Met. Mater. Int., Vol. 16, No. 2 (2010), pp. 163~169 doi: 10.1007/s12540-010-0402-3 Published 26 April 2010 Effects of Temperature and Tilt Angle on the Grain Boundary Structure in Silicon Oxide: Molecular Dynamics Study Sae-Jin Kim 1,2 , Jung-Hae Choi 1, * , Seung-Cheol Lee 1 , and Chan Park 2 1 Computational Science Center, Korea Institute of Science and Technology, Seoul 130-650, Korea 2 School of Materials Science and Engineering, Seoul National University, Seoul 151-744, Korea (received date: 24 April 2009 / accepted date: 28 September 2009) Molecular Dynamic (MD) simulations on a crystalline and amorphous silicon oxide were performed by using modified-Born-Mayer-Huggins (modified-BMH) potential. Comparison of the lattice parameters and analyses of the RDF for five different bulk phases of silicon oxide showed that the modified-BMH potential was properly able to describe crystalline phases, as well as the amorphous phase. When a polycrystalline model system that was composed of two β-cristobalite grains with a tilt grain boundary was annealed, an amorphous- like grain boundary region formed. The thickness of the grain boundary region was practically identical, regardless of the annealing temperature within the MD calculation time, which showed a very early stage of grain boundary amorphization. The atomic distribution in the grain boundary region became more uniform as the annealing temperature increased due to the faster relaxation. On the other hand, the atomic configuration and the thickness of the grain boundary region hardly depended on the grain boundary tilt angle. Keywords: computer simulation, oxide, grain boundary, annealing, microstructure 1. INTRODUCTION Silicon oxide has been one of the most intensively studied materials due to its industrial importance and natural abun- dance [1]. The main concerns have been emphasized on the gate oxide of Si-based semiconductors. In addition, silicon oxide has been utilized for other applications, such as high- temperature sensors [2], resonators [2,3], coating layers [4], and low-electric fillers [5] due to the piezoelectric character- istics and high temperature stability. Silicon oxide has various polymorphs [6], and is one of the most well-known glass formers [7], that show short range atomic structures, such as bond length and bond angle, as not being different in each phase [6]. However, the different long range orders in different phases can result in different prop- erties. This implies that an understanding of the atomic structure is important in controlling the properties of silicon oxide. On the other hand, thin intergranular films have been commonly observed in grain boundaries [8-14] and they have been frequently incorporated with a small amount of impurities in ceramic materials [8-10]. However, observations of the initial formation of grain boundaries in atomic simula- tions are possible, which is beneficial in understanding the structure of grain boundaries in pure ceramic materials. In order to examine the atomic structures, where the long- range interactions are involved, large scale atomic simula- tions were used and have been considered to be effective. Molecular Dynamics (MD) is one of the atomic simulation techniques in the field of nanotechnology. It provides physi- cal insights for understanding various atomic phenomena which cannot be approached by conventional experiments. For MD simulations, empirical interatomic potentials are practically valuable for studying both static and dynamic properties, even at non-zero temperature. In addition, the validity of the empirical potential is one of the most important issues in predicting the atomic behavior by using the MD technique. There have been many studies on developing the potential for silicon oxide based on empirical methods and ab-initio calculations [15-27]. Recently, advanced force fields for sili- con oxide were reported that considered the bond order parameter [26,27]. The Modified-Born-Mayer-Huggins (modi- fied-BMH) potential used in this study is one of the classical empirical potential based on the potential proposed by Vash- ista et al. [15], which took into account the coulombic force and additional Van der Waals force. Note that the modified- BMH potential was originally developed to characterize the amorphous silicon oxide [16,17] by considering the angle *Corresponding author: choijh@kist.re.kr KIM and Springer