The O non-stoichiometry and diffusion in SmBa2Cu3−xAlxO6+δ superconductor were investigated by means of thermogravimetric analysis over wide PO2 (1 to 10−4atm) and temperature (400 to 800C) ranges. Thermogravimetric data at fixed O partial pressures were collected by using temperature steps and long isotherms. The samples used for thermogravimetric analysis were previously sieved in order to obtain powders of known particle dimensions. This procedure allowed to determine both the O non-stoichiometry and its diffusion coefficient in SmBa2Cu3−xAlxO6+δ. With respect to undoped SmBa2Cu3O6+δ, the corresponding δ values were quite similar in oxidising conditions, while the doped material loses less O than the pure one in reducing conditions. For what concern the O diffusion, Al doping did not affect the activation energy for that process; on the opposite the absolute D value was at least one order of magnitude lower than in the pure phase and the D varied as a function of PO2. All of the above features were interpreted under the hypothesis that, in the thermodynamic conditions of the experiments, only O4 O ions and sites surrounded by two Cu1 ions were involved into gas–solid equilibria and into diffusion process.

Transport Properties of Al-Doped SmBa2Cu3O6+δ Superconductor – I, Oxygen Non-Stoichiometry and Diffusion. M.Scavini, L.Malavasi, L.Mollica: Solid State Sciences, 2004, 6[11], 1187-94