9402117 Eddy, Michael The preparation of epitaxial TlBaCaCuO (TBCCO) and YBa2Cu3O7-8 (YBCO) films has been demonstrated on a small number of substrates. At present, LaAlO3 is inert, minimizing interdiffusion between the substrate and superconductor and has a good lattice match to the HTS structure. However, there are limitations to its wide-scale use. The two most significant problems are the high dielectric constant (23.5) and twinning. The most promising near-term alternative substrate which does not have these problems is MgO; however, growth of high quality TBCCO films on this substrate is difficult. In addition, for YBCO, the quality of the superconductor is degraded relative to YBCO on LaAlO3. MgO will be used as the substrate in Phase II because of the thermal expansion match between MgO and the superconductor.
