Determining Activation Volume for the Pressure-Induced Phase Transformation in β-Eucryptite Through Nanoindentation

beta-eucryptite (LiAlSiO4) has received widespread attention, both industrially and academically because of its low negative average coefficient of thermal expansion (CTE) and one dimensional Li-ion conductivity. It undergoes a reversible pressure-induced phase transformation at similar to 1 GPa to a metastable polymorph, e-eucryptite. In the present work, low load (similar to 30 mu N) nanoindentation tests were performed on polycrystalline and single crystal beta-eucryptite to characterize this phase transformation. Hundreds of tests at several loading rates revealed a rate-dependence, with higher loading rates suppressing the deviation from isotropic elastic behaviora signature of a thermally-activated process. The occurrence of reversible hysteretic loops in the load-displacement curves is consistent with a reversible process during nanoindentation, viz. the phase transformation. Calculations of the activation volume suggest that the nucleation event that is believed to mark the onset of the phase transformation is approximately the size of the silica and alumina tetrahedra comprising the beta-eucryptite structure. This study provides fundamental insights into the mechanism of pressure-induced phase transformation in beta-eucryptite.