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- Title
Reduction of the bulk modulus at high pressure in CrN.
- Authors
Rivadulla, Francisco; Bañobre-López, Manuel; Quintela, Camilo X.; Piñeiro, Alberto; Pardo, Victor; Baldomir, Daniel; López-Quintela, Manuel Arturo; Rivas, José; Ramos, Carlos A.; Salva, Horacio; Jian-Shi Zhou; Goodenough, John B.
- Abstract
Nitride coatings are increasingly demanded in the cutting- and machining-tool industry owing to their hardness, thermal stability and resistance to corrosion. These properties derive from strongly covalent bonds; understanding the bonding is a requirement for the design of superhard materials with improved capabilities. Here, we report a pressure-induced cubic-to-orthorhombic transition at ≈1 GPa in CrN. High-pressure X-ray diffraction and ab initio calculations show an unexpected reduction of the bulk modulus, K0, of about 25% in the high-pressure (lower volume) phase. Our combined theoretical and experimental approach shows that this effect is the result of a large exchange striction due to the approach of the localized Cr:t3 electrons to becoming molecular-orbital electrons in Cr–Cr bonds. The softening of CrN under pressure is a manifestation of a strong competition between different types of chemical bond that are found at a crossover from a localized to a molecular-orbital electronic transition.
- Subjects
NITRIDES; PROTECTIVE coatings; COATING processes; SURFACE hardening; SURFACES (Technology); CHEMICAL bonds
- Publication
Nature Materials, 2009, Vol 8, Issue 12, p947
- ISSN
1476-1122
- Publication type
Article
- DOI
10.1038/nmat2549