Atomic structure of the (310) twin in niobium: Experimental determination and comparison with theoretical predictions

Abstract

The atomic structure of the (310) twin in Nb was predicted using interatomic potentials derived from the embedded atom method (EAM), Finnis-Sinclair theory (FS), and the model generalized pseudopotential theory (MGPT). The EAM and FS predicted structures with crystal translations which break mirror symmetry. The MGPT predicted one stable structure which possessed mirror symmetry. This defect was experimentally determined to have mirror symmetry. These findings emphasize that the angular dependent interactions modeled by the MGPT are important for determining defect structures in bcc transition metals. PACS numbers: 61.16.Bg, 61.72.MmAtomistic simulations which can model the interactions of many tens of thousands of atoms are increasingly used as a predictive tool and have the potential to play an important role in the overall understanding of the properties of the solid state [1], such as the atomic structure of defects [2], segregation [3l, and fracture [41. The present investigation seeks experimental distinction between several models of the interatomic interactions used in these types of calculations. In particular, the interest is to assess the differences among the embedded atom method (EAM) [5,6], Finnis-Sinclair theory (FS) [7], and the model generalized pseudopotential theory (MGPT) [8] for predicting the atomic structure of defects in body-centered-cubic (bcc) transition metals and whether the predictions correspond with experimental observations. The predictive power of the EAM and FS for face-centered noble metals is well established [2,9]. Defect structures in bcc transition metals may be less easily predicted due to the partial filling of the d bands which is expected to add an angular dependence to the interactions [10].The grain-boundary calculations studied here differ primarily by the absence or inclusion of angular dependent interactions. The EAM and FS potentials are both of the pair-functional form [10], where the energy contains a term which is a function of a simple pairwise sum over neighbors. They incorporate the trend that higher coordination implies longer, weaker bonds. However, they include no angular dependence of the atomic interactions. In contrast, the MGPT potentials incorporate three-and four-body interactions based on a model treatment of canonical d bands [8]. Only potentials which incorporate angular dependencies have been shown to predict the correct reconstruction of Mo and W (100) surfaces [11,12], while this is not possible with pairfunctional methods [13]. Grain boundaries are more similar to the bulk than surfaces, possessing comparable coordination, and should provide additional information on the importance of angular dependent interactions due to the different atomic arrangements. Other potential forms which incorporate angular dependent interactions are being pursued by a number of investigators [10,14,15], but, at present, little experimental data exist for grain-boundary structures in bcc transition metals [16,17].High-resolution transmission electron microscopy (...

Electronic Effects on Grain Boundary Structure in Bcc Metals

“…The results of the present study on Ta, when combined with previously reported results on Nb [8] and MO [9], reaffirms the predictive power of the MGPT derived potentials for modeling defect structures in the BCC metals.…”

“…The model of interatomic interactions with angular dependence that we use is the Model Generalized Psuedopotential Theory (MGPT) [5]. We have applied it to modeling the x5 (3 1 O)/[OO 1 ] symmetric tilt grain boundary (STGB) in niobium [8], molybdenum [9], and tantalum as a critical test of its accuracy. We report here on the results for Ta.…”

Imeall: A computational framework for the calculation of the atomistic properties of grain boundaries

“…[18,19] where classical potentials identify non-physical minimum energy grain boundary structures. The minimum energy structure identified by embedded atom potentials has a tendency to favour structures preserving the coordination number at the interface.…”

Ab-Initio Determination of the Atomic Structure of Symmetrical Tilt Grain Boundaries in BCC Transition Metals

“…The rapid development of computers enables such simulations to be carried out presently for systems with about i06 atoms on conventional workstations, and with up to i0 9 atoms and short-range interatomic interactions on massively parallel supercomputers. Examples of successful studies for materials include determinations of atomic arrangements along grain boundaries, of dislocation core structures, or of atomic structures and dynamical propagations of crack tips in metals, semiconductors and ionic crystals.…”