STABILITY DIAGRAM FOR THE SYSTEM YBA2CU3O7-X

The dependence of the degree of nonstoichiometry of YBa2Cu3O7-x (123) on temperature and oxygen pressure has been determined by thermogravim etric analysis (TGA) in the temperature range 400-degrees to 950-degre es-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- degrees to 950-degrees-C and the oxygen pressure range 10(-6) to 10(-2 ) atm has been determined by TGA and X-ray diffractometry (XRD). As th e oxygen pressure decreases, the decomposition of 123 follows the sequ ence 123 --> Y2BaCuO5 (211) + BaCuO2 + Cu2O --> 211 + BaCuO2 + BaCu2O2 --> 211 + YBa3Cu2Ox (132) + BaCu2O2 --> 211 + BaCu2O2 + BaO. The inco ngruent melting temperatures have been determined in the oxygen pressu re range 10(-6) to 1 atm by differential thermal analysis, and the pha ses formed on solidification have been identified by XRD. The stabilit y diagram for the composition 123 has been constructed.