Article abstract
Nature Materials 8, 947 - 951 (2009)
Published online: 25 October 2009 | doi:10.1038/nmat2549
Subject Categories: Mechanical properties | Design synthesis and processing
Reduction of the bulk modulus at high pressure in CrN
Francisco Rivadulla1, Manuel Bañobre-López1, Camilo X. Quintela2, Alberto Piñeiro2,3, Victor Pardo2,3, Daniel Baldomir2,3, Manuel Arturo López-Quintela1, José Rivas2, Carlos A. Ramos4, Horacio Salva4, Jian-Shi Zhou5 & John B. Goodenough5
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.
- Physical-Chemistry Department, University of Santiago de Compostela, 15782-Santiago de Compostela, Spain
- Applied Physics Department, University of Santiago de Compostela, 15782-Santiago de Compostela, Spain
- Instituto de Investigaciones Tecnológicas, Universidad de Santiago de Compostela, E-15782, Santiago de Compostela, Spain
- Centro Atómico de Bariloche, 8400 San Carlos de Bariloche, Rio Negro, Argentina
- Texas Materials Institute, ETC 9.102, The University of Texas at Austin, Austin, Texas 78712, USA
Correspondence to: Francisco Rivadulla1 e-mail: f.rivadulla@usc.es
