Preparation of Y 2Ba 4Cu 8O 16 thin films by electron-beam evaporation and the effect of hydrogen charging

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The BaF 2 method was used to prepare Y 2Ba 4Cu 8O 16 thin films. Cu and Y were evaporated by electron guns and BaF 2 by an effusor. The flour-oxygen exchange was performed at 800°C in wet oxygen. The resulting film contained mainly the 248 phase but the 123 phase was also present. Hydrogen charging was performed at 190° C in a H 2 pressure of 100 mbar. The X-ray diffraction diagram after 135 h hydrogen charging showed still the (001) reflections typical for the c-axis riented film. However, the lines were shifted corresponding to a 1.4% increase of the c-axis and reflections with odd l's appeared besides the even-l reflections, the only ones seen in the uncharged film. Implications of these observations on the structure of the hydrogenated films are discussed.