Microstructure and critical current of superconducting YBa2Cu3O7−x

Practical significance of the ferroelastic nature of the superconductor Y-Ba-Cu-O

“…Cannelli et aL31 carried out anelastic relaxation measurements of flexural vibration modes (in the kHz range), and obtained from their data the following expression for the diffusion coefficient of the basal-plane oxygens in oxygen-deficient YBCO: D = 4 x lop4 exp (-0.11 eV/kT) cm2/sec. (20) This indicates very high diffusivity; for T = 300 K, it corresponds to D = 6 x cm2/sec, very similar to the value for hydrogen atoms in Nb.31 Clearly, an extremely small driving stress is sufficient to induce oxygen-hopping and the attendant ferroelastic switching across (110) walls.…”

High Tc ceramic superconductors: Introduction, background, and challenges to the electron microscopist

“…Although high T, ceramics with sharp transition temperatures in the region of 90°K can now be routinely synthesized, the production of materials with high critical current densities is still problematical. Transport measurements on single crystals and oriented films have demonstrated that the intrinsic transport critical current density is high (J, = lo6 A.cm2; see Camps et al, 1987, andChaudari et al, 1987). However, polycrystalline ceramics have yet to reach the same levels ("good" materials have J, .…”

“…The diffusion coefficients for oxygen transport in the bulk material are high (Farrington, Davies and Rohrer, University of Pennsylvania, unpublished work); however, in dense ceramics the oxidation of the samples can perhaps be severely limited by non-ionically conducting grain boundary phases. The structure of the grain boundaries has recently received some attention, in particular two recent EM papers have investigated the structure of grain boundaries in samples with varying grain sizes and current densities (Camps et al, 1987Nakahara et al, 1988. In the future these areas might be expected to receive more attention.…”

External and Internal Diffusion of Oxygen in Superconducting YBa2Cu3O7−x Composite Conductors

“…At present the primary problem is the control of the critical current density, Jc" which is still some two to three orders of magnitude smaller than that of conventional metallic superconductors [1][2][3][4]. Although such low values make it unlikely that commercial wires will be produced in the short term we consider it important to explore different concepts in wire design and the effect of fabrication variables on conductor properties.…”