Fracture toughness of REBaCuO bulk superconductor at liquid nitrogen temperature

The fracture toughness of Y123 and Gd123(Ag) single-grain bulk samples with 25 mol% RE 211 phase (and 10 wt.% Ag for the latter) prepared by the modified quench and melt-growth technique, was evaluated by the 3-point bending test at liquid nitrogen temperature (LNT) and room temperature (RT). The sharp V-notch was introduced into the specimens such that both of the loading and the crack extension directions are in the c-axis. The data for Y123 scattered from 1.2 to 2.0 MPam(1/2) at LNT and 1.4 to 1.7 MPam(1/2) at RT. The average value at LNT, 1.6 MPam(1/2), was slightly higher than that for RT, 1.5 MPam(1/2). For Gd123(Ag) the average fracture toughness at LNT, 1.8 MPam(1/2) was higher than that at RT. The temperature dependence of fracture toughness for two kinds of bulks was consistent with that of the bending strength. Further, the order of the magnitude of the fracture toughness almost corresponded with that of bending strength for both bulks. (c) 2005 Elsevier B.V. All rights reserved.