The crystal structures of Zr{sub 3}Al{sub 3}C{sub 5}, ScAl{sub 3}C{sub 3}, and UAl{sub 3}C{sub 3} and their relation to the structures of U{sub 2}Al{sub 3}C{sub 4} and Al{sub 4}C{sub 3}
- Univ. Muenster (Germany). Anorganisch-Chemisches Inst.
Single crystals of Zr{sub 3}Al{sub 3}C{sub 5} -- a carbide previously reported with the formula ZrAlC{sub 2{minus}x} -- were isolated from a sample prepared by reaction of ZrC with an excess of aluminum. The carbides ScAl{sub 3}C{sub 3} and UAl{sub 3}C{sub 3} were synthesized from the elemental components by arc-melting. The crystal structures of these three compounds were redetermined from four-circle X-ray diffractometer data. In the original structure determination of ZrAlC{sub 2{minus}x}, the metal positions were found to form close-packed layers in the space group P6{sub 3}/mmc, while the carbon atoms were assumed to occupy 5/6 of the octahedral voids at random. The present structure determination in the space group P6{sub 3}/mc (R = 0.024 for 519 structure factors and 23 variable parameters) shows that all carbon positions are fully occupied and one has a trigonal bipyramidal aluminum coordination. The structures of ScAl{sub 3}C{sub 3} and UAl{sub 3}C{sub 3} also have originally been determined in the space group P6{sub 3}/mmc. In all of these structures the metal atoms are arranged in close-packed layers and together with the previously reported structure of U{sub 2}Al{sub 3}C{sub 4} they form a homologous series with the general formula T{sub 1+n}Al{sub 3}C{sub 3+n}, where n = 0, 1, 2 for ScAl{sub 3}O{sub 3}, U{sub 2}Al{sub 3}C{sub 4}, and Zr{sub 3}Al{sub 3}C{sub 5}, respectively. The packing of the metal atoms is represented by the Zhdanov symbols (4){sub 2}, (5){sub 2}, and (6){sub 2}. The arrangement of the aluminum atoms is very similar to that of the binary carbide Al{sub 4}C{sub 3}, while the other metal atoms form a cubic stacking sequence, as it is found in the binary carbides TC with NaCl type structure.
- OSTI ID:
- 305383
- Journal Information:
- Journal of Solid State Chemistry, Vol. 140, Issue 2; Other Information: PBD: 1 Nov 1998
- Country of Publication:
- United States
- Language:
- English
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