First-principles prediction of low shear-strain resistance of Al3BC3:: A metal borocarbide containing short linear BC2 units

The elastic stiffness and shear deformation mode of Al3BC3, a metal borocarbide containing linear C-B-C units, are studied based on the first-principles total energy calculations. The predominant effect of C-B-C units on mechanical properties is reported by leading to low shear modulus. The low shear-strain resistance originates from the deformation mode as follows: the rigid linear C-B-C units tilt with respect to the c direction easily, and the corner-sharing Al5C bipyramid slabs simultaneously slide along the basal plane with low resistance. The proposed deformation mode may be universal for the ternary metal borocarbides family containing short linear C-B-C units. (c) 2006 American Institute of Physics.