Structural and chemical evolution of propionate based metal–organic precursors for superconducting YBa₂Cu₃O_{7 − δ}epitaxial film growth

Abstract

The structural and chemical evolution of propionate based low fluorine YBa 2Cu 3O 7 - δ (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 SrTiO 3 single crystals. The pyrolysis temperature within the range 400-480 °C mainly affects the copper valence state with an increase of the Cu 2 + fraction with temperature with respect to the Cu 1 + oxidation state. During the subsequent thermal treatment up to 700 °C, the reduction of fluorine content is mainly ascribed to the hydrolysis of YF 3. At higher temperatures, Ba hydrolysis, Y 2Cu 2O 5 and YBCO phase formation (nucleation at 700 °C and 725 °C, respectively) have been observed. The temperature dependences of the formation and decomposition of YBCO, Y 2Cu 2O 5 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