Phase equilibria in the PrBaCuO system under varied oxygen partial pressures

Abstract

Phase equilibria in the PrBaCuO system under varied oxygen partial pressure ( pO 2) is investigated. Stoichiometric PrBa 2Cu 3O 7−δ (Pr123) does not exist for pO 2 < 1 bar O 2. Instead, nominal Pr123 is a mixture of Pr 1+ x Ba 2− x Cu 3O 7+δ solid-solution (Pr123 ss) and BaCuO 2. When nominal Pr123 is processed at 900°C in 1 bar O 2, the lower limit for x is 0.04. As the pO 2 is lowered, the occupancy of the Pr ions on the Ba sites is decreased. The minimum lower limit of x is ∼ 0.01 at 900°C using a pO 2 of 0.001 atm. Further reducing the pO 2 causes the BaCu 2O 2 and PrBaO 3 phases to form.