Low-temperature synthesis to achieve high critical current density and avoid a reaction layer in SmFeAsO_1-xF_x superconducting tapes

A low-temperature (300-500 °C) heat treatment process under ambient pressure or uniaxial pressure was performed on Sn-added SmFeAsO_1-xF_x superconducting tapes fabricated by the ex situ powder-in-tube method. A highest transport critical current density (J _c) of 3.95 × 10⁴ A cm^-2 (at 4.2 K and self-field) was achieved by this process. The low-temperature process allows tapes to endure much longer heat treatment without J _c degradation than the high-temperature method. Microscopic analysis also revealed that this method could obtain a clear boundary without a reaction layer or interdiffusion between a superconducting core and sheath metal.