Phase equilibria in La(Y)-Ba-Cu-O systems and growth of high-T/sub c/ superconductor bulk single crystals

Abstract

The isobaric phase diagrams of BaO(La203)-CuO-C U O~.~ systems at a partial oxygen pressure of 0.021MPa, the phase transition Ba02f BaO at oxygen pressure up to 2.1 MPa have been studied and a flux method for growing bulk single crystals of YBa2Cu307-g, La2Cu04, (LaSr)2Cu04, Nd2Cu04 and (NdCe)2Cu04 has been developed using a rotatable crucible which ensures separation of crystals from the melt .

Thermodynamic Modeling of the Binary Barium–Oxygen System

“…and Mayorova et al 27 . Additionally, the evidence offered by Aptekar et al ., 16,17 Emelchenko et al ., 26 and Mayorova et al 27 . against the presence of the liquid phase at 1071K is more compelling since these experiments were done over a wide range of pressures, as opposed to the 1 atm experiments by Hedvall 24 and Kedrovskii et al 25 .…”

“…using DTA, X‐ray diffraction (XRD) and thermogravimetery. They found the BaO, BaO 2 , and gas three‐phase equilibrium at the temperature around 1090 K 16,17,26 and did not observe the appearance of liquid. Moreover, Aptekar et al 16,17 .…”

“…Moreover, Aptekar et al 16,17 . and Emelchenko et al 26 . established the pressure‐temperature ( P‐T ) relationship for the BaO, BaO 2 , and gas three‐phase equilibrium for temperatures up to 1345 K. Since the experimental ln P versus 1/ T relationship did not change its slope over the studied pressure and temperature ranges, the authors 16,17 concluded that this relationship represented the same BaO, BaO 2 , and gas three‐phase equilibrium and that the liquid phase did not participate in any invariant reactions with BaO and gas at least up to 1345 K and 20 atm.…”

“…investigated the phase boundaries of the BaO–BaO 2 two‐phase region and observed the appearance of the gas and liquid phases at 1071 K. The phase relation in the composition range between the BaO and gas phases was further investigated by Aptekar et al 16,17 . using a thermogravimetry apparatus, and by Emelchenko et al 26 . using DTA, X‐ray diffraction (XRD) and thermogravimetery.…”

“…against the presence of the liquid phase at 1071K is more compelling since these experiments were done over a wide range of pressures, as opposed to the 1 atm experiments by Hedvall 24 and Kedrovskii et al 25 . Consequently, the experimental P versus T results by Aptekar et al ., 16,17 Emelchenko et al ., 26 and Mayorova et al 27 . were used in the present work, while the liquid→BaO+gas equilibrium temperature at 1071 K 24,25 was discarded.…”