Structural properties of simulated liquid and amorphous TiO₂

Abstract

Structural properties of liquid and amorphous TiO 2 have been studied in a model containing 3000 particles under periodic boundary conditions with the pairwise interatomic potentials proposed by Matsui and Akaogi. Models have been obtained by cooling from the melt via molecular dynamics (MD) simulation. Structural properties of an amorphous model obtained at 350 K have been analyzed in details through the partial radial distribution functions (PRDFs), coordination number distributions, bond-angle distributions and interatomic distances. Calculations show that calculated data agree well with the experimental ones. The evolution of structure upon cooling from the melt was observed and discussed. Calculations show that amorphous TiO 2 has a distorted octahedral network structure with the mean coordination number

Structure of molten titanium dioxide

“…This is clear, for example, from the strong dependence of n TiO on density in models of liquid and amorphous TiO 2 [44,45,59,60], and from the following discussion sections V. B -V. D. The advantage of models capable of predicting density, such as those used here, is therefore significant.…”

“…The structure and properties thus derived are therefore more pertinent to the high pressure liquid, where both density and coordination numbers would be higher. With the slight modifications made in the present work to the Teter potentials, we were able to obtain the expected density (based on [39]) at 2250 K, and using these potentials, we estimate that the high liquid density of 3.80 g cm -3 used by Hoang [44,45] corresponds to a pressure of 4.8 GPa (note that the model pressure using the MA potentials would be much higher: 65 GPa at 2250 K and 3.21 g cm -3 ). Both the modified Teter potentials, and those of this work, allow for the prediction of the density ρ(T) over a wide range of temperatures, over much of the experimentally stable liquid region, and through supercooling to form glassy TiO 2 .…”

“…Many interatomic potential parameterizations for titanium-oxygen systems exist in the literature, and we test here only the most recent or relevant. The only published simulations of liquid TiO 2 were made by Hoang [44,45], using the potentials of Matsui and Akaogi (MA) [46], which were those recommended after a review, by Collins et al [47], of the existing potentials at the time (1996). We also assess the more recent potentials of Pedone et al [48] (Pedone hereafter) and the rigid ion potentials of Teter [49], the latter of which are unpublished, but have been used extensively in the literature, particularly for the simulation of silicate glasses [49,50] and melts [51,52] …”

“…The structure of liquid TiO 2 has previously been simulated by Hoang [44,45] using MD and the potentials of Matsui & Akaogi (MA) [46]. These were however conducted at fixed densities, independent of temperature, with the lowest liquid density used, 3.80 g cm -3 , corresponding to that of dense amorphous TiO 2 films [17], and much higher than the measured values [39] for the liquid.…”

On the microstructure of thin films grown by an isotropically directed deposition flux

“…This imposes an important constrain in our model, as the structure of amorphous TiO 2 is not cubic but mainly made of deformed octahedra, with average distances between Ti atoms between 3 and 4 Å. 24 Conversely, by knowing the typical distances in the material we can estimate the value of ⌬: we approximate ⌬ as the actual average distance between two Ti atoms in the amorphous network, i.e., ⌬ ϳ 3.5 Å. In the MC model we have not introduced neither surface diffusion nor desorption mechanisms, due to the low temperature of the film during growth.…”