Stability phase diagram of GdBa₂Cu₃O _7-δ in low oxygen pressures

We report the stability phase diagram of GdBa₂Cu ₃O_7-δ (GdBCO) in the low oxygen pressure (PO₂) regime of 1-100 mTorr. For this study, amorphous precursor films were deposited on the LaAlO₃ (LAO) (0 0 1) substrates at 200 °C by pulsed laser deposition (PLD), annealed at various high temperatures in low PO₂, and then quenched using a reel-to-reel tube furnace. By analyzing the phases and microstructures of the as-quenched films, the stability phase diagram of GdBCO could be accurately constructed. In the PO₂ regime of 20-100 mTorr, the GdBCO stability line on the log PO₂ versus 1/T (K^-1) diagram can be expressed by the equation of log PO₂ (Torr) = 10.85 - 13880/T (K), and unlike the well-known peritectic reaction of GdBCO Gd₂BaCuO₅ (Gd211) + Liquid (L) in high PO₂, a pseudobinary peritectic reaction of GdBCO Gd ₂O₃ + Liquid (L₁) occurs at the stability line of GdBCO. In the PO₂ regime of 1-10 mTorr, the GdBCO stability line can be expressed by the equation of log PO₂ (Torr) = 9.263 - 12150/T (K), and a ternary peritectic reaction of GdBCO Gd₂O₃ + GdBa₆Cu₃O_y (Gd163) + L₂ occurs at the stability line of GdBCO. In addition, a monotectic reaction of L₁ L₂ + Gd163 occurs at the phase boundary between Gd₂O ₃ + L₁ and Gd₂O₃ + Gd163 + L ₂.