A NEW POLYMORPH OF VO2 PREPARED BY SOFT CHEMICAL METHODS

A novel polymorph of VO2, designated VO2(C), has been prepared by dehy dration of the new layered vanadium oxide hydrate, VO2 . 1/2 H2O. The hydrate is prepared in high yield as a single phase from the hydrother mal reaction of the hydrolyzate of VCl4 and NaOH in a molar ratio of 1 :4.5 for 96 hours at 200 degrees C. The hydrate crystallizes in the te tragonal space group I4/mmm, with a = 3.7211(6) Angstrom, 15.421(1) An gstrom, Z = 4, and R = 0.045 as determined by X-ray single crystal dif fraction. The structure consists of layers of VO5 square pyramids, eac h of which shares its four basal edges,vith four neighboring VO5 squar e pyramids. Water molecules that reside between the layers can be remo ved reversibly to give the new layered oxide VO2(C). (C) 1998 Academic Press.