The manufacture of high temperature superconducting tapes and films

An investigation has been carried out on aspects of the manufacture of high temperature superconducting films. Initially, a study was made of tapes manufactured, from the recently discovered thallium-based superconducting material, (Tl0.6Pb0.2Bi0.2)(Sr1.8Ba0.2)Ca2Cu3O9+δ, via a powder-in-tube technique. Particular attention was paid to the microstructural evolution of the tapes' core with temperature. It was found that the platelet-like as-prepared powder formed superconducting tapes that displayed partial texturing, a feature not before observed in thallium-based tapes of this kind. The synthesised powder had an excellent intra-grain critical current density of 6.5 x 104 A cm-2 in an applied magnetic field of 1 T, at 77 K, with a superconducting transition temperature, TC, of 110 K. Moreover, the powder was relatively simple to prepare, normally a problem inherent in 'shake and bake' preparation of thallium materials. Transport critical current densities up to 5.6 x 103 A cm -2 in a field of 0 T, at 77 K, were measured in short lengths of tape. The problem of weak grain connectivity was confirmed.The difficulties pertaining to the manufacture of long lengths of superconductor by the application of the powder-in-tube approach guided the research toward an area where continuous processing had already been established - electrodeposition. A detailed study of the electrochemical fabrication of superconducting precursor films was performed. Fundamental measurement of the metals involved was carried out and then a range of precursor films synthesised and analysed in order to understand the electrodeposition process of multi-metal co-deposition. Major control parameters involved in the process, affecting both intrinsic film characteristics and reproducibility, were temperature, applied potential, deposition technique, and solution composition. A procedure was developed that yielded a highly reproducible process with quality films exhibiting void percentages from as low as 45% up to 90%. Heat treatment of selected films resulted in high purity, highly aligned Bi2Sr2CaCu2O8-δ films with TC's � 98 K, and multi-phase (Tl, Pb)Sr2Ca2Cu3O9-δ films with TC's � 115 K, and magnetic critical current densities of 4.99x 105 A cm-2, and 1.26 x 106 A cm-2 at 77 K, 1 T, respectively.