Real-time observation of the melting process of YBCO thin film on MgO substrate

In order to study the mechanism of the liquid phase hetero-epitaxial growth, the melting process of YBa2Cu3O7-*d (YBCO) thin films was observed by high temperature optical microscopy. During the heating from room temperature to a temperature above the YBCO peritectic temperature (Tp), we surprisingly find that the YBCO thin film with a MgO substrate can be substantially superheated above the Tp of the YBCO oxide (at least 50DGC) at a heating rate of 5 deg C min-1. This is a novel superheating phenomenon involved in a peritectic reaction and an oxide material, which is different from one reported in systems of metals and their alloys. After the melting process, x-ray diffraction analysis was performed, which shows that Y2BaCuO5 (Y211) grains are in good alignment on the MgO substrate. The superheating mechanism of the YBCO oxide is discussed.