Stability Diagram of YBa2Cu3O7-δ in Low Oxygen Pressures

We report the phase stability of YBa
₂
Cu
₃
O
_7-δ
(YBCO) in low oxygen pressure (P O
₂
) region of 1-900 mTorr. For this study, the amorphous Y-Ba-Cu-O precursor films were deposited on LaAlO
₃
(LAO) (001) substrate at 200°C by pulsed laser deposition. As-deposited precursor films were annealed at various high temperatures in a given PO
₂
, quenched using a reel-to-reel furnace, and then their phases and microstructures were analyzed to accurately determine the stability line of YBCO and its decomposition reaction. The stability line of YBCO in the PO
₂
regime of 1-200 mTorr on the PO
₂
versus 1/T diagram can be expressed by the equation of Log PO
₂
(Torr) = 9.79 - 11 783/T (K
^-1
), and the ternary peritectic decomposition of YBCO ↔ Y
₂
O
₃
+ YBa
₃
Cu
₂
O
_6.5
(Y132) + Liquid(L
₁
) occurs at the stability boundary. In 250-900 mTorr, it can be expressed by the equation of Log PO
₂
(Torr) = 12.67 - 15 276/T (K
^-1
), and the ternary peritectic decomposition of YBCO ↔ Y
₂
BaCuO
₅
(Y211) + Y132 + Liquid (L
₂
) occurs at the stability boundary.