Structural basis for enhancedTcinYBa2Cu3OyFx

Abstract

The optimum empirical formula and a model for the ordered crystalline motif for the high-$T_c$ (155 K), fluoride-substituted ceramic, Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_6$ ${\mathrm{F}}_2$ are deduced based on simple structural considerations. The average Cu-atom oxidation state (2.33) is predicted to be the same as in the oxygenated meterial ($T_c\sim 95$ K), Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$.