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arXiv · 2301.12840

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

Thomas Leiner·Nikola Koutná·Jozef Janovec·Martin Zelený·Paul H. Mayrhofer·David Holec
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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.

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Thomas Leiner, Nikola Koutná, Jozef Janovec, Martin Zelený, Paul H. Mayrhofer, David Holec. 2023-01-30. On energetics of allotrope transformations in transition-metal diborides via plane-by-plane shearing. https://doi.org/10.1016/j.vacuum.2023.112329

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