Stability phase diagram of GdBa2Cu3O7−δ in low oxygen pressures

We report the stability phase diagram of GdBa2Cu3O7−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 ↔ Gd2O3 + 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 + GdBa6Cu3Oy (Gd163) + L2 occurs at the stability line of GdBCO. In addition, a monotectic reaction of L1 ↔ L2 + Gd163 occurs at the phase boundary between Gd2O3 + L1 and Gd2O3 + Gd163 + L2.