NaSnSbGeO, an Air-Stable Solid-State Na-Ion Conductor.

The structure of a NaSnGeO phase was established via single-crystal X-ray diffraction. Unusually large displacement parameters of Na atoms suggested the possibility of Na ionic conductivity. To create Na deficiencies and thus increase the Na mobility in NaSnGeO, Sn cations were partially substituted with Sb. A series of NaSnSbGeO samples ( = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, or 0.35) were prepared by solid-state reactions and characterized with electrical impedance spectroscopy in the range of 25-200 °C. The highest ionic conductivity value was achieved in the NaSnSbGeO sample (1.6 mS cm at 200 °C). Na migration pathways were calculated using the bond-valence energy landscape approach, and two-dimensional conductivity channels with low energy barriers (≈0.4 eV) were found in the structure. Three-dimensional conductivity can also be achieved in the structure; however, it has a much higher energy barrier. The pristine phase and NaSnSbGeO sample were studied via Na and Sn solid-state nuclear magnetic resonance. A faster exchange between the Na sites was observed in the doped sample.