Determination of the Orthorhombic-Tetragonal YBa₂Cu₃O_7-δ Phase Boundary in the δ-T Diagram

Abstract

The orthorhombic-tetragonal YBa2Cu3O7-δ phase boundary in the δ-T diagram was determined by a detailed isobar TG measurement under the oxygen partial pressures of 1 to 0.01 atm. The phase boundary was found not to be located at δ = const., but to have a slope of dδ/dT∼-4.7×10-4 K-1. The experimental results are discussed with a simple order-disorder transformation model of oxygen atoms on the Cu plane sandwiched by Ba planes.

High-temperature superconductors YBaCu2O5 and Tl1.5BaCa2Cu2.5O8 with a decreased content of heavy metals (Ba and Tl)

“…After this, it was sintered in air at 900-960°C until the pellets decreased by 10-20%. Then the sam ples were calcined in oxygen at 500°C for 5-10 h. During such calcination, the maximal degree of oxi dation was attained [4]. inherent only in superconductors.…”

Synthesis and Characterization of High Temperature Properties of YBa2Cu3O6+δ Superconductor as Potential Cathode for Intermediate Temperature Solid Oxide Fuel Cells

“…Such behavior was already described by Jorgensen et al [31] as an oxygen-vacancy order-disorder phase transition. Jorgensen and other authors [31][32][33] investigated YBa 2 Cu 3 O 6+δ sample annealed at or above 900 °C demonstrating that oxygen partial pressure affects the transition temperature. It has been suggested that the phase transition is related to the oxygen content of the sample with the orthorhombic phase dominating at δ>0.5 while the tetragonal phase showing at δ<0.5.…”

Studies on the oxygen stoichiometry in superconducting cuprates by thermoanalytical methods

“…The structural phase transition is not located at any constant oxygen content value but depends on the pressure [18]. According to Kubo et al [19] the phase boundary has a slope of dy/dT =--4.7x10 -4 K-k In the REBa2Cu3OT_y system the transformation temperature tends to increase with decreasing ionic radii of the rare earth element [20]. Furthermore, the oxygen deficiency at the transformation point increases with increasing transformation temperature.…”