Directional solidification of (Re = Y, Nd): microstructure and superconducting properties

Abstract

Single-domain ceramics of ReBa 2 Cu 3 O 7 (Re = Y, Nd) with high T c and high critical currents have been prepared in air by means of directional solidification and the leading microstructural factors controlling the pinning of vortices have been analysed. The interface pinning mechanism at secondary inclusions has been found to be more effective in Y 2 BaCuO 5 than in Nd 4 Ba 2 Cu 2 O 10 in agreement with HRTEM pictures showing sharper interfaces in the first case. The observation of high T c and a vanishingly small fishtail effect in Nd123/422 composites suggest that the concentration of Nd-Ba antisite defects is minimized during the directional solidification process in air. Finally, it is demonstrated by TEM analysis that Nd123/422 ceramics show distinctive microstructural features compared with Y123/211 which could enhance the high-field critical currents and the irreversibility line. Frequency-dependent ac susceptibility studies provide evidence, however, that the thermal activation of vortices is enhanced in Nd123 as compared with Y123. It is suggested that incomplete oxygenation reduces the effective pinning energies.

Mechanical properties of Ag-doped top-seeded melt-grown YBCO pellets

“…Single domain melt-textured YBCO pellets have been prepared by the top seeding technique using melt-textured NdBa 2 Cu 3 O 7−δ seeds [3,4] Room temperature hardness and elastic modulus profiles were determined by instrumented indentation following the Oliver and Pharr method [8]. The diamond tip was a Berkovich type and the applied loads ranged from 2.5 to 320 mN.…”

“…In order to decrease these defect densities and to improve the mechanical properties, it is indicated to dope the high-T C matrix with Ag without loosing the transport properties [2][3][4]. The doped Ag-YBCO structure has Ag inclusions in addition to the Y211 grains in the Y123 matrix.…”

“…The doped Ag-YBCO structure has Ag inclusions in addition to the Y211 grains in the Y123 matrix. These inclusions are formed if the Ag content surpasses the Ag solubility limit in the YBCO structure [3,4].…”

Magnetic irreversibility and zero resistance in melt-textured YBaCuO

“…Our melt-textured sample, containing 30 wt% of Y211 (Y 2 Ba 1 Cu 1 O 5 ) phase and 1 wt% CeO 2 , was prepared by the top-seeding method [5] with a NdBa 2 Cu 3 O 7Àd single crystal on top of the pellet. The measurements were performed on a sample that was a long parallelepiped obtained from a monodomain and having 8 Â 1.3 mm parallel to the abplane and 1.3 mm along the c-axis.…”

Characterization of superconducting rings using an in-field hall probe magnetic mapping system

“…Single domain melt textured YBa Cu O pellets were grown by Top Seeding Growth following processes previously described [1], [3], [6]. A ring shaped sample of YBCO has been obtained by drilling a thin disc.…”