Determining the volume thermal expansion coefficient of TiO2 nanoparticle by molecular dynamics simulation

In the present work, molecular dynamics (MD) simulation was employed for determining the volume thermal expansion coefficient (VTEC) of rutile TiO2 nanoparticle and its inner crystalline core, between 300 and 1000 K. As compared to the previous studies, which have focused on the bulk TiO2, this work has paid special attention to the VTEC of TiO2 nanoparticle. A novel method was proposed to determine the VTEC of inner crystalline core of nanoparticle. The results revealed that the room temperature VTEC of rutile nanoparticle (35.80 K−1) was higher than that of both bulk rutile (23.54 K−1) and crystalline core of nanoparticle (22.15 K−1). The decrease in the average coordination number of titanium ion, within amorphous surface layer, with increasing temperature was found to be the reason of this observation. Furthermore, it was observed that the VTEC of both crystalline core of rutile nanoparticle and bulk rutile increases as the temperature increases, whereas this parameter decreases with temperature for rutile nanoparticle. This behavior was explained by the decrease in VTEC of amorphous surface layer of nanoparticle with increasing temperature.