Nonlinear deformation and elasticity of BCC refractory metals and alloys

Vishnu Raghuraman, Michael Widom, and Michael C. Gao
Phys. Rev. Materials 6, 053601 – Published 2 May 2022

Abstract

Application of isotropic pressure or uniaxial strain alters the elastic properties of materials; sufficiently large strains can drive structural transformations. Linear elasticity describes stability against infinitesimal strains, while nonlinear elasticity describes the response to finite deformations. It was previously shown that uniaxial strain along [100] drives refractory metals and alloys towards mechanical instabilities. These include an extensional instability, and a symmetry-breaking orthorhombic distortion caused by a Jahn-Teller-Peierls instability that splays the cubic lattice vectors. Here we analyze these transitions in depth. Eigenvalues and eigenvectors of the Wallace tensor identify and classify linear instabilities in the presence of strain. We show that both instabilities are discontinuous, leading to discrete jumps in the lattice parameters. We provide physical intuition for the instabilities by analyzing the changes in first-principles energy, stress, bond lengths, and angles upon application of strain. Electronic band structure calculations show differential occupation of bonding and antibonding orbitals, driven by the changing bond lengths and leading to the structural transformations. Strain thresholds for these instabilities depend on the valence electron count.

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  • Received 2 February 2022
  • Accepted 19 April 2022

DOI:https://doi.org/10.1103/PhysRevMaterials.6.053601

©2022 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Vishnu Raghuraman* and Michael Widom

  • Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA

Michael C. Gao

  • National Energy Technology Laboratory, Albany, Oregon 97321, USA

  • *Corresponding author: vishnura@andrew.cmu.edu

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Issue

Vol. 6, Iss. 5 — May 2022

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