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Instabilities in diamond under high shear stress
1Department of Physics, University of Texas, Austin, Texas 78712 and Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, CP 702, 30123-970, Belo Horizonte, MG, Brazil.
Physical Review Letters
|December 2, 2000
Summary
Diamond can become unstable under high shear stress, forming graphitelike structures. This instability is anisotropic, meaning stress direction significantly alters the outcome and required stress levels.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Computational Materials Science
Background:
- Diamond, known for its extreme hardness and stability, is a crucial material in various technological applications.
- Understanding its behavior under extreme conditions, such as high shear stress, is vital for predicting its performance and potential failure modes.
Purpose of the Study:
- To investigate lattice instabilities in diamond induced by high shear stresses using first-principles calculations.
- To determine the critical shear stress levels at which these instabilities occur and the resulting structural transformations.
- To explore the anisotropic nature of this phenomenon and the influence of stress direction and additional compressive forces.
Main Methods:
- Employing first-principles calculations to simulate the response of the diamond lattice to applied shear stresses.
- Analyzing the resulting structural changes, including bond breaking and the formation of layered graphitelike structures.
- Investigating the effect of reversing shear force direction and applying additional compressive stress along the (111) direction.
Main Results:
- A lattice instability leading to graphitelike layered structures was observed at shear stresses as low as 95 GPa.
- The instability was found to be highly anisotropic; reversing shear force direction altered the critical stress by up to 80 GPa and changed the orientation of the graphitelike structures.
- An additional compressive stress of 50 GPa along the (111) direction did not suppress the shear-induced instability.
Conclusions:
- Diamond can exhibit significant lattice instabilities under high shear stress, transforming into graphitelike structures.
- The mechanical response of diamond to shear stress is highly anisotropic, with profound implications for its structural integrity under varying load conditions.
- The findings highlight the complex behavior of diamond under extreme mechanical loads and suggest limitations in its stability under specific shear stress regimes.