Elastic constants of beta-eucryptite: A density functional theory study

Abstract

The five independent elastic constants of hexagonal $\beta$-eucryptite have been determined using density functional theory (DFT) 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 the direct measurements based on a three-terminal technique. The calculated compressibility parallel to the c-axis was found to positive as opposed to the negative value obtained by direct measurements. We have demonstrated that ${\chi }_c$ must be positive and discussed the implications of a positive ${\chi }_c$ in the context of explaining the negative bulk thermal expansion of $\beta$-eucryptite.

3 eps figures, submitted for publication

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