Effects of high-pressure sintering on critical current density in (Ba,K)Fe₂As₂ PIT wires

The effects of high-pressure sintering on the critical current density J_c in superconducting wires of (Ba_0.6K_0.4)Fe₂As₂ and (Sr_0.6K_0.4)Fe₂As₂ fabricated by the powder-in-tube technique were studied. The high-pressure sintering was conducted using the hot isostatic pressing (HIP) technique in a pressure up to 120 MPa. Local measurements on the magnetic induction distribution of the wire core in the critical state using magnetooptical imaging demonstrate that a uniform shielding current is flowing and intergranular couplings are very strong. Self-field J_c up to 1 × 10⁵ A/cm² is achieved in wires processed at 120 MPa and 700 °C. A systematic measurement of J_c in HIP-processed (Ba_0.6K_0.4)Fe₂As₂ wires demonstrates that J_c increases steadily with the pressure during the high-pressure sintering. On the other hand, the obtained J_c depends sensitively on the temperature during the high-pressure sintering, and the duration of the highpressure sintering also affects the value of J_c.