Melting Investigation of the System BaF2-BaO-½Y2O3-CuOx-H2O
- National Institute of Standards and Technology (NIST)
- 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 Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- OE USDOE - Office of Electric Transmission and Distribution
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1003056
- Journal Information:
- Superconductor Science & Technology, Vol. 18, Issue 4; ISSN 0953--2048
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
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