Structure and magnetic properties of K$_{1-}$$_{\delta}$(Cu$_{1-x}$Fe$_{1+x}$)Se$_{2}$

In our attempt to synthesize new layered K$_{2-x}$Ba$_{x}$CuO$_{2}$Fe$_{2}$Se$_{2}$ hybrid materials [1] we have a new “122” selenide. Started from KO$_ {2}$, FeSe and a precursor of Ba$_{2}$CuO$_{3}$, put as pellets into alumina crucible and reacted at temperature 400-810 °C in sealed quartz tube under vacuum. The XRD show the presence of a tetragonal I4/mm phase, similar to the KFe$_{2-z}$Se$_{2}$ (K122) reported [2] mixed with Fe$_{3}$O$_{4}$ magnetite impurity. The a-axis is increased and c-axis decreased compared to K122, an indication of partial substitution of the cationic site. Our SEM and TEM study coupled to EDX confirm the I4/mm lattice and gives and average (K$_{0.63}$Ba$_{0.28}$)(Fe$_{0.46}$Cu$_{0.30}$)$_{2}$Se$_{2}$ composition. This compound is stable in air, on the contrary of the pure K-based 122 phase: it means that the Cu substitution and/or Ba substitution for K and Fe sites respectively stabilize the structure. In addition the electron diffraction patterns do not show signatures of Cu/Fe orderings, in similarity with K(MnAg)Se$_{2}$ compound [3]. The magnetization measurements show two transitions in addition to the one around 125K due to magnetite, a first one around 250K and another one at 50K. Superconductivity does not seem to be present in this selenide