Anisotropic thermal expansion of calcium dialuminate (CaAl4O7) simulated by molecular dynamics

The anisotropic thermal expansion behavior of CaAl4O7 was studied by molecular dynamics (MD) simulation in the temperature range from 298 to 700 K. The monoclinic crystal structure (space group C2/c) has been successfully reproduced by using a simple 2-body potential. The principal distortions (λ1, λ2, λ3) and the coefficients of linear thermal expansion (α1, α2, α3) along with the principal axes have been calculated from the temperature dependence of the unit-cell parameters, a, b, c, and β. The distortion λ3 was much smaller than the other two distortions for all the temperature range, which was partially consistent with the experimental work performed by Fukuda et al. The anisotropic thermal expansion behavior can be explained by the crystallographic geometry, i.e. directional difference in the packing density.