SmFeAsO 1-x F x (Sm1111) tapes were prepared by an ex-situ powder-in-tube method with a Sn-presintering process. Scanning electron microscopy revealed apparent difference in microstructure between Sn-presintered tapes and the previously reported polycrystalline Sm1111 bulk, since Sn has reduced FeAs wetting phase and filled the voids between Sm1111 grains. The Sn-presintered tapes showed significant enhanced field dependences of transport J c compared with Sn-added tapes. A highest transport critical current density (J c ) of 3.45  10 4 A cm -2 at 4.2 K and self-field is achieved. Magneto-optical (MO) imaging further confirmed large and well-distributed global and intergranular J c in Sn-presintered Sm1111 tapes.

Monofilament MgB 2 /Fe wires or tapes were fabricated with two different purity crystalline boron powders, using internal magnesium diffusion (IMD) and in situ powder-in-tube (PIT) processes. To evaluate which method was more insensitive to the purity of the boron powders, a sensitivity factor was used. It was found that the IMD process was less sensitive to the purity of the boron powders, compared to the PIT method. Furthermore, J c values of the IMD-processed wires were higher than those of the PIT-processed samples. The reduced porosity and hence the increased density in the IMD-processed samples was thought to be the main reason. Although a number of B-rich particles remained in the MgB 2 region, a layer J c as high as 4.8×10 4 A cm −2 at 4.2 K and 10 T was still obtained in the IMD-processed wire, which was comparable to that of IMD-processed wires fabricated using amorphous boron powders.

Graphene is a special form of carbon which can effectively enhance the critical current density J c of MgB 2 . In this work, a systematic investigation on the impact of sintering conditions and doping level was carried out for graphene-doped MgB 2 tapes. It is found that an appropriate addition level, i.e., 8 at% in this work, is very critical to obtain a high J c in graphene-doped samples. The critical field and pinning force are improved obviously due to the graphene doping. The magnetic J c of samples sintered at 800 • C with 8 at% graphene doping reached 1.78 × 10 4 A/cm 2 , at 5 T, 20 K. At the same time, the transport J c was up to 2.38 ×10 4 A/cm 2 at 10 T, 4.2 K. The lattice distortion caused by C substitution and residual C at the grain boundaries were thought to be the major factors affecting the J c of graphene-doped MgB 2 samples.