William John Clegg

Physical and mechanical properties of YBa2Cu3O7-δ superconductors

The physical and mechanical properties of YBa2Cu3O7−° superconductors are examined. These properties are related to powder preparation method, powder characteristics, sintering behaviour and sintered microstructure. The sintering atmosphere and sintering schedules affect the final microstructure very strongly and determine, in conjunction with starting powder characteristics, the sintered density. The mechanical properties such as Youngs modulus, bend strength and critical stress intensity factor (fracture toughness) are measured and related to microstructure as determined by electron microscopy. Control of microstructure by careful powder selection and sintering schedule is seen as key to optimizing the physical and mechanical properties of the material. Finally attention is drawn to fabrication techniques and how these must be optimized in order to realize the mechanical properties which are necessary if these are to be useful as engineering materials. Comparisons between fabrication techniques show that uniaxial powder pressing suffers from limitations in terms of specimen complexity and densification whereas the favoured route, termed viscous processing, gives a more homogeneous microstructure, higher strength and allows near theoretical density to be achieved.

Critical currents of sintered and melt‐textured YBa2Cu3Ox

High critical‐current densities, Jc, have been observed in single crystals and thin films of YBa2Cu3Ox. Jc in bulk materials is diappointingly low reaching a maximum in untextured material of about 103 Au2009cm−2. The importance of raising Jc in bulk materials is paramount and most applications of bulk materials require high Jc in high magnetic fields. The work of Jin et al. in raising Jc to 17u2009000 Au2009cm−2 in zero field represents a most important step in the development of bulk materials and gives real hope to bulk applications. In the communication we first describe the properties of untextured wire, and then we describe our process for melt texturing and the difficulties encountered.

High temperature superconducting ceramics

Abstract We review some of the recent developments in our empirical understanding of the materials science of high T c materials. First, the distinguishing phenomenological Ginzburg-Landau features of these materials are identified, and the possible technological implications discussed. We then focus on two key issues for processing the 1-2-3 materials: oxygen stoichiometry and grain boundary phases. Finally, we briefly examine the impact of the recent discoveries of bismuth-based and thallium-based materials on the field.

Critical currents, magnetisation, AC-susceptibility and AC-losses in ceramic superconductors

Abstract Extensive measurements of critical currents, magnetisation and ac susceptibility have been made on a wide range of YBCO and BiSrCaCuO superconductors. The interrelationship between such measurements and the information they provide on the superconducting properties of high-Tc materials are briefly considered, with particular emphasis on the role of the field-dependent bulk critical current.