Single Crystals Of high-Tc Superconductors Research Articles

Grain Boundary Doping May Improve High-Temperature Superconducting Wire

Superconducting wire is a central part of many of the applications devised for high-temperature superconductors in the 15 years following their discovery. With transition temperatures Tc above the boiling temperature of liquid nitrogen (77 K), these superconductors have the potential to provide cheap, low-loss wires capable of carrying large currents. The technological realization of this potential has been difficult, however, due in part to the anisotropic character of the ceramic high-Tc materials. Although single crystals of high-Tc superconductors have high critical current densities—the figure of merit in wire applications—polycrystalline wires suffer from significantly reduced current-carrying ability.

“Fishtail” in a magnetic hysteresis loop of an anisotropic superconducting disk

The critical state equations for an anisotropic superconducting disk are represented in the easy-to-use form. With the use of these equations the new explanation for the “fishtail” effect in magnetic hysteresis loops of single crystals of high-T c superconductors is offered.

Thermally activated flux avalanches in single crystals of high-Tc superconductors.

We have experimentally investigated long-time ([gt]10 h) magnetic relaxation in single crystals of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub [ital x]] and YBa[sub 2]Cu[sub 8]O[sub [ital x]] at wide ranges of temperature and field. We have found that the flux motion in single crystals of high-[ital T][sub [ital c]] superconductors exhibits two distinctly different behaviors at a wide regime of driving force. At large driving force, the flux motion is dominated by thermally activated avalanches, which can be described by a so-called self-organized criticality theory. At small driving force, however, the avalanche effect is significantly reduced, and the flux motion is characterized by slow creep which can be described by the Anderson-Kim model. Therefore, there is a dynamic crossover between the flux avalanches and a pure thermally activated regime in high-[ital T][sub [ital c]] superconductors.

Modulation technique for measuring critical current density in single crystals of high-Tc superconductors

Abstract A contactless AC modulation method for determining critical current density in a strong magnetic field is described. By using this technique critical-current measurements in magnetic fields up to 90 kOe were performed on a Dy 1 Ba 2 Cu 3 O 7− δ single crystal at different orientations of the specimen with respect to the magnetic field.

Growth and annealing effect of single crystals of high-Tc superconductors

Detailed informations on the crystal preparations of (La1−xSrx)2CuO4−δand YBa2Cu3O7−δ are reported. The Sr content x in (La1−xSrx)2CuO4−δ crystals is shown as a function of the Sr content in the initial mixtures. For YBa2Cu3O7−δ, the conditions to get three types of crystals, thin plate, rectangular cube and irregular block shapes are described. Annealing effect on the resistivities of these crystals is also reported.