Powder neutron diffraction of. alpha. -UB sub 2 C (. alpha. -UB sub 2 C-type)

Journal Article · Fri Feb 01 04:00:00 EST 1991 · Journal of Solid State Chemistry; (USA)

DOI:https://doi.org/10.1016/0022-4596(91)90144-7· OSTI ID:5491836

Rogl, P ^[1]; Fischer, P ^[2]

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1. Universitaet Wien (Austria)
2. Eidgenoessische Technische, Villigen (Switzerland)

The crystal structure of {alpha}-UB{sub 2}C (low temperature modification below T = 1675(25){degree}C) was determined from powder X-ray data (RT) and powder neutron diffraction data (at 29 K) employing the Rietveld-Young-Wiles profile analysis method. {alpha}-UB{sub 2}C crystallizes in the orthorhombic space group Pmma with a = 0.60338(3), b = 0.35177(2), c = 0.41067(2)nm, V = 0.0872 nm{sup 3}, Z = 2. The residuals of the neutron refinement were R{sub I} = 0.032 and R{sub F} = 0.043. The crystal structure of {alpha}-UB{sub 2}C is a new structure type where planar nonregular 6{sup 3}-U-metal layers alternate with planar nonmetal layers of the type (B{sub 6}C{sub 2}){sup 3}. Boron atoms are in a typical triangular prismatic metal surrounding with a tetrakaidekahedral coordination B(U{sub 6}B{sub 2}C{sub 1}), whereas carbon atoms occupy the center points of rectangular bipyramids C(U{sub 4}B{sub 2}). The crystal structure of {alpha}-UB{sub 2}C derives from the high temperature modification {beta}-UB{sub 2}C (ThB{sub 2}C-type, R{bar 3}m), which reveals a similar stacking of slightly puckered metal layers 6{sup 3}, alternating with planar layers B{sub 6}{center dot}(B{sub 6}C{sub 3}){sup 2}. The phase transition from {beta}-UB{sub 2}C to {alpha}-UB{sub 2}C is thus essentially generated by carbon diffusion within the {sub {infinity}}{sup 2} B{sub 6}{center dot}(B{sub 6}C{sub 3}){sup 2} layers to form {sub {infinity}}{sup 2} (B{sub 6}C{sub 2}){sup 3} layers.

• OSTI ID: 5491836
• Journal Information: Journal of Solid State Chemistry; (USA), Journal Name: Journal of Solid State Chemistry; (USA) Vol. 90:2; ISSN 0022-4596; ISSN JSSCB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ACTINIDE COMPOUNDS
BORON CARBIDES
BORON COMPOUNDS
CARBIDES
CARBON COMPOUNDS
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
DATA
DATA ANALYSIS
DIFFRACTION
EXPERIMENTAL DATA
INFORMATION
NEUTRON DIFFRACTION
NUMERICAL DATA
ORTHORHOMBIC LATTICES
PHASE TRANSFORMATIONS
SCATTERING
URANIUM CARBIDES
URANIUM COMPOUNDS