Development and Characterization of P-doped Ba-122 Superconducting Tapes

Among the recently discovered Fe-based superconducting compounds, the Ba-122 phase has proved to be the more attracting for the development of powder in tube (PIT) processed conductors. In fact, after some years of development, critical current densities ($J_{c}$) of about $10^{5} A/cm^{2}$ at 4.2 K and magnetic fields up to 10 T have been obtained in$(Ba_{0.6} K_{0.4}) Fe_{2} As_{2}$, PIT wires and tapes. To develop a safe upscaling method, the synthesis of the powders is a crucial point. In order to avoid the use of highly reactive K we have developed $BaFe_{2}(P_{1-x}As_{x})_{2}$ PIT tapes. This compound has proved to be very stable and in form of crystals and thin films exhibits excellent critical current: We succeeded in manufacturing PIT tapes with this phase with $J_{c}$ values of about $10^{3}A/cm^{2}$ at 4.2K in self-field. Detailed microstructural and chemical investigations of the samples have been performed by high-resolution TEM, scanning TEM, and electron energy loss spectrometry analysis. A deformation network inside the grains that can induce strong pinning has been observed. However, chemical inhomogeneities at the grain boundaries are also present, which limit the transport current.