Abstract
Materials that undergo reversible metal-insulator transitions are obvious candidates for new generations of devices. For such potential to be realised, the underlying microscopic mechanisms of such transitions must be fully determined. In this work we probe the correlation between the energy landscape and electronic structure of the metal-insulator transition of vanadium dioxide and the atomic motions occurring using first principles calculations and high resolution X-ray diffraction. Calculations find an energy barrier between the high and low temperature phases corresponding to contraction followed by expansion of the distances between vanadium atoms on neighbouring sub-lattices. X-ray diffraction reveals anisotropic strain broadening in the low temperature structure’s crystal planes, however only for those with spacings affected by this compression/expansion. GW calculations reveal that traversing this barrier destabilises the bonding/anti-bonding splitting of the low temperature phase. This precise atomic description of the origin of the energy barrier separating the two structures will facilitate more precise control over the transition characteristics for new applications and devices.
Highlights
The reversible phase transition of VO2 at ~340 K occurs between a low temperature, insulating monoclinic structure, and a high temperature, metallic tetragonal form[1,2,3]
The comparison illustrates that the structural rearrangements occurring in the transition from the tetragonal to the monoclinic structure orthogonal to the monoclinic a-axis can be summarized as an alternating off-set of the vanadium atoms from the centers of the oxygen octahedra
The (110)T and (011)M planes of the tetragonal and monoclinic structure are indicated with black lines, which reveals that they correspond to equivalent atomic spacings in each structure
Summary
The reversible phase transition of VO2 at ~340 K occurs between a low temperature, insulating monoclinic structure, and a high temperature, metallic tetragonal form[1,2,3]. The transition between between the insulating and metallic forms results in a switch from transparent to absorbing in the near infra-red[2,3,4], which can occur on time-scales as low as femtoseconds when triggered by laser pumping[5] While this transition was first identified by Morin in 19591, and explored more thoroughly in the 1970s by authors such as Goodenough[6], Pouget[7] and Mott[2], the last decade has seen an explosion of research into devices based upon this transition[8,9,10,11,12]. Chen et al.[31] explored the properties of the parameter space spanned by the β angle and the tetragonal c-axis using the DFT+U approach[32], and suggested that changing orbital occupancy is initially responsible for opening the band gap as a result of dimerisation, which is widened by a subsequent increase in the antiferroelectric distortion
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