Current flow and flux pinning properties of YBCO foam struts
Résumé
The current flow and the flux pinning properties on struts of superconducting YBa2Cu3Ox (YBCO) foams are analyzed in detail in the temperature range 60 K < T < Tc. For this purpose, magnetization loops were measured taken from various positions of a 5 × 2 × 2 cm3 large foam sample prepared at RWTH Aachen. From these data, the critical current densities, jc, and the flux pinning forces, Fp = jc × B, were calculated and pinning force scaling diagrams Fp/Fp,max vs. h = Ha/Hirr were established. The scaling in the temperature range 60 K < T < 90 K was found to be well developed for all samples with peak positions, h0, above 0.4, which is an indication of δTc-pinning. From microstructure analysis of the foam struts employing the electron backscatter diffraction technique (EBSD) [1] it is known that the struts are fully converted into the 123-phase with embedded 211 particles being relatively small. These small 211 particles and their specific distribution within the samples play an important role to explain the observations. The variation of Fp depending on the position of the struts in the original sample directly reveals the changes of the texture as found employing EBSD.
[1] M.R. Koblischka, A. Koblischka-Veneva, E. S. Reddy, G. Schmitz, J. Adv. Ceram. 3, 317 (2014).