Effect of Oxygen Loss on Densification When Hot Isostatic Pressing YBa2Cu3O7−δ

Hot isostatic pressing of the high-T_c superconductor YBa₂Cu₃O_7?δ can lead to loss of oxygen and transformation of the material from the high-T_c orthorhombic phase to the nonsuperconducting tetragonal phase. It is shown that glass encapsulation helps retain the orthorhombic structure, whereas steel encapsulation resulted in formation of the tetragonal phase. Reasons for this phenomenon are discussed. The equilibrium oxygen gas pressure for the oxygen decomposition reaction in YBa₂Cu₃O₇, however, prevents full densification of this material in glass when employing hot isostatic pressing conditions of 200 MPa and 845°C.