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

• Published in: Vacuum Vol. 215; p. 112329
• Main Authors: Leiner, Thomas, Koutná, Nikola, Janovec, Jozef, Zelený, Martin, Mayrhofer, Paul H., Holec, David
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-09-2023
• Subjects: Ab initio calculations; Phase stability; Shear; Stacking sequence; Transition metal diborides; Phase stability; Shear; Ab initio calculations; Stacking sequence; Transition metal diborides
• ISSN: 0042-207X; 1879-2715; 1879-2715
• DOI: 10.1016/j.vacuum.2023.112329

Transition metal diborides crystallize in the α, γ, or ω 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 α, γ, and ω 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 MnB2 and MoB2 possess the overall lowest sliding barriers among the investigated TMB2s. Furthermore, we discuss trends in strength and ductility indicators, including Young’s modulus or Cauchy pressure, derived from elastic constants.
•Energy landscape of different stackings for group IV to VII transitionmetal diborides.•Dynamical instability of group VI and VII transitionmetal diborides in the α-stacking•Trends in the energy barriers of transitionmetal diborides and the puckering of the boron planes.•Electronic structure analysis explaining the structures of transitionmetal diborides.