On energetics of allotrope transformations in transition-metal diborides via plane-by-plane shearing

Abstract

Transition metal diborides crystallise in the $\alpha$, $\gamma$, or $\omega$ type structure, in which pure transition metal layers alternate with pure boron layers stacked along the hexagonal [0001] axis. Here we view the prototypes as different stackings of the transition metal planes and suppose they can transform from one into another by a displacive transformation. Employing first-principles calculations, we simulate sliding of individual planes in the group IV-VII transition metal diborides along a transformation pathway connecting the $\alpha$, $\gamma$, and $\omega$ structure. Chemistry-related trends are predicted in terms of energetic and structural changes along a transformation pathway, together with the mechanical and dynamical stability of the different stackings. Our results suggest that MnB${}_2$ and MoB${}_2$ possess the overall lowest sliding barriers among the investigated TMB${}_2$s. Furthermore, we discuss trends in strength and ductility indicators, including Young's modulus or Cauchy pressure, derived from elastic constants.

12 pages, 6 figures, accepted for publication in Vacuum, before proof

References in corpus (2)

• Necessary and Sufficient Elastic Stability Conditions in Various Crystal Systems
• Review of Transition-Metal Diboride Thin Films

Cited by in corpus (3)

• Machine-learning potentials for nanoscale simulations of deformation and fracture: example of TiB${}_2$ ceramic
• Phase stability and mechanical property trends for MAB phases by high-throughput ab initio calculations
• Machine-Learning Potentials Predict Orientation- and Mode-Dependent Fracture in Refractory Diborides