Microstructures and theoretical bulk modulus of layered ternary tantalum aluminum carbides

Direct atomic resolution observations of the layered stacking characteristics of TaCx slabs and Al atomic planes in ternary Ta-Al-C carbides were achieved. Layered ternary Ta-Al-C compounds have diverse structures. A previously unknown Ta6AlC5 carbide, as well as intergrown Ta2AlC-Ta4AlC3 and Ta4AlC3-Ta6AlC5 structures were identified. Theoretical lattice parameters and bulk modulus of Ta2AlC, Ta3AlC2, Ta4AlC3, and Ta6AlC5 are presented. Furthermore, the Ta-C bonds are much stronger than the Ta-Al bonds in ternary Ta-Al-C carbides, which accounts for the enhancement of bulk modulus with increasing Ta-C layers.