Pressure effect on the structural properties of amorphous Ag during isothermal annealing F.A. Celik * , S. Kazanc, A.K. Yildiz, S. Ozgen Firat University, Faculty of Arts and Sciences, Physics Department, 23119 Elazıg, Turkey article info Article history: Received 30 January 2007 Received in revised form 20 February 2008 Accepted 11 March 2008 Available online 22 April 2008 Keywords: E. Molecular dynamics E. Embedded atom method C. Solidification B. Local order C. Nucleation abstract In this study, using molecular dynamics (MD) simulations we investigate the effect of pressure on the transformation from amorphous structure to crystalline structure during isothermal annealing of silver (Ag) model system with 2048 atoms. The structural development and phase transformation are analysed based on the variations of the radial distribution function, the bond-orientational order parameters and atomic configurations. In particular, in order to distinguish the local structures and number of clusters in the system the local structure of the system has been analysed from the bond-orientational order parameters. The crystal nucleation in amorphous phase, the growth of crystal nucleus and the formation of stable crystal phase during the crystallization process are also investigated for the model system. The simulation results showed that the applied pressure on the system caused further transformation from amorphous state to stable crystal phase during the crystallization process and also transformations from HCP/DHCP-like to FCC-like local structures. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction In the last few decades, there has been considerable attention on amorphous solids due to their interesting physical behaviour and applications in many fields. Amorphous solids are in a thermody- namically unstable state and crystallize into one or more unstable polycrystalline phases when they are subjected to heat treatments. It is known that atomic transport plays an important role in the liquid and amorphous states, and thus atomic clusters provide a bridge between atoms and molecules and bulk materials [1–3]. It is also known that crystallization process is, in general, the transformation from the liquid or amorphous state to solid state occurring in two stages as nucleation and crystal growth. In recent years, although the crystallization processes have attracted increasing research and scientific interest, there has been no enough work done on the study of crystallization process of amorphous alloys owing to the complexity of the process during isothermal annealing [4,5]. It is true that the experimental study is very difficult since the phase transition and nucleation are micro- scopic dynamics processes. On the other hand, it is appreciated that molecular dynamics (MD) simulation is a very useful tool in materials research and has been widely used in studying the crystallization and glass formation processes of materials during rapid solidification [6–8]. Moreover, in MD simulation studies calculation of bond- orientational order parameters has also been useful method to determine the local symmetric properties of cluster in liquid or amorphous systems [9–11]. For example, one of the earliest interesting studies was done by Steinhardt et al. [11] to calculate bond-orientational order in simulations of supercooled liquids and models of metallic glasses. Then, it has been used to determine the degree of crystalline and icosahedral order during melting and nucleation, and the local orientational symmetrical features of the clusters in liquid or amorphous metals [8,12,13]. In this study, we investigate the effect of pressure on the structural properties, especially FCC- and HCP/DHCP-like struc- tures, of Ag during transformation from amorphous state to crystalline state using MD simulations based on Sutton–Chen [14,15] (SC) EAM. The properties of cluster structures in amorphous and crystal phases of Ag have, in particular, been analysed with the local and global bond-orientational order parameters, and also the structure of the obtained solid and amorphous phases is analysed using RDF curves. In addition, atomic configuration the crystalli- zation process of amorphous model system during annealing is shown and illustrated. 2. Simulation and application process Let us first introduce briefly the inter-atomic potential which plays an important role in MD calculations, and also the EAM ap- plications on the liquid and amorphous phases of metallic systems * Corresponding author. Tel.: þ90 0424 2370000; fax: þ90 0424 2330062. E-mail address: facelik@firat.edu.tr (F.A. Celik). Contents lists available at ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet 0966-9795/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2008.03.002 Intermetallics 16 (2008) 793–800