Elastic constants of β-eucryptite studied by density functional theory

The five independent elastic constants of hexagonal beta-eucryptite have been determined using density functional theory total energy calculations. The calculated values agree well, to within 15%, with the experimental data. Using the calculated elastic constants, the linear compressibility of beta-eucryptite parallel to the c axis, chi(c), and perpendicular to it, chi(a), have been evaluated. These values are in close agreement to those obtained from experimentally known elastic constants, but are in contradiction to those obtained through direct measurements based on a three-terminal technique. The calculated compressibility parallel to the c axis was found to have a positive value rather than a negative one as obtained from the three-terminal technique. We demonstrate that chi(c) must be positive and discuss the implications of a positive chi(c) in the context of explaining the negative bulk thermal expansion of beta-eucryptite.