Electronic And Ionic Conductivity In Alkaline Earth Diazenides Maen2 (M-Ae = Ca, Sr, Ba) And In Li2n2

Electrical conductivity measurements of alkaline earth diazenides SrN2 and BaN2 revealed temperature-dependent metal-like behavior. As CaN2 is isotypic with SrN2 its electronic properties are supposed to show similar characteristics. For the alkali diazenide Li2N2, the corresponding measurement shows not only the typical characteristics of metallic materials but also an unexpected rise in electrical conductivity above 250 K, which is consistent with an ionic contribution. This interpretation is further corroborated by static Li-6 and Li-7 nuclear magnetic resonance measurements (NMR) of the spin-lattice relaxation time (T-1) over an extended temperature range from 50 to 425 K. We observe a constant Heitler-Teller product (T1T) as expected for metals at low temperatures and a maximum in the temperature-dependent relaxation rates, which reflects the suggested ionic conductivity. A topological structural analysis indicates possible 3D ion migration pathways between two of the three crystallographic independent Li positions. A crude estimate of temperature-dependent self-diffusion coefficients D(T) of the lithium motion classifies Li2N2 as a mixed electronic/ionic conductor.