Shape Control Mechanism in RE123 LPE Films for Persistent Current Switch Material

Many applications of the superconducting magnets using high-Tc oxide superconductors are expected to operate in a persistent current (PC) mode. For the PC mode operation, a PC switch (PCS) is considered to be an essential device. The special properties are required for the PCS material, which is not only a high critical current but high electric resistance in the normal state in order to cut off the current flow efficiently through switching.The liquid phase epitaxy (LPE) method could afford REBa2Cu3Oy (RE123) thick films with a high critical current density in the superconducting state and a reasonable electric resistivity in the normal state. However, the long current pass is necessary to achieve a required value for the application such as several ohms of its electric resistance. In this study we have studied to fabricate a meander shaped LPE film to realize a high electric resistance in the normal state. The seed film on an MgO single crystalline substrate was shaped into a meander type by the chemical etching method and dipped into the solution for the LPE growth. The meander shaped RE123LPE film with a long current path on the MgO substrate of 2 inches in diameter could be successfully grown. This phenomenon could be explained by the change of the growth mode in the side wall from step growth to that limited by the nucleation on a(b)-c plane. This is introduced by the small step-advancing rate of the RE123 crystal on the MgO surface and above the dissolved MgO substrate. The film revealed a high resistance value of 1.7 Ω at 100 K.