In this paper, olivine-type LiInSiO4 and LiInGeO4 as fast ionic conductors are predicted by ab initio density functional studies. The nudged elastic band approach showed extremely small energy barrier for lithium ion hopping to neighboring sites with 0.23 eV for LiInGeO4 and 0.36 eV for LiInSiO4. However, formation energy for the intrinsic defects including lithium ion vacancy sites is expected to be large (more than similar to 1.5 eV), which suppresses ionic conductivity severely. Therefore it is expected that doping these olivine-type materials with higher valent cations may be a better option to create lithium ion vacancies.
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