High-Pressure Synthesis of New Fe-based Superconductors

Abstract

  In this article, availability of high-pressure technique to synthesize oxygen-deficient LnFeAsO_1-y (Ln: lanthanide elements) and (Ba, K)Fe₂As₂ samples is demonstrated. It is found out that the synthesis pressure is an important parameter for synthesizing single-phase samples, in particular for the heavier Ln's, such as Tb and Dy. The lattice parameters systematically decrease with the atomic number of Ln, reflecting the shrinkage of Ln ionic radius. For the lighter Ln's (La, Ce, Pr, Nd), T_c increases monotonously with decreasing the lattice parameters from 26 K for Ln=La to 54 K for Ln=Nd, then stays at the constant value around 53 K for the heavier counterpart (Nd, Sm, Gd, Tb and Dy).