Authors: V.V. Hoang and H. Zung
Affilation: Institute of Technology, National University of HochiMinh City, Viet Nam
Pages: 328 - 331
Keywords: amorphous silica, amorphous nanoparticle, surface structure
Via Molecular Dynamics simulation we found the transition from low density to high density states in an amorphous SiO2 nanoparticle under compression from 2.20 g/cm3 to 5.35 g/cm3. Simulations were done in a spherical model containing 2214 atoms under non-periodic boundary conditions with interatomic potentials which have a weak Coulomb interaction and Morse type short-range interaction. Amorphous SiO2 nanoparticle at 2.20 g/cm3 has been obtained by cooling from the melt. However, unlike those observed in the bulk (i.e. it was found a clear transition from a tetrahedral to an octahedral network structure under compression over the same density range ) we found just the transition from a tetrahedral to a pentahedral network structure in nanoparticles, the mean coordination number for Si-O pair increases from 4.00 to 5.10 (i.e. SiO5 structural units have dominated fraction in high density model of 5.35 g/cm3, see more details in Fig. 1 and Table 1). This indicates surface effects on the pressure-induced phase transition in nanoscaled system. The changes in coordination number for different atomic pairs in the core and at surface of nanoparticles upon compression have been found and discussed (Table 2). Moreover, density dependence of surface energy and other thermodynamics quantities of nanoparticles has been found and presented.