Theoretical confirmation of a high-pressure rhombohedral phase in vanadium metal

Recent diamond-anvil-cell (DAC) experiments revealed a new phase in vanadium metal at high pressure. Here we present results from first-principles electronic-structure calculations confirming the existence of this phase. The structure corresponds to a rhombohedral distortion of the bcc ambient-pressure phase. The calculated transition pressure $\left(0.84\mathrm{Mbar}\right)$ and density compare reasonably with the measured data. Interestingly, a reentrant bcc phase is discovered at ultrahigh pressures above $2.8\mathrm{Mbar}$, close to the limit of DAC experimental capabilities. We show, extending prior work, that the phase transitions in vanadium are driven by subtle electronic-structure effects.

Figure 1

Enthalpy as a function of the rhombohedral deformation parameter $\delta$. The different curves correspond to the pressures indicated in the legend.

Figure 2

The order parameter for mechanically stable structures as a function of pressure at zero temperature. The order parameter is defined as $Q=\alpha ∕{\alpha }_0-1$, where ${\alpha }_0=109.47°$ is the axis angle of the bcc structure.

Figure 3

Experimental data from Ding et al. (Ref. 3) together with the present calculations.

Figure 4

Calculations showing the effect on the energy of including Cr within the virtual crystal approximation at $V=9.86{\mathrm{\AA }}^3$.