated. It was shown that the accelerated transport of oxygen ions in the initial stage of the process can be carried out along the one-dimensional non-stoichiometric vacancies’ accumulation by the single file diffusion mechanism. The final phase redistribution of oxygen ions in ReBa 2 Cu 3 O 7 − x (Re = Y, Ho) is described by the classical mechanism of volume diffusion. The substitution of yttrium by holmium significantly affects the charge redistribution and changes the efficient interaction of ions in CuO-planes, thereby modifying the mass transfer diffusion mechanisms in the oxygen sublattice. Thus, a significant length change of the time intervals occurs, corresponding to the oxygen ions’ single file and volume diffusion mechanisms. [ABSTRACT FROM AUTHOR]

The effect of external hydrostatic pressure on the electrical resistance of optimally doped and underdoped YBa 2 Cu 3 O 7 - δ single crystals is investigated in a broad temperature range, which includes the normal state and the region of superconducting fluctuations. The temperature dependences of the resistivity in the normal state are determined by scattering of charge carriers by phonons and defects. The application of pressure leads to significant changes in the electronic structure of the sample and reduces the degree of their defectiveness. This is accompanied by changeû in the lattice characteristics as the sample volume decreases. The fluctuation conductivity only exists within the range of ∼ 0.1 T c . With increasing δ the superconducting characteristics are close to the values typical for conventional low-temperature superconductors. [ABSTRACT FROM AUTHOR]

The effect of high hydrostatic pressure up to 17 kbar on the fluctuation conductivity of lightly Pr-doped Y 1− x Pr x Ba 2 Cu 3 O 7− δ ( x ≈ 0.05) single crystals is investigated. We show that in contrast to non-doped YBa 2 Cu 3 O 7− δ samples, application of a high pressure leads to a substantial increase of the pressure derivative of the coherence length dξ c / dP and a temperature shift of the 2D-3D crossover point. Possible mechanisms of the influence of high pressure on the critical temperature and the coherence length are discussed within the framework of a model assuming the presence of singularities in the charge carriers electron spectrum typical for lattices with strong coupling. [ABSTRACT FROM AUTHOR]

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]