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 (Ba0.6K0.4)Fe2As2 and (Sr0.6K0.4)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 x 10(5) A/cm(2) is achieved in wires processed at 120 MPa and 700 degrees C. A systematic measurement of J(c) in HIP-processed (Ba0.6K0.4)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 high-pressure sintering also affects the value of J(c).