First-principles investigation of pressure-induced phase transition in LiNbO3

We explore the possible high-pressure phase transition of LiNbO3 using an evolutionary algorithm combined with first-principles calculations. A NaIO3-type structure with Pnma symmetry was predicted as the room temperature phase, and an apatite-like structure with P63/m symmetry was predicted as the high temperature, high-pressure phase. These predictions are consistent with the experimental findings of Mukaide et al. [J. Appl. Phys. 93, 3852 (2003)]. Interestingly, however, the thermodynamic stability of the Cmcm phase was found to be greater than that of the Pnma phase below 50 GPa. In order to explain this, we investigated the possible deformation paths between R3c and high-pressure phases and found that a high energy barrier hinders Cmcm formation, despite its greater thermodynamic stability. In sum, our results indicate that an understanding of the atomistic mechanisms behind phase transition is essential in order to correctly predict phase transition behavior.