Vacancy Hardening and Softening in Transition Metal Carbides and Nitrides

Seung-Hoon Jhi; Steven G. Louie; Marvin L. Cohen; Jisoon Ihm

doi:10.1103/PhysRevLett.86.3348

Vacancy Hardening and Softening in Transition Metal Carbides and Nitrides

Seung-Hoon Jhi, Steven G. Louie, Marvin L. Cohen, and Jisoon Ihm

Phys. Rev. Lett. 86, 3348 – Published 9 April 2001

Abstract

The effects of vacancies on mechanical properties of the transition metal carbides and nitrides are studied using the ab initio pseudopotential approach. Calculated shear elastic stiffness and electronic structures show that the vacancy produces entirely different effects on the mechanical strength of groups IVb nitrides and Vb carbides. It is found that the occupation of shear-unstable metallic $dd$ bonding states changes essentially in an opposite way for the carbides and nitrides in the presence of vacancies, resulting in different responses to shear stress. Our study provides an atomistic understanding of the anomaly in hardness for these substoichiometric materials.

Received 9 August 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.3348

Authors & Affiliations

Seung-Hoon Jhi^1,2, Steven G. Louie¹, Marvin L. Cohen¹, and Jisoon Ihm²

¹Department of Physics, University of California at Berkeley, and Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
²Department of Physics and Center for Theoretical Physics, Seoul National University, Seoul 151-742, Korea