Molecular dynamic simulation of the [N(C4H9)4]BF4 / (110) α-Al2O3 interface

The structure and transport properties of the pure salt [N4]BF4 and this salt located in the contact with the (110) surface of a-Al2O3 were studied using a MD computer simulation in order to reveal the effect of the salt/oxide interface on the structure and properties of the salt. The radial distribution functions of the ions and their mean square displacements were analyzed as a function of the temperature during the cooling of the salt. It was found that in all the cases anions are more mobile than cations. The molten phase of [N4]BF4 tends to crystallize at temperature 420 K which is close to the experimental melting point. The salt located in the [N4]BF4/(110)Al2O3 interface exhibits high values of anion self-diffusion coefficients which are higher by 1.2–2 orders of magnitude than in pure salt. This effect is likely to be caused by the formation of a layered atomic structure located within a characteristic thickness of 5 nm. Despite the structuring, the structure of the salt is amorphous, no crystallization-related effect is observed. The results of MD simulations agree with the experimental effect of the conductivity enhancement observed previously in [N4]BF4-Al2O3 nanocomposites.