High-temperature phase equilibria near YBa₂Cu₃O_6+x

The quaternary phase relations near YBa2Cu3O6+x were investigated using a solid-state ionic technique. Three invariant reactions were discovered. At 850°C, YBa2Cu3O6+x with excess Cu2O reacts to form Y2BaCuO5 and BaCu2O2 at 1×10-3 atm oxygen, while pure YBa2Cu3O6+x decomposes to Y2BaCuO5, BaCu2O2, and YBa3Cu2O6.5±x at 4×10-4 atm oxygen. These results show that the phase relations near YBa2Cu3O6+x change markedly with oxygen pressure. © 1989.