Pressure-induced structural transition in amorphous TiO2 nanoparticles and in the bulk via molecular dynamics simulation

Abstract

The pressure-induced structural transition in amorphous TiO2 nanoparticles has been studied in a spherical model of different diameters of 2, 3 and 4 nm under non-periodic boundary conditions. We use the pairwise interatomic potentials proposed by Matsui and Akaogi. Models have been compressed from 3.8 g cm−3 up to very high density (i.e. high pressure) in order to investigate the pressure-induced structural changes. We found the change from the low-density amorphous (lda) form with ZTi–O ≈ 6.0 to the high-density amorphous (hda) one with ZTi–O ≈ 7.0 to be like those observed in practice. We found that the transition pressure is nanoparticle size dependent due to the surface effects. In order to compare and highlight the features of such transition in nanoparticles, we also present the results for the same transition in the amorphous TiO2 models containing 3000 atoms under periodic boundary conditions, which could be considered as bulk counterparts. Structural properties of nanoparticles at 700 K have been analysed in detail through the partial radial distribution functions, interatomic distances, coordination number and bond-angle distributions. Moreover, we also show the radial density profile in nanoparticles.