Influence of Rare-Earth Inclusion on Structure and Properties of Ca/K-1144 IBSC

Abstract

Among Iron Based superconductors (IBSC), the compounds belonging to the 1144 family are characterized by the A1AE1Fe4As4 chemical composition (A = Alkaline, AE = Alkaline-Earth) and considered stoichiometric. In recent experiments, we obtained 1144 samples characterized by different levels of alkali and alkaline earth metals substitutions and demonstrated how the lattice distortion induced by such variation in the chemical composition plays a fundamental role on critical temperature values. In this work, we investigate the possibility to obtain Ca/K-1144 compounds substituted with Rare-Earth (RE) elements. We produced polycrystalline samples in which RE ions partially replace Ca ions in the 1144 phase. The lattice structure is consistently affected by the substituent element inducing a contraction of the c-axis. Multiple substitution of RE and A or AE elements was also attempted, showing that appropriate combinations allow simultaneous inclusion of different elements in the structure. For compounds that include RE elements, the critical temperature of the samples appears to follow to the same trend with respect to the distortion of the crystal lattice induced by A and AE substitutions.