First- and second-order phase transitions and oxygen rearrangement over the Cu1-O4 chains in orthorhombic YBa2Cu3O6+x at low temperatures

✍ Scribed by L.G. Mamsurova; K.S. Pigalskiy; V.P. Sakun; A.I. Shushin; L.G. Scherbakova

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 808 KB
• Volume: 167
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(90)90479-x

✦ Synopsis

The thermodynamics of a system of oxygen ions ordered along the 04 chains in the Cul-04 basal plane of orthorhombic YBa2Cu$&+x is theoretically studied using a modified mean field approximation. This allows the "intrachain" thermodynamics to be treated exactly, although interchain oxygen-oxygen correlations are ignored. Such an approach is justified only when interchain correlations are much weaker than those within the chains. Four different types of thermodynamically stable oxygen ordering are predicted with this model. They are featured by la,, 2a,, and 3% periodicity along the crystallographic a-direction. The first-and second-order phase transitions between these phases can occur at low temperatures and high oxygen content. The T,xphase diagram calculated serves as a basis for the explanation of the experimental findings concerning elastic modulus temperature hysteresis and the anomaly in the acoustic loss spectra at T-300 K in YBazCu 3 0 6+X samples with various oxygen contents.