On the thermodynamics of Barium Oxyfluoride precursor in YBCO growth via MOD process

Abstract

Barium Oxyfluoride plays an important role, as precursor species, in the nucleation and growth of YBa2Cu3O7-δ (YBCO) via the low fluorine Metal Organic Decomposition (MOD low-fluorine) route. In this contribution, we present a study on the thermodynamics of the Oxyfluoride by processing experimental data on the YBCO growth at LaAlO3 (LAO) substrate. The analysis allows one to determine the standard enthalpy and the standard entropy changes for Oxyfluoride formation from Barium oxide and Barium fluoride. To identify the thermodynamically more favorable route to the Oxyfluoride formation in the MOD low-fluorine process, the free energy change for the formation of the precursor, through reactions involving gas water, has been determined. The free energy of formation via fluoride and water indicates higher stability of oxygen rich Oxyfluoride for (P_HF^2)/P_(H_2 O) <10^(-6). In the framework of the nucleation theory the present results are needed to study the effect of precursor composition on film orientation.