  We report studies on the vibrational and elastic behavior of lithium oxide,
Li2O around its superionic transition temperature. Phonon frequencies
calculated using the ab-initio and empirical potential model are in excellent
agreement with the reported experimental data. Further, volume dependence of
phonon dispersion relation has been calculated, which indicates softening of
zone boundary transverse acoustic phonon mode along [110] at volume
corresponding to the superionic transition in Li2O. The instability of phonon
mode could be a precursor leading to the dynamical disorder of the lithium sub
lattice. Empirical potential model calculations have been carried out to deduce
the probable direction of lithium diffusion by constructing a super cell
consisting of 12000 atoms. The barrier energy for lithium ion diffusion from
one lattice site to another at ambient and elevated temperature has been
computed. Barrier energy considerations along various symmetry directions
indicate that [001] is the most favourable direction for lithium diffusion in
the fast ion phase. This result corroborates our observation of dynamical
instability in the transverse mode along (110) wave vector. Using molecular
dynamics simulations we have studied the temperature variation of elastic
constants, which are important to the high-temperature stability of lithium
oxide.
