Selective formation of VO{sub 2}(A) or VO{sub 2}(R) polymorph by controlling the hydrothermal pressure

Journal Article · Mon Aug 15 00:00:00 EDT 2011 · Journal of Solid State Chemistry

OSTI ID:21580192

Shidong, Ji ^[1]; Feng, Zhang ^[2]

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1. College of Materials Science and Technology, Nanjing University of Technology, No. 5, New Mofan Road, 210009 Nanjing (China)
2. Department of Scientific and Engineering Simulation, Nagoya Institute of Technology, Gokiso-Cho, Showa-ku, Nagoya 466-8555 (Japan)

Missing VO{sub 2}(A) usually occurs during the preparation of VO{sub 2} polymorphs. This leads to an ambiguous understanding of the transformation between VO{sub 2} polymorphs. The calculation of the ground state energies for different VO{sub 2} polymorphs indicated that there is only a small energy gap between VO{sub 2}(A) and VO{sub 2}(R), which destined that the transformation from VO{sub 2}(A) to VO{sub 2}(R) should be pressure sensitive. This hypothesis was verified during the synthesizing of VO{sub 2} polymorphs by reducing V{sub 2}O{sub 5} with oxalic acid through hydrothermal treatment process. Selective formation of pure phase VO{sub 2}(A) or VO{sub 2}(R) was achieved by controlling the hydrothermal pressure through varying the filling ratio at 270 deg. C. It was found that a filling ratio over 0.5 favors the formation of pure VO{sub 2}(R) while a reduced filling ratio to 0.4 or lower results in the formation of VO{sub 2}(A). Based on our experiments, VO{sub 2}(B) nanobelts were always first formed and then it transformed to VO{sub 2}(A) by assembling process at increased temperature or extended reaction time. Under further higher pressure, the VO{sub 2}(A) transformed spontaneously to VO{sub 2}(R) initialized from the volume shrinkage due to the formation of denser VO{sub 2}(R). - Graphical abstract: Selective formation of VO{sub 2}(A) or VO{sub 2}(R) could be achieved by controlling the system pressure through varying the filling ratio during hydrothermal treatment. Highlights: > Selective formation of VO{sub 2} polymorphs by controlling hydrothermal pressure. > Ground state energy characteristics were revealed for the first time. > Phase transformation mechanism was clearly elucidated.

• OSTI ID: 21580192
• Journal Information: Journal of Solid State Chemistry, Vol. 184, Issue 8; Other Information: DOI: 10.1016/j.jssc.2011.06.029; PII: S0022-4596(11)00357-4; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ENERGY GAP
HYPOTHESIS
NANOSTRUCTURES
OXALIC ACID
PHASE TRANSFORMATIONS
SHRINKAGE
VANADATES
VANADIUM OXIDES
CARBOXYLIC ACIDS
CHALCOGENIDES
DICARBOXYLIC ACIDS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS