The effect of the structure upon ionic conduction in crystalline γ-Li3PO4 and Li2.88PO3.73N0.14 was analyzed by using approximate molecular orbital calculations. A model was constructed, starting from γ-Li3PO4, for the new non-stoichiometric oxynitride, Li11P4O14N, in which an O in a bridging position (O11) in the parent γ-Li3PO4 structure was replaced by a N atom. In addition, O and Li defects were introduced in a systematic manner. The distortion of the lattice, in response to substitution and defect formation, was examined. In order to study the P-N-P units which were detected in chromatographic studies of the oxynitride, density functional calculations were also carried out on small-cluster models: [(HO)3PNP(HO)3)]+, [(HO)3POP(HO)3)]2+, [OP3(OH)3)]4+ and [NP3(OH)3)]3+. The calculations suggested that a high concentration of defects was required in order to produce a high mobility of Li species across tetrahedral faces, rather than edges.

Electronic and Structural Effects of Nitrogen Doping on the Ionic Conductivity of γ-Li3PO4. H.Rabaâ, R.Hoffmann: Journal of Solid State Chemistry, 1999, 145[2], 619-28