Synthesis, crystal growth, and structure of Ta{sub 3}Al{sub 2}CoC-An ordered quarternary cubic {eta}-carbide and the first single crystal study of a {eta}-carbide

• Published in: Journal of solid state chemistry Vol. 181; no. 6
• Main Authors: Etzkorn, Johannes, Hillebrecht, Harald, Freiburger Materialforschungszentrum FMF, Stefan-Maier-Strasse 25, D-79104 Freiburg
• Format: Journal Article
• Language: English
• Published: United States 15.06.2008
• Subjects: CARBIDES; CERMETS; CRYSTAL GROWTH; CUBIC LATTICES; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MONOCRYSTALS; REFLECTION; SYNTHESIS; X-RAY DIFFRACTION
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2008.02.037

Single crystals of the new carbide Ta{sub 3}Al{sub 2}CoC were synthesised from metallic melt and characterized by XRD, EDX and WDX measurements. The crystal structure of Ta{sub 3}Al{sub 2}CoC was refined on the basis of single crystal data (cF112, Fd3-bar m, a=11.6153(13) A, Z=16, 169 reflections, 13 parameters, R{sub 1}(F)=0.0315, wR{sub 2}(F{sup 2})=0.0857). Ta{sub 3}Al{sub 2}CoC belongs to the great family of {eta}-carbides M{sub 3}M{sub 3}{sup '}C or M{sub 4}M{sub 2}{sup '}C which are important components for cermets. Its crystal structure is characterised by TaC{sub 6}-octahedra, which are connected to a three-dimensional net. Co and Al have icosahedral surroundings without contacts to C-atoms. All positions show full occupation. Ta{sub 3}Al{sub 2}CoC represents the first {eta}-carbide with a complete structure refinement on the basis of single crystal data. - Graphical abstract: Single crystals of the {eta}-carbide Ta{sub 3}Al{sub 2}CoC were grown from a Co-melt. Although {eta}-carbides are technologically very important as a constituent of cermets this is the first report on a single crystal study. The structure analysis of this quarternary variant shows the close similarity to the Ni{sub 2}Ti-structure as an ordering and filling variant. All sites are completely occupied and well ordered. Display Omitted.