Gibbs’ energy of formation of YBa₂Cu₃O_7-x (tetragonal)

Abstract

The high temperature ceramic oxide superconductor YBa₂Cu₃O_7-x (1–2–3 compound) is generally synthesized in an oxygen-rich environment. Hence any method for determining its thermodynamic stability should operate at a high oxygen partial pressure. A solid-state cell incorporating CaF₂ as the electrolyte and functioning under pure oxygen at a pressure of 1·01 × 10⁵ Pa has been employed for the determination of the Gibbs’ energy of formation of the 1–2–3 compound. The configuration of the galvanic cell can be represented by: Pt, O₂, YBa₂Cu₃O_7-x , Y₂BaCuO₅, CuO, BaF₂/CaF₂/BaF₂, BaZrO₃, ZrO₂, O₂, Pt. Using the values of the standard Gibbs’ energy of formation of the compounds BaZrO3 and Y2BaCuO5 from the literature, the Gibbs’ energy of formation of the 1–2–3 compound from the constituent binary oxides has been computed at different temperatures. The value ofx at each temperature is determined by the oxygen partial pressure. At 1023 K for O content of 6·5 the Gibbs’ energy of formation of the 1–2–3 compound is −261·7 kJ mol⁻¹.