  Ag-sheathed CaKFe4As4 superconducting tapes have been fabricated via the
ex-situ powder-in-tube method. Thermal and X-ray diffraction analyses suggest
that the CaKFe4As4 phase is unstable at high temperatures. It decomposes into
the CaAgAs phase which reacts strongly with the silver sheath. We therefore
sintered the tape at 500C and obtain a transport critical current density
Jc(4.2 K, 0 T)~ 2.7x10^4 A/cm2. The pinning potential derived from
magnetoresistance measurements is one order of magnitude lower than that of the
(Ba/Sr)1-xKxFe2As2 tapes. Combining with the scanning electron microscopy and
magneto-optical imaging results, we suggest that bad connectivity between
superconducting grains caused by the low sintering temperature is the main
factor responsible for the low Jc. However, this system is still a promising
candidate for superconducting wires and tapes if we further optimize the
post-annealing process to achieve better grain connectivity.
