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 4.2 K 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.