Strained structure of differently prepared amorphous TiO 2 nanoparticle: Molecular dynamics study
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Matusi–Akaogi force field is used in molecular dynamics simulations to generate three samples of amorphous TiO2 of 3-nm size under different heating and quenching rates. The averaged pair correlation functions, coordination numbers, bond lengths, bond angles, and dihedral angles are calculated at 315 K. It is found that overcoordinated Ti and O atoms are in the core region, 6- and 3-fold coordinated Ti and O atoms are in the central part, and undercoordinated Ti and O atoms are in the vicinity of the surface. The correlations are significant up to 10 Å and vanish at the particle size. The calculated averaged bond lengths for short-range interparticle correlations agree with the experimental data. The discrete bond angles and dihedral angles of crystalline sphere get distributed over complete range in the amorphous phase and closer strained atomic network is predicted. The relative variance in the atomic arrangements in three samples is within 4%.
I. INTRODUCTION
Nanosized titanium dioxide has been intensively investigated by experiments and computer simulations for its technological importance.1 Ye et al.2 analyzed the characteristics of nanocrystalline brookite-based TiO2, using thermodifferential and x-ray diffraction techniques. Petkov et al.3 did electron microscopy of nanophase amorphous-layered TiO2 produced by sputtering and sol– gel dip coating methods. Zhang et al.4 measured microRaman spectra of nanosized TiO2 powder prepared by vapor hydrolysis. Ahonen et al.5 observed that anatase synthesized in air transformed to rutile at 973 K, whereas anatase synthesized in nitrogen persisted up to 1173 K, and phase transformation is also affected by the interface nucleation and the presence of impurities.6–8 Wang et al.9 and Nakade et al.10 synthesized rutile and anatase TiO2 by chemical solution method, and Wu et al.11 did sol-hydrothermal synthesis to produce nanoparticles of TiO2. Aruna et al.12 and Zhang and Banfield13 produced rutile titania particles by autoclaving process. Ranade et al.14 studied energetics of nanocrystalline TiO2 prepared by mixing the solutions of TiCl3 and NH4OH, whereas Wei et al.15 studied magnetism of TiO and TiO2 nanoclusters prepared by oxidation of Ti clusters. These experimental findings suggest that nanosized TiO2 can exist in anatase, rutile, and brookite structures and these become amorphous below 673 K.4,5 The exhibited refractive indices, chemical and photochemical reactivities also depend upon the fabrication conditions, heat treatment, and size of the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.237 2604
J. Mater. Res., Vol. 26, No. 20, Oct 28, 2011
http://journals.cambridge.org
Downloaded: 06 Oct 2015
nanoparticles as the atomic network in differently prepared samples may not be the same. Molecular dynamics (MD) simulations have also been carried out using Matsui and Akaogi16 (MA) force field to study collision and fusion processes.17 The temperaturedependent thermodynamical properties18,19 of crystalline TiO2 nanoparticle
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