Structural and chemical evolution of propionate based metal-organic precursors for superconducting YBa2Cu3O7-δ epitaxial film growth

The structural and chemical evolution of propionate based low fluorine YBa2Cu3O7-delta (YBCO) precursor during the conversion thermal treatment to obtain superconducting film has been investigated by both x-ray photoelectron and diffraction techniques in a set of partially converted films on SrTiO3 single crystals. The pyrolysis temperature within the range 400-480 degrees C mainly affects the copper valence state with an increase of the Cu2+ fraction with temperature with respect to the Cu1+ oxidation state. During the subsequent thermal treatment up to 700 degrees C, the reduction of fluorine content is mainly ascribed to the hydrolysis of YF3. At higher temperatures, Ba hydrolysis, Y2Cu2O5 and YBCO phase formation (nucleation at 700 degrees C and 725 degrees C, respectively) have been observed. The temperature dependences of the formation and decomposition of YBCO, Y2Cu2O5 and Ba-oxyfluoride were evaluated by x-ray diffraction measurements. The reaction path emerging from these analyses agrees with the one observed for YBCO films obtained with the standard MOD method based on metal tri-fluoroacetate precursors.