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Materials science

The hard problem of carbonitrides

Nature volume 399, pages 108–109 (1999)Cite this article

‘Materials by design’ is the goal of theorists who are developing a fundamental understanding of the macroscopic properties of materials from a microscopic, atomistic point of view. In a paper on page 132of this issue, Jhi et al.1 move us towards this goal by relating the hardness properties of carbonitrides — compounds containing carbon or nitrogen, together with a transition metal2 — to fundamental aspects of the material's electronic structure such as the electronic energy bands, or the charge density and chemical bonding. They show that the elastic properties of the carbonitrides, which relate to their hardness, can be explained by the filling of electron states depending on whether the underlying lattice is occupied by transition-metal or carbon and nitrogen atoms, or by vacancies. The authors have used state-of-the-art theoretical and computational methods to reach this conclusion from first principles, without recourse to tweaking the theoretical parameters with experimental data. An understanding of the hardness of the carbonitrides does not seem so hard any longer.

Carbonitrides (such as TiC or NbN) often form in the simple NaCl crystal-lattice structure of ordinary table salt. The valence electron concentration, or number of electrons that are active in the bonding of these materials (there are eight such electrons in TiC, and ten in NbN) can be changed by forming alloy compounds with varying amounts of transition metal(s), carbon and nitrogen atoms, or vacancies. Such materials often have interesting properties ranging from superconductivity at relatively high temperatures3,4 (for example, T c > 17 K for NbN), to high melting temperatures, and to the extreme hardness (such as TiC, which has a relative hardness somewhere between that of aluminium oxide and diamond) that makes them important materials for cutting tools and related applications.

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References

  1. Jhi, S.-H., Ihm, J., Louie, S. G. & Cohen, M. L. Nature 399, 132–134 (1999).

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  2. Toth, L. E. Transition Metal Carbides and Nitrides (Academic, New York, 1971).

  3. Klein, B. M. & Papaconstanttopoulos, D. A. Phys. Rev. Lett. 32, 1193–1196 (1974).

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  4. Papaconstantopoulos, D. A., Pickett, W. E., Klein, B. M. & Boyer, L. L. Nature 308, 494–495 (1984).

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  5. Kohn, W. & Vashishta, P. in Theory of the Inhomogeneous Electron Gas (eds Lundqvist, S. & Marsh, N. H.) 79-147 (Plenum, New York, 1983).

  6. Singh, D. J. Planewaves, Pseudopotentials, and the LAPW Method (Kluwer, Boston, 1994).

  7. Zunger, A. in Statics and Dynamics of Alloy Phase Transitions NATO ASI Series B Vol. 319 (eds Turchi, P. E. A. & Gonis, A.) 361-419 (Plenum, New York, 1994).

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  1. Department of Physics, University of California, One Shields Avenue, Davis, 95616, California, USA

    Barry M. Klein

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  1. Barry M. Klein
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Klein, B. The hard problem of carbonitrides. Nature 399, 108–109 (1999). https://doi.org/10.1038/20084

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