Li+ ion conductivity and diffusion mechanism in alpha-Li3N and beta-Li3N

beta-Li3N of hexagonal D-6h(4) (P6(3)/mmc) structure was synthesized by high-energy ball milling commercial Li3N (composed of both alpha and beta phases). Ionic conductivities of alpha-Li3N and beta-Li3N were tested by direct current (D. C.) and alternating current (A. C.) impedance methods. beta-Li3N exhibited the same order of magnitude of Li+ ion conductivity (2.085 x 10(-4) S cm(-1)) as that of alpha-Li3N (5.767 x 10(-4) S cm(-1)) at room temperature. First-principles calculations were employed to simulate the diffusion mechanism of Li+ ion in alpha-Li3N and beta-Li3N. Our results indicate that the diffusion of Li+ ion in beta-Li3N likely occurs between pure Li-beta(1) planes, which is different from that in alpha-Li3N, where the diffusion of Li+ ion occurs within Li2N plane. The Li+ ion migration energy barriers (E-m) for alpha-Li3N and beta-Li3N are 0.007 eV and 0.038 eV, respectively.