title: Liquidus Diagram of theBa-Y-Cu-OSystem in the Vicinity of theBa2YCu3O6+xPhase Field.
abstract: This paper describes the melting equilibria in the vicinity of the highTcphase Ba2YCu3O6+x, including evidence for two Ba-Y-Cu-O immiscible liquids. Melting equilibria have been investigated in purified air using a combination of differential thermal analysis (DTA), thermogravimetric analysis (TGA), powder x-ray diffraction (XRD), MgO wick entrapment of liquid for analysis, scanning electron microscopy (SEM) coupled with energy dispersive x-ray analysis (EDS), and hydrogen reduction for determination of copper oxidation state. For relatively barium-rich compositions, it was necessary to prepare the starting materials under controlled atmosphere conditions using BaO. A liquidus diagram was derived from quantitative data for the melts involved in various melting reactions. In general the 1/2(Y2O3) contents of the melts participating in these equilibria were low (mole fraction <4 %). The primary phase field of Ba2YCu3O6+xoccurs at a mole fraction of <2.0 % 1/2Y2O3and lies very close along the BaO-CuOxedge, extending from a mole fraction of ≈43 % CuO to a mole fraction of ≈76 % CuO. It is divided by a liquid miscibility gap and extends on either side about this gap. The topological sequence of melting reactions associated with the liquidus is presented as a function of temperature. Implications for the growth of Ba2YCu3O6+xcrystals are discussed.
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
authors.forename: Winnie
authors.initials: W
authors.lastname: Wong-Ng
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
authors.forename: Lawrence P
authors.initials: LP
authors.lastname: Cook
keywords: Ba2YCu3O6+x; liquid compositions; liquid immiscibility; phase equilibria; primary phase field; superconductors