SYNTHESIS, CRYSTAL-STRUCTURE, ELECTRICAL, MAGNETIC, AND ELECTROCHEMICAL LITHIUM INTERCALATION PROPERTIES OF VANADIUM OXYNITRIDES

Polycrystalline vanadium oxynitrides have been prepared by heat-treati ng V2O5 at high temperature in a flowing ammonia atmosphere. Single-ph ase cubic samples, with the rock salt structure, were produced by nitr idation at 600-700 degrees C. Powder diffraction data from neutrons at two wavelengths and CuK alpha X-rays of these oxynitrides were analyz ed using the Rietveld method, but strong correlation among the atomic displacement parameters, site occupancies, and the N/O ratio did not a llow a refinement of unique compositions. Measured densities and cell volumes were used to limit the possible compositional space for each s ample, and these were further limited by the charge neutrality require ment. The electrical resistivity of the single-phase sample is about 2 x 10(-3) Ohm . cm and is weakly temperature dependent below room temp erature. Magnetic susceptibility measurements show no evidence of magn etic ordering and yield a magnetic moment of 0.25 mu(B) per V atom. El ectrochemical lithium intercalation measurements indicate that only a small concentration of lithium ions were inserted into the cathode due to the close-packed NaCl structure of cubic vanadium oxynitride. (C) 1996 Academic Press, Inc.