The Phase Transitions between H0.13V0.13Mo0.87O3·0.26H2O and MoO3: An X-Ray, Thermal Analysis, and TEM Study

✍ Scribed by L. Dupont; D. Larcher; M. Touboul

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 939 KB
• Volume: 143
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.8067

✦ Synopsis

Mixed vanadium-molybdenum oxide hydrates (H x V x Mo 1؊x O 3 • 0.26H 2 O with 0.064 4x4 40.18) have been synthesized by a soft chemistry method. The phase transitions from one of these hydrates (x ‫؍‬ 0.13) to the final product MoO 3 have been studied by thermal analysis, X-ray powder diffraction, and transmission electron microscopy techniques. Both metastable and stable oxides have been observed. H 0.13 V 0.13 Mo 0.87 O 3 • 0.26H 2 O possesses a structure related to hexagonal MoO 3 . Dehydration of the precursor leads to a metastable phase H 0.13 V 0.13 Mo 0.87 O 3 , with a structure similar to that of the hydrate. At 500°C this phase transforms into the metastable V 0.13 Mo 0.87 O 2.935 , with a structure related to the orthorhombic MoO 3 structure. The heating of this last phase above 500°C induces a change from the metastable system to the stable binary (V 2 O 5 -MoO 3 ) one. In agreement with this binary, a liquid phase and a solid phase with a composition closest to MoO 3 , are formed during the phase segregation at 600°C. Models for explaining these phase transitions are proposed.