SYNTHESIS, CRYSTAL-STRUCTURE, AND IONIC-CONDUCTIVITY OF A POLYCRYSTALLINE LITHIUM PHOSPHORUS OXYNITRIDE WITH THE GAMMA-LI3PO4 STRUCTURE

A crystalline form of lithium phosphorus oxynitride, Li-2.88 PO3.73N0.14, has been prepared by solid state reaction between Li3N and LiPO3 under a flowing N-2 atmosphere. The structure of the oxynitride was refined by Rietveld analysis of neutron powder diffraction data using the orthorhombic unit cell of gamma-Li3PO4 with space group Pmnb. High-performance liquid chromatography measurement indicates that most nitrogen substitutes for oxygen to form PO3N structural units with small concentrations of P-N=P due to some Li <----> P disorder in the structure. The ionic conductivity of Li2.88PO3.73N0.14 (sigma(25 degrees C) similar to 10-13 S . cm(-1)) is several orders of magnitude higher than that of gamma-Li3PO4 (sigma(25 degrees C) similar to 10(-18) S . cm(-1)). (C) 1995 Academic Press, Inc.