Predicted Mechanical Behavior of High-T c Superconducting Ceramic Films

Abstract

In potential applications, the recently discovered high transition temperature (high-Tc) ceramic superconductors (Bednorz and Muller, 1986, Wu et al., 1987, Cava et al., 1987) may experience large mechanical stresses and strains. These can be imposed by magnet fabrication, high magnetic fields, and, in the case of superconducting films, also by thermal contraction mismatch with the substrate material (see, for instance, Baynham, 1988, Severin and de With, 1988). Although mechanical strength of a superconductor may appear to be not as important a property, as, say, high superconducting transition temperature, high upper critical magnetic field or high critical current density, it may play a decisive role, when a superconducting material is used for practical purposes. Since ceramics are brittle materials, and break quite easily when stretched, bent or hit, use of ceramics as practical superconductors requires that they possess high ultimate stress and strain, sufficient fracture toughness and good shock resistance. It is also important that the actual stresses and strains arising in superconducting ceramics at low temperatures can be predicted and, if possible, minimized.