Solid-liquid phase equilibria on the GdBa₂Cu₃O_7-δ stability phase diagram in low oxygen pressures (1-100 mTorr)

We report the solid-liquid phase equilibria on the GdBa₂Cu₃O_7-δ (GdBCO) stability phase diagram in low oxygen pressures (PO₂) ranging from 1 to 100 mTorr. On the basis of the GdBCO stability phase diagram experimentally determined in low oxygen pressures, the isothermal sections of three different phase fields on log PO₂ vs. 1/T diagram were schematically constructed within the Gd₂O₃-Ba₂CuO_y-Cu₂O ternary system, and the solid-liquid phase equilibria in each phase field were described. The invariant points on the phase boundaries include the following three reactions; a pseudobinary peritectic reaction of GdBCO ↔ Gd₂O₃ + liquid (L₁), a ternary peritectic reaction of GdBCO ↔ Gd₂O₃ + GdBa₆Cu₃O_y + liquid (L₂), and a monotectic reaction of L1 ↔ GdBa₆Cu₃O_y +L₂. A conspicuous feature of the solid-liquid phase equilibria in low PO₂ regime (1-100 mTorr) is that the GdBCO phase is decomposed into Gd₂O₃ + L₁ or Gd₂O₃ + GdBa₆Cu₃O_y + L₂ rather than Gd₂BaCuO₅ + L well-known in high PO₂ like air.