The mechanism for the formation of α-axis phase in high-J_c Sm_1+xBa_2-xCu₃O_y thick films prepared by low temperature growth technique

REBa₂Cu₃O_y (REBCO) film is required for high-critical current (I_c) at 77 K, when using in power applications such as superconducting magnetic energy storage (SMES) and nuclear fusion. Generally, critical current density (I_c) of REBCO thick film decreases with increasing thickness of superconductor, because the amount of dead layer such as a-axis oriented phase increases with increasing the thickness. We speculated that the formation of α-axis oriented phase in REBCO thick films is owing to reduction of surface temperature. In this study, we fabricated low temperature growth (LTG)-multi Sm_1.04Ba _1.96Cu₃O_y, (SmBCO) thick films using a (Sm _1.04Ba_1.96Cu₃O_y/Sm-rich layer) × N (N= 1, 2⋯) multilayer system, to suppress the formation of α-axis oriented phases. The LTG-multi thick films retained a large terrace, as a result, supressing the reduction of surface temperature, even if the thickness of the films becomes thick. Therefore, LTG-multi thick films suppressed the formation of a-axis oriented phases and the films showed I _c = 630 A/cm-width with a thickness of 1.35 μm at 77 K, From these results, we suggest that LTG-multilayer system is an effective technique for improving the critical current of coated conductor.