Mo(V) Phosphates with an Opened Framework: Li4-xA+x(MoO)3(PO4)3P2O7(A=Na, Ag, Cs, K), Li4-xBa2+x/2(MoO) 3(PO4)3P2O7

The exploration of Li–A–Mo–P–O systems has allowed several Mo(V) phosphates, Li4-xAx(MoO)3(PO4)3P2O7(A= Na, Ag, Cs, K) and Li3Ba0.5(MoO)3(PO4)3P2O7, to be synthesized. Two types of closely related structures are evidenced depending on the nature and content of theAcation. The type I structure has been refined from single-crystal X-ray refinements for Li3Ba0.5(MoO)3(PO4)3P2O7. It exhibits a [Mo3P5O22]framework built up from [Mo2P2O15]slices interconnected through [Mo2P6O25]ribbons forming six-sided Z-shaped tunnels. This structure is also observed for other phosphates, Li4-xAx(MoO)3(PO4)3P2O7withA=Na, K, Cs, Ag, but it is associated with a certain order–disorder phenomena, evidenced by the existence of streaks in ED patterns. The type II structure, observed for Li2.5K1.5(MoO)3(PO4)3P2O7, exhibits the same [Mo2P2O15]slices as type I, and differs only from the latter by the positions of the [Mo2P6O25]ribbons which interconnect the [Mo2P2O15]slices. For this compound, streaks are also observed in ED patterns. Taking into consideration the close relationship between the two structures, a model based on the coexistence of the two structures in the same matrix ("intergrowth" defects) is proposed to explain the disorder phenomena. Magnetic measurements confirm the only presence of Mo(V). Ionic conductivity, due to lithium mobility, is evidenced for several phosphates withvalues ranging from 1.3×10-5to 4.1×10-5(/cm)-1at 300°C, andEaranging from 0.73 to 0.89 eV.