Li3−xTi2(PO4)3 (0 ≤ x ≤ 1): A new mixed valent titanium(III/IV) phosphate with a NASICON-type structure

A new NASICON-related structure of lithium titanium phosphate Li_2.72Ti₂(PO₄)₃ has been determined. This compound crystallizes in an orthorhombic system, Pbcn, with a = 12.064 (3) Å, b = 8.663 (3) Å, c = 8.711 (4) Å, V = 910.4 (8) ų, and Z = 4. The single crystal structure of this novel mixed valent titanium(III/IV) phosphate reveals one titanium atom per asymmetric unit. Two lithium sites are characterized by a pair of distorted polyhedra, Li(1)O₄ and Li(2)O₅, which share a common edge resulting in a short Li(1) … Li(2) distance, i.e., 2.29 (5) Å. Magnetic susceptibility and microprobe analysis confirmed the structural composition. The room temperature ionic conductivity is comparable with that of the known Li_1+xTi^IV_2−xIn^III_x(PO₄)₃, which suggests possible fast ionic conductivity.