IMPORTANCE OF THERMODYNAMICS AND KINETICS IN THE GROWTH OF THIN-FILM TLBACACUO SUPERCONDUCTORS

The importance of near-equilibrium thermodynamics in the growth of TlB aCaCuO materials is well-documented; i.e, the independent control of s ample temperature, Tl-oxide partial pressure, and oxygen partial press ure. Here we demonstrate how this is accomplished using a simple versi on of the crucible process. In addition, we report the relevance of gr owth kinetics. Superconducting thin films are grown in a two-step proc ess. First, similar to 2000 Angstrom thick, amorphous Ba2CaCu2Ox and B a2Ca2Cu3Ox precursors are sputter-deposited onto LaAlO3(100) substrate s. Films are then thallinated and annealed using the crucible-pellet p rocess. With this method, it is possible to grow essentially single-ph ase Tl-1212, Tl-1223, Tl-2212, and Tl-2223 thin films. Under similar t hermodynamic conditions, we find that different phases dominate the fi lm growth as a function of reaction time. For example, the Tl-x212 pha ses generally nucleate first, and then, depending on growth conditions , convert to the Tl-1223 or Tl-2223 phase with extended annealing time s. We demonstrate that knowledge of both the thermodynamics and the ki netics of growth can yield high-quality films of each of the major Tl- superconducting phases.