On the Phase Relation between Two Polymorphs of Ba_1.8Y_1.2Cu₃O_6.7-δ and Their Oxygen Contents

Abstract

The relation between the oxygen deficiency δ and the the two polymorphs of Ba 1.8 Y 1.2 Cu 3 O 6.7-δ , i.e., orthorhombic and tetragonal phases, have been studied by the gravimetric method combined with the X-ray diffraction analysis. The oxygen deficiency δ was varied by annealing the samples in an argon or oxygen atmosphere at an appropriate temperature, followed by rapid quenching to room temperature. It is shown that the tetragonal phase is characterized by a large oxygen defficiency, δ=0.6-0.7, suggesting that oxygen occupancy factor at z =1/2 of the structural model proposed by Siegrist et al . [submitted to Phys. Rev. lett.] is nearly zero.