The dependence of the degree of nonstoichiometry of YBa 2 Cu 3 0 7–x (123) on temperature and oxygen pressure has been determined by thermogravimetric analysis (TGA) in the temperature range 400° to 950°C and the oxygen pressure range 10 –6 to 1 atm (1 atm = 10 5 Pa). The nature of the decomposition of 123 in the temperature range 750° to 950°C and the oxygen pressure range 10 –6 to 10 –2 atm has been determined by TGA and X‐ray diffractometry (XRD). As the oxygen pressure decreases, the decomposition of 123 follows the sequence 123→ Y 2 BaCuo 5 (211) + BaCuO 2 ° Cu 2 O→ 211 ° BaCuO 2 ° BaCu 2 O 2 → 211 ° YBa 3 Cu 2 O x (132) ° BaCu 2 O 2 → 211 ° BaCu 2 O 2 °BaO. The incongruent melting temperatures have been determined in the oxygen pressure range 10 –6 to 1 atm by differential thermal analysis, and the phases formed on solidification have been identified by XRD. The stability diagram for the composition 123 has been constructed.
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Kim et al. (1994) studied this question.