Evaluation of Y-Ba-Cu-O tubes prepared by tape casting and subsequent rate-controlled sintering

Tape-cast samples from commercially available superconducting Y-Ba-Cu-O powder were fabricated. These samples were sintered in oxygen at a constant heating rate within a temperature range of 600-980°C. The information gained was part of the data base used to design a rate-controlled sintering (RCS) schedule which could be employed to achieve clean grain boundaries by preventing peritectic melting. Samples representing different sintering rates (including RCS) were evaluated by X-ray diffraction, SEM, DTA and TGA measurements to derive grain size distribution, oxygen content and chemical composition. Transport and magnetization critical current density (and pinning force density) were calculated from measurements by using the so-called transformer technique and SQUID magnetometer, respectively. AC susceptibility measurements and zero-field cooling and field cooling magnetization measurements were performed to obtain transition temperatures and pinning strength as a function of sintering rates. Tubes of centimeter diameter and millimeter thickness were manufactured by tape casting and RCS for evaluation of typical high-current downleads in cryogenic systems to minimize conduction heat losses to the system.