Synthesis, structure, and ionic conductivity of Na5Li3Ti2S8

The compound Na5Li3Ti2S8 has been synthesized by the reaction of Ti with a Na/Li/S flux at 723 K. Na5Li3Ti2S8 crystallizes in a new structure type with four formula units in space group C2/c of the monoclinic system. The structure contains three crystallographically independent Na+ cations and two crystallographically independent Li+ cations. Na5Li3Ti2S8 possesses a channel structure that features two-dimensional image layers built from Li(1)S4 and TiS4 tetrahedra. The layers, which are stacked along c, comprise eight-membered rings and sixteen-membered rings. Na(3)+ cations are located between the eight-membered rings and Na(1)+, Na(2)+, and Li(2)+ cations are located between the sixteen-membered rings. These cations are each octahedrally coordinated by six S2− anions. The ionic conductivity σT of Na5Li3Ti2S8 ranges from 8.8×10−6 S/cm at 303 K to 3.8×10−4 S/cm at 483 K. The activation energy Ea is 0.40 eV.