Orthorhombic-Tetragonal Phase Boundary in YBa₂Cu₃O_7-Δy

Abstract

The orthorhombic-tetragonal phase boundary in the ( Δ y - T ) diagram was determined by means of in situ X-ray diffraction methods for the YBa 2 Cu 3 O 7- Δ y . To cover the oxygen content region as widely as possible, two different methods were adopted. The first was performed under the fixed oxygen partial pressure and the second under the fixed oxygen content (deficiency Δ y ) of the samples. The obtained phase boundary showed a peculiar shape which differed from that proposed previously, suggesting the existence of another orthorhombic (ortho II) phase in low temperature region.