Ternary Carbide Phases Formed by Scandium-Group Elements with Aluminum and Carbon

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Abstract
A new group of ternary carbide phases which are formed by combination of an element of the scandium group (which is taken to include the rare-earth elements) with aluminum and carbon has been found. These phases are related to the series of T3BCx compounds discovered by Stadelmaier (T for a transition element and B for a B subgroup element). Atomic size effects are discussed which show that T3BCx phases behave in a manner similar to many ordered binary phases of AB3 stoichiometry. There is a readjustment in size of the various metallic components which results in effective radii compatible with cubic close packing. An anomaly which appears when the observed lattice parameters of T3BCx are related to the Goldschmidt radii of the component atoms is discussed in this light. Measurements of the intensities of X-ray diffraction peaks are used to show that the carbon atom in these phases occupies the octahedral hole in the center of a Cu3Au-type unit cell. This position is maintained in alloys which contain varying amounts of carbon.