Understanding the phase relations and cation disorder in LRE_1+xBa_{2− x}Cu₃O_7+δ

Abstract

Unlike Y123 which forms only a stochiometric compound, the light rare earth elements (LRE) form a solid solution LRE_1+xBa_2-xCu₃O_7+δ (LRE123ss), with increasing substitution of the LRE³⁺ for the Ba²⁺ with increasing ionic radii of the LRE. Charge balance is maintained by increasing oxygen occupation on the anti-chain sites. The range of solubility is partially controlled by the oxygen partial pressure (PO₂). The peritetic decomposition temperature also increases with increasing ionic radii. At doping levels of 0 > × > 0.1, there is an increase in T_c when the high temperature annealing (T ∼ 940‡C) is performed in low PO₂ (> 0.1 bar). The maximum T_c occurs at a doping level of ∼x < 0.05 for Nd and Gd. When annealing is performed in 1 bar PO₂, there is a gradual decrease in T_c with increasing x. These phenomenon can be understood in terms of the number and distribution of the LRE which substitute on the Ba site.