Melting Investigation of the System BaF₂-BaO-½Y₂O₃-CuO_x-H₂O

Journal Article · Sat Jan 01 04:00:00 EST 2005 · Superconductor Science & Technology

DOI:https://doi.org/10.1088/0953-2048/18/4/012· OSTI ID:1003056

Wong-Ng, W. ^[1]; Cook, L. P. ^[1]; Suh, J. ^[1]; Levin, I. ^[1]; Feenstra, Roeland ^[2]

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1. National Institute of Standards and Technology (NIST)
2. ORNL

In order to understand low-temperature melting during the 'BaF{sub 2} process', equilibria in the quaternary Ba, Y, Cu//O, F reciprocal system have been investigated using a compositional model which can be represented as a trigonal prism. This prism is comprised of three tetrahedra: BaF{sub 2}-Y F{sub 3}-CuF{sub 2}-CuO{sub x}, BaF{sub 2}-Y F{sub 3}-1/2Y{sub 2}O{sub 3}-CuO{sub x}, and BaF{sub 2}-BaO-1/2Y{sub 2}O{sub 3}-CuO{sub x}. Systematic differential thermal analysis (DTA) studies of compositions spaced along compositional vectors extending from the fluoride end of the prism to the oxide end gave evidence of low-melting liquids (<600 {sup o}C) near the fluorine-rich region in the BaF{sub 2}-Y F{sub 3}-CuF{sub 2}-CuO{sub x} tetrahedron. In the intermediate BaF{sub 2}-Y F{sub 3}-1/2Y{sub 2}O{sub 3}-CuO{sub x} tetrahedron, a low-temperature DTA peak (550--570 {sup o}C) was also identified; this has been shown to be due to a reversible phase transformation in crystalline YOF. In the oxide-rich BaF{sub 2}-BaO-1/2Y{sub 2}O{sub 3}-CuO{sub x} tetrahedron, where, in the presence of water vapor, the principal defluorination process is generally thought to occur, the lowest melting temperature observed was 815 {sup o}C at p{sub O{sub 2}} = 20 Pa and p{sub H{sub 2}O} = 2.1 kPa. However, published observations on films undergoing the BaF{sub 2} process have suggested the presence of an amorphous phase thought to be a liquid at {<=} 735 {sup o}C. Based on our results, the low-melting liquids reported in the literature do not appear to exist as a stable liquid phase in the BaF{sub 2}-BaO-1/2Y{sub 2}O{sub 3}-CuO{sub x}-H{sub 2}O system under the conditions of our experiments. Rather, the formation of low-melting liquid in Ba-Y-Cu-O-F films at {<=} 735 {sup o}C may require (a) relatively fluorine-rich compositions, (b) metastable melting, (c) formation of hydroxide- or hydroxyfluoride-based liquids, or (d) some combination thereof.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: OE USDOE - Office of Electric Transmission and Distribution
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1003056
• Journal Information: Superconductor Science & Technology, Journal Name: Superconductor Science & Technology Journal Issue: 4 Vol. 18; ISSN 0953-2048; ISSN 1361-6668
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AMORPHOUS STATE
BARIUM FLUORIDES
BARIUM OXIDES
COPPER FLUORIDES
DIFFERENTIAL THERMAL ANALYSIS
FILMS
FLUORIDES
FLUORINE
LIQUIDS
MELTING
MELTING POINTS
OXIDES
PHASE TRANSFORMATIONS
PRISMS
TEMPERATURE RANGE 0065-0273 K
VECTORS
WATER VAPOR
YTTRIUM OXIDES