Electronic structures of superionic conductor Li$_3$N

Lithium nitride is a superionic conductor with high Li conductivity. The compound has been studied extensively because of its potential utility as electrolyte in solid-state batteries. Though the mobility of the cations within the crystalline solid is high comparable to that of molten salts, the mechanism of the high mobility of the cations remains unsolved. To clarify the origin of the mobility we investigate the electronic states of the Li cations in the Li$_3$N crystal with the first principles electronic structure analysis, focusing a correlation between the cations and the ionicities of the constituent atoms. We have found the existence of the covalent bonding between the Li atoms in the Li$_3$N crystal in spite of the ionized states of the constituent atoms.