Effect of doping elements on electric properties of RE123 LPE films for PCS materials

We have studied fabrication of Zn-doped REBa2Cu3Oy(RE123) films prepared by liquid phase epitaxy (LPE) to control the critical temperature (Tc) as persistent current switch (PCS) materials, and to investigate the effect of Zn-doping on electric properties of RE123 LPE films. Through the calculation of the initial transient growth in the LPE, it was found that the initial transient thickness is very thin as to be less than 0.1 μm. This means that the inhomogeneous region of Zn concentration in the LPE film due to this non-steady-state growth could be negligible for Tc uniformity. Additionally it was also derived that the Tc controllability by Zn-doping in the LPE system is extremely high since the effective distribution coefficient (ke) was almost the same as the equilibrium one (k0), which means the ke rarely depends on the growth conditions such as the growth rate. Concerning the required properties for PCS, the Jc value of the Zn-doped RE123 LPE film with an H shape is very low because of Mg contamination in the LPE film from dissolution of the used MgO substrates. This problem was solved by inserting a BaZrO3 buffer layer to prevent from dissolution of the MgO substrates. The product of Jc (at 20 K, 3 T) and normal resistivity of the Zn-doped LPE film on the BZO buffer layer was slightly lower than that of the non-doped LPE film on the BZO buffer layer, but Tc of the Zn-doped LPE film is about 30-50 K lower than that of the non-doped one. This means that the Zn-doped LPE film has an advantage of the capability of the quick response for switching with maintaining the PCS performance.