Synthesis, crystal growth, and structure of Ta3Al2CoC—An ordered quarternary cubic η-carbide and the first single crystal study of a η-carbide

Single crystals of the new carbide Ta3Al2CoC were synthesised from metallic melt and characterized by XRD, EDX and WDX measurements. The crystal structure of Ta3Al2CoC was refined on the basis of single crystal data (cF112, Fd3¯m, a=11.6153(13) Å, Z=16, 169 reflections, 13 parameters, R1(F)=0.0315, wR2(F2)=0.0857). Ta3Al2CoC belongs to the great family of η-carbides M3M3′C or M4M2′C which are important components for cermets. Its crystal structure is characterised by TaC6-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. Ta3Al2CoC represents the first η-carbide with a complete structure refinement on the basis of single crystal data.

Graphical abstractSingle crystals of the η-carbide Ta3Al2CoC were grown from a Co-melt. Although η-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 Ni2Ti-structure as an ordering and filling variant. All sites are completely occupied and well ordered.Figure optionsDownload full-size imageDownload as PowerPoint slide