Aliovalent Substitution in 1144 Iron Based Superconductors: Effect on Structure and Superconducting Properties

Ca/K-1144 compounds have been described widely in literature as stoichiometric compounds, with a Ca:K ratio equal to unity. In this work, we demonstrate that Sr ions can substitute K ions in the 1144 lattice. Polycrystalline samples were produced via a mechanochemically assisted synthesis route. Sr substitution in the Ca/K compound leads to a shortening of its
c
axis, while no differences are appreciable from the morphological point of view. The CaK
_0.9
Sr
_0.1
Fe
₄
As
₄
compound is characterized by a slightly reduced critical temperature of approximately 31 K, with respect to the 35 K of the pristine compound. The role of lattice distortion carrier concentration or structural disorder that may be accounted for the reduction of critical temperature is here discussed.