A Combined Ab Initio and Bond-Order Potentials Study of Cohesion in Iridium

The extremely high melting point and excellent resistance to oxidation and corrosion offered by iridium suggest numerous applications of this transition metal in static components at high temperatures and in aggressive environments. However, the mechanical and physical properties of f.c.c. Ir exhibit numerous anomalies when compared to other metals that crystallize in the f.c.c. structure. Notable examples include a negative Cauchy pressure, 1/2 (C12 – C44), brittle transgranular cleavage after a period of plastic flow even in pure single crystals and anomalous [zeta zeta 0] branches in the phonon spectra. Atomistic studies of extended defects are needed to elucidate the origin of anomalous mechanical properties, such as brittleness. For this purpose we developed a Bond-Order Potential (BOP), an O(N) tight-binding formalism, employing physically transparent parameterizations that use experimental and ab initio data, generated in this study using the Full Potential Augmented Plane Wave plus Local Orbitals (APW+lo) method. The constructed BOP reproduces then both equilibrium as well as a variety of non-equilibrium properties of Ir and represents an excellent description of cohesion in f.c.c. Ir. This description of interatomic interactions is imminently suitable for studies of defects, such as dislocations and grain boundaries, that control plastic deformation and fracture. Comments Copyright Materials Research Society. Reprinted from Materials Research Society Proceedings, Symposium W : Multiscale Phenomena in Materials--Experiments and Modeling Related to Mechanical Behavior, Volume 779, 2003. Publisher URL: http://www.mrs.org/members/proceedings/spring2003/w/ This conference paper is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/7 A Combined Ab Initio and Bond-Order Potentials Study of Cohesion in Iridium Marc J. Cawkwell, Duc Nguyen-Manh, Vaclav Vitek and David G. Pettifor. Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104-6272, U.S.A. Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UNITED KINGDOM.