Stability phase diagram of GdBa2Cu3O7−δ in low oxygen pressures

Abstract

We report the stability phase diagram of GdBa2Cu3O7−δ (GdBCO) in the low oxygen pressure (PO2) regime of 1–100mTorr. For this study, amorphous precursor films were deposited on the LaAlO3 (LAO) (001) 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 20–100mTorr, 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 1–10mTorr, 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.