Studies on Vanadium Oxides. I. Phase Analysis.

Abstract

The phase relations in the composition range VO-VO(2.50) of the vanadium-oxygen system have been investigated. Phases of the following (approximate) compositions were found to exist at temperatures between 650-1000ºC: VO (homogeneous within the range VO0.75-VO1.20), VO1.50, *VO1.67, *VO1.75, *VO1.80, *VO1.84, *VO1.86, *VO1.87, *VO2.00, *VO2.17 (at 650ºC), and VO2.50; the formula marked with an asterisk represent previously unknown oxides. The VO1.67 phase is monoclinic with the C centered unit cell dimensions: a=9.983A; b=5.031A; c=9.835A; beta=138.80º. The formula of this phase is probably V3O5 and the unit cell thus contains 4 V3O5. Powder photographs of the phases VO1.75-VO2.00 suggest pronounced structural relationships to exist between these oxides. They may represent oxides belonging to a series with the general formula VnO2n-1. The VO2 phase is monoclinic with the unit cell dimensions: a=5.743A; b=4.517A; c=5.375A; beta=122.61º and the observed reflections are in accordance to the space-group P21/c. The unit cell contains 4 VO2. The V6O13 phase has been found to decompose into VO2 and V2O5 at 700ºC and higher temperatures.