*

VO₂ is well known for its reversible first order metal to insulator transition (MIT) along with a structural phase transition (SPT) between low-temperature monoclinic, M1 to high-temperature rutile tetragonal, R phase at 340K. Besides M1, another two low temperature phases of monoclinic M2 and triclinic T also evolve during the phase transition. It is argued that MIT is driven by strong electronic correlation compatible with Mott mechanism, resolving a long-standing “chicken-and-egg” debate in VO₂. Insulating phase of VO₂ can be considered as a collection of 1-D half-filled band, which undergoes first order Mott transition to 1-D infinitely long Heisenberg spin ½ chains leading to structural distortion due to spin-phonon coupling.

We report here that even though the MIT is first order Mott type phase transition, the structural transition is of second order, as confirmed from a continuous change in the volume and a discontinuity in the bulk modulus around structural transition with hydrostatic pressure. The transition pressure for the structural change from M2 to M1 is found out at ~2.8 GPa. A first order MIT prompts a second order SPT leading to SPT and MIT observed at the same time in VO₂.