Structural, electronic and magnetic properties of η-carbides M3W3C (M = Ti, V, Cr, Mn, Fe, Co, Ni)

• η-carbides M3W3C are stable for all 3d transition metals M.
• η-carbides should be more ductile than the typical binary carbides.
• nonmagnetic, ferromagnetic or antiferromagnetic state depending on 3d M.

First-principles calculations have been performed to study the structural, electronic and magnetic properties of η-carbides M3W3C depending on the type of 3d transition metal (TM). The mechanical properties, such as elastic moduli, mechanical stability and ductility as well as formation enthalpy, were predicted and compared with those for binary MxCy carbides. We find that the bulk, shear and Young’s modules have parabolic dependences on 3d TM with their maximum values for Fe3W3C. As follows from the elastic constants and moduli, all η-carbides should be more ductile than typical binary carbides with strong covalent M-C bonds. We predict M3W3C to be stable and discuss their precipitation sequences in comparison with binary carbides MC, M3C, M6C, M7C3, M5C2 and M23C6. Depending on the 3d TM, the ternary M3W3C carbides demonstrate a variety of magnetic structures which may be nonmagnetic or may consist of ferromagnetic tetrahedra, which are coupled ferromagnetically or antiferromagnetically.

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