In-Field Thermal Conductivity of Ag and Cu/Ag Ba1-xKxFe2As2 Composite Conductors

This work reports the longitudinal thermal conductivity,
κ,
of Ag- and Cu/Ag-sheathed Ba
_1-x
K
_x
Fe
₂
As
₂
conductors. Our investigation has been carried out between 4 K and 80 K with magnetic fields up to 19 T. In the case of Ag-sheathed tapes, the thermal conductivity reaches maximum values of ∼80 Wm
⁻¹
K
⁻¹
and is weakly dependent on the field. The use of Cu/Ag in the place of Ag allows increasing
κ
up to ∼250 Wm
⁻¹
K
⁻¹
. Zero-field
κ
values are about one order of magnitude lower than those achieved in other technical superconductors that employ a silver matrix, as Bi
₂
Sr
₂
CaCu
₂
O
_8+
x
(Bi2212) and Bi
_2−x
Pb
_x
Sr
₂
Ca
₂
Cu
₃
O
_10−x
(Bi2223). This is a consequence of the contamination of the metal sheaths because of elemental diffusion occurring during the tape sintering. The differences in
κ
between the Ba
_1-x
K
_x
Fe
₂
As
₂
tapes and the other technical superconductors with an Ag matrix become smaller at high field. We suggest that performing the sintering at high pressure could represent a way to reduce the elemental contamination and thus improving the thermal conductivity.