STRUCTURAL-CHANGE BETWEEN NH4VO3 AND V2O5 STUDIED BY USING SINGLE-CRYSTALS

The structural changes between NH4VO3 and V2O5 are discussed from the results of decomposition and subsequent curing experiments starting wi th single crystals of NH4VO3 with well developed bc and ac planes. The structural change from NH4VO3 to V2O5 was divided into five steps, in cluding the first step up to 150 degrees C to keep the original NH4VO3 structure and the final 5th step to be V2O5. The preferred orientatio n of V2O5 crystallites in particles was found to be strongly influence d by the heating rate. The crystal heated up to the 2nd step (150-180 degrees C) could recover exactly the same single crystal by curing in saturated vapour of NH3-H2O at 25 degrees C. The curing of crystals he ated above the 4th step (above 210 degrees C) resulted in a polycrysta lline powder of NH4VO3. Structural changes during decomposition and cu ring between NH4VO3 and V2O5 are discussed.