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The effect of medium fluences (from 1019 е/cm2 to 1020 е/cm2) of fast electron irradiation or the change in the praseodymium concentration in the range 0.0 ≤ z ≤ 0.5 on the excess conductivity of optimally oxygen-doped YBa2Cu3O7–δ single crystals has been investigated. Irradiation leads to the appearance of a significant number of defects that cause a decrease in anisotropy, an appreciable increase in phonon scattering, reduction of Tc, and broadening of the superconducting transition. Under the conditions specified, the temperature dependence of electrical resistivity is approximated with high accuracy by the charge carriers' scattering on defects and phonons, and fluctuating conductivity in the Lawrence–Doniach model. It was determined that at fluences 0 ≤ Ф ≤ 6.5⋅1019 е/cm2, the value of the transverse coherence length ξс(0) increases with an increase of Ф by about three times or more than four times as the content of praseodymium in the sample increases to z ≈ 0.42. In both cases, the 2D–3D crossover point shifts upward in temperature. In contrast to the case of irradiation with low fluences (Ф ≤ 1019 е/cm2) or doping with praseodymium up to concentrations z ≤ 0.39, irradiation with medium fluences and doping with praseodymium at higher concentrations leads to a nonmonotonic dependence of the transverse coherence length ξс(0) on the irradiation fluence, with characteristic maxima at Ф ∼ (7–8)⋅1019 е/cm2 or z ≈ 0.42, which may be due to the general suppression of the superconducting characteristics. [ABSTRACT FROM AUTHOR]

In the present work, the effect of all-round compression up to 10 kbar on the in-plane electrical resistivity of well-structured Y0.66Pr0.34Ba2Cu3O7–δ (δ < 0.15, Тс ≈ 51.8 K, ΔТс ≈ 2 K) single crystals has been investigated. In contrast to the samples with low praseodymium doping (x ≈ 0.05), the application of all-round compression to the samples with medium praseodymium doping (х ≈ 0.34) leads to an increase in the baric derivative dТс/dP by more than two times. It was found that, in contrast to polycrystalline samples, there was no change in the sign of the baric derivatives dТс/dP. The applicability of the well-known McMillan formula to explain the effect of all-round compression on Тс is discussed. [ABSTRACT FROM AUTHOR]

The effect of medium doses (from 1019 to 1020 cm–2) of irradiation with fast electrons (energy, E = 2.5 MeV) on the excess conductivity of optimally doped Y1Ba2Cu3O7–δ single crystals has been studied. It is shown that the irradiation with electrons leads to the significant expansion of the temperature interval for the existence of excess conductivity, thereby narrowing the region of the ρ(T) linear dependence in the ab plane in the normal state. It has been established that at doses of 0 ≤ D ≤ 6.5⋅1019 cm–2, the value of the transverse coherence length ξc(0) increases with D by about 3 times and the 2D–3D crossover point shifts in temperature. In contrast to the case of irradiation with low doses (D ≤ 1019 cm–2), irradiation with medium doses leads to a nonmonotonic dependence of the transverse coherence length ξc(0) on the irradiation dose, with a characteristic maximum at D ∼ (7–8)⋅1019 cm–2, which may be related to the general suppression of superconducting characteristics. [ABSTRACT FROM AUTHOR]

The anisotropy of the conduction mechanisms of Y1−yPryBa2Cu3O7−δ single crystals has been studied in a wide range of praseodymium concentrations in the region of the transition from metallic to semiconductor conductivity with account fluctuation conductivity in the 3D Aslamazov–Larkin model. The correspondence of the obtained experimental results with the predictions of various theoretical models is analyzed. The anisotropy of Tc increases with increasing y, and the anisotropy of Tc increases most sharply when approaching the nonsuperconducting composition. As the concentration of praseodymium increases, the anisotropy of the ideal resistance passes through a maximum at y ≈ 0.19. It is shown that the temperature dependence of the anisotropy of the resistance in the semiconductor state exhibits a maximum associated with jumps of variable length along the c axis. At the same time, the temperature dependence of the fluctuating conductivity anisotropy passes through a maximum due to the significant anisotropy of the coherence length. [ABSTRACT FROM AUTHOR]

Here, we study the impact of high hydrostatic pressure (up to 11 kbar) on the conductivity in the basal ab plane of Y0.77Pr0.23Ba2Cu3O7–δ single crystals. Conversely to YBa2Cu3O7–δ single crystals, it was found that high pressure leads to phase separation in the basal plane of Y0.77Pr0.23Ba2Cu3O7–δ single crystals. The mechanisms of the influence of praseodymium and high hydrostatic pressure on the two-step resistive transition to the superconducting state are discussed. [ABSTRACT FROM AUTHOR]

The aim was to conduct comparative studies of the evolution of conductivity along and across the base ab plane in Y 1 − z P r z B a 2 C u 3 O 7 − δ single crystals at different degrees of praseodymium doping in a wide range of concentrations 0 ≤ z ≤ 0.5. It is established that the increase in the degree of praseodymium doping in samples Y 1 − z P r z B a 2 C u 3 O 7 − δ leads to increased effects of localization and implementation in the system of metal–insulator type transition, which always precedes the superconducting transition. Increasing the concentration of praseodymium leads to a significant shift in the beginning of the metal–insulator transition at the low temperature region. [ABSTRACT FROM AUTHOR]

The aim was to conduct comparative studies of the evolution of conductivity along and across the base ab plane in Y 1 − z P r z B a 2 C u 3 O 7 − δ single crystals at different degrees of praseodymium doping in a wide range of concentrations 0 ≤ z ≤ 0.5. It is established that the increase in the degree of praseodymium doping in samples Y 1 − z P r z B a 2 C u 3 O 7 − δ leads to increased effects of localization and implementation in the system of metal–insulator type transition, which always precedes the superconducting transition. Increasing the concentration of praseodymium leads to a significant shift in the beginning of the metal–insulator transition at the low temperature region. [ABSTRACT FROM AUTHOR]

In the present work, we investigated the influence of high hydrostatic pressure up to 11 kbar on the conductivity in the basal ab-plane of medium-doped with praseodymium (x≈0.23) single-crystal Y1-xPrxBa2Cu3O7-δ samples. It was determined that, in contrast to the pure YBa2Cu3O7-δsamples with the optimal oxygen content, the application of high pressure leads to the formation of phase separation in the basal plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals. Possible mechanisms of the effect of Pr doping and high pressure on the two-step resistive transition to the superconducting state are discussed. It was determined that in the normal state, the conductivity is metallic and is limited by phonons scattering (Bloch-Grüneisen regime) and defects. The fluctuation conductivity is considered within the Lorentz-Doniach model. Hydrostatic pressure, accompanied by a decrease in anisotropy, leads to a decrease in the residual and phonon resistances. Debye temperature and coherence length are independent of pressure. The applicability of the McMillan formula in the presence of significant anisotropy is discussed. [ABSTRACT FROM AUTHOR]