Ambient/low pressure synthesis and fast densification to achieve 55 KTcsuperconductivity in NdFeAsO0.75F0.25

55 K superconductivity in NdFeAsO 0.75 F 0.25 is demonstrated using two stage, ambient pressure synthesis (APS) with two zone temperature control for maintaining the As vapour pressure. The density of the APS material was subsequently increased by spark plasma sintering (SPS) for short times (60 s) at relatively low pressures (<80 MPa), giving density values above 95% of the theoretical value while maintaining very high slopes of upper critical field of up to 8.5 T K −1 . The APS+SPS method developed here is ideal for fabricating tapes in a rapid and safe way.