Lithium diffusion in rutile structured titania

Lithium diffusion in rutile TiO2 has been investigated by means of molecular dynamics. Simulations were performed using a model that allows charge transfer among ions. The ionic charges were dynamically calculated each timestep via an extended Lagrangian method. An additional Nose-Hoover chain thermostat was used in order to keep the charges at low temperature, preventing thermal coupling between nuclear and charge degrees of freedom. The model yielded reasonable values for the ionic charges, in good agreement with quantum mechanical calculations for titanium and oxygen and somewhat smaller values for the lithium ions. The simulations show an expected one-dimensional diffusion along channels parallel to the [001] direction. Lithium diffusion occurs through jumps between octahedral sites located along these channels. The diffusion coefficient of lithium was measured for temperatures ranging from 300 to 900 K and concentrations up to 0.75 lithium/titanium atomic ratio. At room temperature, values of up to 1.1 x 10(-6) cm(2)/s were recorded for low concentrations. Results show that increasing the lithium concentration causes diffusion to slow significantly and to display anomalous, non-Arrhenian, behavior. (c) 2006 Elsevier B.V. All rights reserved.