Demonstration of Excellent J c Performance in ( AE ,Na)Fe 2 As 2 ( AE : Sr, Ba) PIT Wires

Na-substituted 122-type iron-based superconductors were synthesized and fabricated into superconducting tapes and wires. Good J c performance of Ag-sheathed Sr 0.45 Na 0.55 Fe 2 As 2 pressed tapes was demonstrated, and it was further improved by using AgSn as a sheath material. The improved J c characteristics are due to the reduction of the optimum sintering temperature by ∼100 °C, which suppressed the reaction between the sheath and the core. However, the fabrication of good Sr 0.45 Na 0.55 Fe 2 As 2 round wire using the hot isostatic press method failed, due possibly to the segregation of Na in the core. To avoid the segregation of Na, we fabricated round wires employing (Ba,Na)Fe 2 As 2 rather than underdoped (Sr,Na)Fe 2 As 2 . J c in Ba 0.6 Na 0.4 Fe 2 As 2 round wire processed 700 °C under the pressure of 175 MPa reached 1.5 × 10 5 and 2.0 × 10 4  A/cm 2 at self-field and 100 kOe, respectively. These values are more than fifty percent of the largest J c in (Ba,K)Fe 2 As 2 round wires, demonstrating the excellent performance of (Ba,Na)Fe 2 As 2 wires.