Stability of Bi 2 Sr 2 Ca 1 Cu 2 O 8 ±δ Thick Films at Elevated Oxygen Pressures and Temperatures

Bi 2 Sr 2 Ca 2 Cu 2 O 8±δ ‐type compound thick films were exposed to oxygen‐argon‐gas mixtures (1% to 20% oxygen gas) at elevated pressures (up to 207 MPa) and temperatures (500° to 940°C) for times ranging from 5 to 96 h. At a sufficiently high oxygen fugacity and temperature, Bi 2 Sr 2 Ca 1 Cu 2 O 8±δ decomposed via a solid‐state reaction. Room‐temperature X‐ray diffractometry and electron probe microanalysis of decomposed films revealed the presence of Bi 2 (Sr,Ca) 2 ‐Cu 1 O 6±θ ro‐type compound, Bi 2 Sr 2 ,Ca 1 O 8±δ ‐type compound, and CuO. Bi 2 Sr 2 Ca 1 Cu 2 O 8±δ decomposition was accompanied by a modest weight gain, which was consistent with an oxidation reaction. The solid‐state decomposition reaction could be reversed by heat treatment of decomposed films at 860°C in pure, flowing oxygen at ambient pressure.