EVOLUTION OF THE TEMPERATURE DEPENDENCES OF ELECTRICAL RESISTANCE OF Y1-XPrXBa2Cu3O7-δ SINGLE CRYSTALS IN A WIDE RANGE OF APPLIED PRESSURE AND CONCENTRATIONS OF PRASEODIUM IMPURITIES

Abstract

The effect of high hydrostatic pressure 0 ≤ Р ≤ 17 kbar on the electrical resistance ρ(Т) in the basic ab-plane of praseodymium-doped single crystals of the Y_1–xPr_xBa₂Cu₃O_7–δ system at 0 ≤ х ≤ 0.34 was investigated in the paper. Single crystals of compounds       Y_1–xPr_xBa₂Cu₃O_7–δ were grown by solution-melt technology in a gold crucible. Hydrostatic pressure was created in a piston-cylinder multiplier. The pressure was determined with a manganin manometer, and the temperature – with a copper-constantane thermocouple.

It was established that an increase in pressure leads to an increase in the critical temperature of the studied compounds and a decrease in their electrical resistance, which corresponds to literature data for polycrystalline samples. Near the superconducting transition, the appearance of the temperature derivatives of the electrical resistance, dr/dT, of the Y_1–xPr_xBa₂Cu₃O_7–δ compounds indicates a certain heterogeneity of the samples, i.e., the presence of areas in the samples with different temperatures of the superconducting transition, T_с, which transition to the superconducting state as T_с is reached. At intermediate concentrations of praseodymium, such regions pass into the superconducting state sequentially, but at x = 0 and x = 0.34, the form dr/dT indicates the presence of percolation paths for the flow of the transport current. The value of T_c and literature data on the Debye temperature indicate that the McMillan formula can be applied only to compounds Y_1–xPr_xBa₂Cu₃O_7–δ that have T_c < 65 K (that is, for x, d > 0.3), and at the same time gives a very high values of the electron-phonon interaction constant, l ~ 1. It was found that, in contrast to pure YBa₂Cu₃O_7–δ samples with optimal oxygen content, the application of high pressure leads to a multiple increase in the value of the baric derivative dT_c/dP. It was established that within the limits of experimentally achieved pressures, there was no change in the sign of baric derivatives dT_c/dP with increasing pressure, which was observed on polycrystalline samples with close values of praseodymium concentration. The possible mechanisms of the effect of high pressure on the critical temperature of the transition to the superconducting state T_c are discussed, taking into account the features in the electronic spectrum of carriers.