Geometric considerations of the monoclinic-rutile structural transition in VO

• Published in: Dalton transactions : an international journal of inorganic chemistry 2019-06, Vol.48 (25), p.926-9265
• Main Authors: Guan, Shian, Rougier, Aline, Suchomel, Matthew R, Penin, Nicolas, Bodiang, Kadiali, Gaudon, Manuel
• Format: Article
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt01241a

The mechanism of the displacive phase transition in VO 2 near the transition temperature is discussed in terms of a geometrical approach, combining simple calculations based on the Brown's band valence model and in situ X-ray diffraction experimental results. Considering that the structural origin is well linked to the electrostatic potential optimization as in a Peierls model, our geometrical calculations and experimental studies are in agreement and suggest that VO 2 phase transition is the consequence of very short atomic shifts mainly associated to a decrease of the 2 nd sphere coulombic interactions. Hence, at a given temperature, the allotropic form (monoclinic versus rutile form) offering the largest unit-cell volume is stabilized over the lower unit-cell volume allotropic, while the transition occurs at the intercept of the unit cell variation versus temperature of the two forms, which exhibit significantly different thermal expansion coefficients. Geometrical and experimental examinations of VO 2 show how hysteretic phase transition phenomena across the MIT can be driven by positive crystal energy effects of increasing unit cell volume.