Instrumental Analysis Center, Shanghai Jiao Tong University^* Department of Physics, Shanghai Jiao Tong University^**
○Qunli Rao^* Xin Yao^**

In order to study the superheating phenomenon during the melting process of YBa₂Cu₃O_7-δδ(YBCO) thin films, in-situ XRD measurements were explored around the peritectic temperature (T_p) of YBCO with a high temperature sample stage. As the temperature heating up from 850 ^oC to 1250^oC, several phase transformations take place in the YBCO thin-film on an MgO substrate. XRD analysis shows that Ba₂Cu₃O_5.9 phase was formed at the temperature 1100^oC, which indicates YBCO thin film can be substantially superheated above its T_p (1050^oC). In addition, Ba₂Cu₃O_5.9 has a certain oriented relationship with its parent phase YBCO.