Lithium-Ion Conduction Pathways in Complex Lithium Spinels Li2MGe3O8 (M = Ni or Zn)

Crystal structures of Li2MGe3O8 (M = Ni or Zn), in space group P4332, have been refined by application of the Rietveld method to variable-temperature time-of-flight neutron powder diffraction data. Difference Fourier maps, calculated using data collected at high temperatures, showed significant negative density centered at positions vacant at ambient temperatures. In Li2NiGe3O8, conduction involves three-dimensional 8c–12d–8c site hopping, facilitated by harmonic oscillations of oxygen atoms away from their ideal positions. For Li2ZnGe3O8, the pathway involves a more complex 4b–24e–4a–24e–4b mechanism.