Abstract
We have studied in detail the kinetics aspects ofY Ba2Cu3O7−x (YBCO)thinfilm growth on LaAlO3(100) single crystals by the sol–gel TFA-MOD method, using an in situ fluorideselective electrode. Kinetics curves show that an intermediate step existsbefore the YBCO formation. This step, which starts at a lower temperaturethan YBCO formation, consists in a partial elimination of F from theBaF2 precursorto form an oxyfluoride intermediate compound. The total YBCO formation appears at temperatures ashigh as 700 °C and the activation energy of the reaction is . We have found that at low flow carrier gas rates, the reaction is controlledby diffusion mechanisms and the apparent order of YBCO formation isn = 1 with respect to the stirring rate, but at higher flow rates the YBCO formationis controlled chemically, then the apparent order is zero. The apparentEa for the oxyfluoride formation at lower temperatures corresponding to the intermediate stepis only and the oxyfluoride rate formation increases with the stirring rate, indicating that thisintermediate reaction is controlled by diffusion mechanisms.
Published Version
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