Effects of reducing and oxidizing thermal treatments on epitaxial Bi 2.1-xPbxSr2.9-yCayCu 2O8+z films

We have studied the effects of reducing and oxidizing thermal treatments on truly epitaxial Bi2.1-xPbxSr2.9-yCayCu2O8+z films. Films were grown on NdGaO3 substrates by liquid phase epitaxy with a very narrow mosaic spread (less than 0.1-degrees). Transport and structural properties were investigated for a number of films after various annealing treatments. T(c) is shifted to higher values by reducing treatments and to lower values by oxidizing treatments for all lead concentrations. For all films the maximum range of variation T(c)max - T(c)min is about 15 K. However, the T(c) for the as-grown lead doped films is lower relative to the undoped ones. Furthermore, in the case of doped films, the optimum hole concentration (corresponding to the highest T(c) of 94 K) cannot be reached by reducing treatments. For both doped and undoped films the c-lattice parameter was found to increase slightly after reducing treatments