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Published March 1, 2005 | Published
Journal Article Open

Hard superconducting nitrides


Detailed study of the equation of state, elasticity, and hardness of selected superconducting transition-metal nitrides reveals interesting correlations among their physical properties. Both the bulk modulus and Vickers hardness are found to decrease with increasing zero-pressure volume in NbN, HfN, and ZrN. The computed elastic constants from first principles satisfy c(11) > c(12) > c(44) for NbN, but c(11) > c(44) > c(12) for HfN and ZrN, which are in good agreement with the neutron scattering data. The cubic delta-NbN superconducting phase possesses a bulk modulus of 348 GPa, comparable to that of cubic boron nitride, and a Vickers hardness of 20 GPa, which is close to sapphire. Theoretical calculations for NbN show that all elastic moduli increase monotonically with increasing pressure. These results suggest technological applications of such materials in extreme environments.

Additional Information

© 2005 by the National Academy of Sciences. Contributed by Russell J. Hemley, January 7, 2005. Published online before print February 22, 2005, 10.1073/pnas.0500174102 Work at the Carnegie Institution was supported by U.S. Department of Energy Grant DEFG02-02ER4595, Office of Naval Research Grant N000140210506, the Department of Energy/Office of Basic Energy Sciences, Department of Energy/National Nuclear Security Administration, Carnegie/Department of Energy Alliance Center Grant DE-FC03-03N00144, the National Aeronautics and Space Administration, the National Science Foundation, and the W. M. Keck Foundation. Work at the Los Alamos National Laboratory was performed under the auspices of the Department of Energy. The High-Pressure Collaborative Access Team is a collaboration involving the Carnegie Institution of Washington, Lawrence Livermore National Laboratory, the University of Hawaii, the University of Nevada Las Vegas, and the Carnegie/Department of Energy Alliance Center at the Argonne National Laboratory.

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