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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]

Measured is the transverse electrical resistance of YBa 2 Cu 3 O 7− δ single crystals with different oxygen deficiency values ( δ ) in the temperature range T c − 300 K. The experimental data are approximated by an empiric expression accounting for the fluctuation conductivity near T c and the semiconductor-like resistance regime. Our analysis of the concentration dependences of the fitting parameters, in particular, reveals that the resistance temperature dependence is largely affected by the sample's non-homogeneity. The latter, in turn, causes a T c anisotropy and variable-range hopping conductivity between different phases. The deduced maximal values of the basal-plane coherence length, ξ xy (0), are comparable with those for low-temperature superconductors. [ABSTRACT FROM AUTHOR]

Abstract: 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, ρ ab(Т). [Copyright &y& Elsevier]

Abstract: In the present work the effect of hydrostatic pressure up to 10kbar on in-plane electrical resistivity of well-structured YBa2Cu3O7−δ (δ<0.15, Т с≈91K, ΔТ с≈0.3K) single crystals was investigated. The influence of the twin boundaries on the electrical resistivity was minimized. The resistivities temperature dependences in the interval Т с up to 300K can be approximated by taking into account the linear term at high temperatures and the fluctuation conductivity (Maki–Thompson model) near Т с. The parameters of the linear dependence of R(T) are decreasing as the pressure is increasing. Т с increases linearly when the pressure increases with the derivative dT c /dP≈0.080K/kbar. Among the Maki–Thompson model parameters the inter-layer distance, d, can be considered to be independent from pressure, the transverse coherence length, ξ c (0)∼0.1d. [Copyright &y& Elsevier]

Abstract: We investigate the relaxation of the normal electrical resistivity, induced by high-pressure in YBa2Cu3O6.45 single crystals. It is determined that the pressure affects to the phase composition of the sample. Under pressure phases with different (but similar) critical temperatures form. It is determined that the application-removal pressure process is completely reversible. Above T c the temperature dependence of the resistivity in the layers'' plane at different hydrostatic pressures can be approximated with high accuracy with the scattering of electrons by phonons model. With increasing pressure, the residual resistance is reduced and the contribution of intraband s–s scattering increases. Additionally, the role of the interband s–d scattering and the Debye temperature is enhanced. [Copyright &y& Elsevier]

The effect of hydrostatic pressure up to 12 kbar on electrical resistance in the basal ab-plane of optimally oxygen-doped Y 1– x Pr x Ba 2 Cu 3 O 7–δ single crystals doped with praseodymium (х ≈0.23) has been investigated. It was determined that the introduction of praseodymium leads to a fivefold increase in the baric derivative dT c / dP at zero pressure; however, as the pressure rises, dT c / dP decreases to a level characteristic of undoped Y 1– x Pr x Ba 2 Cu 3 O 7–δ samples with an optimal oxygen content. • hydrostatic pressure does not affect the morphology of a superconducting cluster in Y 1- x Pr x Ba 2 Cu 3 O 7-δ. • Pr leads to a fivefold increase in the baric derivative dT c / dP at zero pressure. • As pressure rises, dT c / dP decreases to a level characteristic of undoped Y 1– x Pr x Ba 2 Cu 3 O 7–δ. [ABSTRACT FROM AUTHOR]