Elastic properties of VO2 from first-principles calculation

• The R, M1 and M2 phases are mechanically unstable with increasing pressure.
• The R and M2 phases of VO2 are predicted to be harder than the M1 phase.
• The anisotropy of the M2 phase is found to be larger than the M1 and R phases.

We used first-principles methods to calculate the elastic properties of rutile (R) structure and monoclinic (M1: space group P21/cP21/c, M2: space group C2/m) structure VO2, including single-crystal elastic constants cij's, polycrystalline bulk modulus, shear modulus, Young's modulus and elastic anisotropy ratio. We found that the energy difference among the R, M1 and M2 phases is small, indicating that it is easy to transit among them under a perturbation. Furthermore, from the pressure dependence of cij's, we also found that the structural instability (or phase transition) will occur when the volumes of the three phases are slightly smaller than their equilibrium volumes. Additionally, the R and M2 phases are predicted to be harder than the M1 phase, indicated by their larger bulk moduli and shear moduli. The elastic anisotropy of the M2 phase is larger than the M1 and R phases. The presently predicted elastic properties of VO2 provide helpful guidance for the strain energy estimation and stress analysis in nano-electronic devices.