Li 3 N is a structurally and compositionally-simple longstudied superionic conductor . It has three phases: the αand the β-phase (Figure ), which we consider here, and the γ-phase, which is only stable under high pressure at about 35 GPa , and which we therefore will not discuss further. The α-phase consists of alternating Li 2 N layers and pure Li layers. The α-phase conducts ions in its Li 2 N plane at a rate of 1.2 × 10 -3 S cm -1 at 300 K . For several decades, it remained the highest Li ionic conductivity measured in a crystal around room temperature. Commercial applications, however, have been hindered by a low electrochemical stability, 0.45 V versus Li + /Li . The β-phase has a similar structure but exhibits another pure Li layer in between each Li 2 N plane. It conducts ions in its pure Li layer at a rate of 2.085 × 10 -4 S cm -1 . It is clear from the structures of the two phases that they are related by a first order structural phase transition.