Correlation of T_c with the Rare Earth Size in (Ln)Ba₂Cu₃O_6+x Superconductors (Ln = La, Nd, Sm, Eu, Yb “ Cocktails”): Single Crystal X-Ray Diffraction and Electron Microscopy Studies

Abstract

In a previous paper, structural systematics around non-stoichiometric perovskite derivatives, YBa₂Cu₃O_9−n with n = 1, 2, 3, were developed implying Wadsley’s defects for the non-quantified n values [1]. In this series, YBa₂Cu₃O_6+x (with 0 ≤ x ≤ 1) exhibits remarkable superconductive properties and, in agreement with other reported results, a more precise domain has been found with T_c above 90 K for 0.66 ≤ x ≤ 1. This orthorhombic phase is associated with high T_c values. It is well known that at high temperature, it undergoes an orthorhombic → tetragonal phase transition accompanied by O₂ loss, this phenomenon being reversible.