Microstructures and Theoretical Bulk Modulus of Layered Ternary Tantalum Aluminum Carbides

Direct atomic resolution observations of the layered stacking characteristics of TaC x 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 Ta 6 AlC 5 carbide, as well as intergrown Ta 2 AlC–Ta 4 AlC 3 and Ta 4 AlC 3 –Ta 6 AlC 5 structures were identified. Theoretical lattice parameters and bulk modulus of Ta 2 AlC, Ta 3 AlC 2 , Ta 4 AlC 3 , and Ta 6 AlC 5 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.