Pressure-induced cation-cation bonding in ${\mathrm{V}}_2{\mathrm{O}}_3$

A pressure-induced phase transition, associated with the formation of cation-cation bonding, occurs in ${\mathrm{V}}_2{\mathrm{O}}_3$ by combining synchrotron x-ray diffraction in a diamond anvil cell and ab initio evolutionary calculations. The high-pressure phase has a monoclinic structure with a $C2/c$ space group, and it is both energetically and dynamically stable at pressures above 47 GPa to at least 105 GPa. This phase transition can be viewed as a two-dimensional Peierls-like distortion, where the cation-cation dimer chains are connected along the $c$ axis of the monoclinic cell. This finding provides insights into the interplay of electron correlation and lattice distortion in ${\mathrm{V}}_2{\mathrm{O}}_3$, and it may also help to understand novel properties of other early transition-metal oxides.

Figure 1

Pressure evolution of diffraction profile in a helium medium. Left inset: compression of the V-O bonds up to 13 GPa. The standard deviations of bond lengths and $c/a$ are less than the size of the symbols. Right inset: pressure evolution of the axial ratio.

Figure 2

X-ray diffraction patterns of ${\mathrm{V}}_2{\mathrm{O}}_3$ as a function of pressure at room temperature (left panel, compression; right panel, decompression).

Figure 3

(a) Comparison of theoretical and experimental x-ray powder diffraction patterns of the high-pressure phase ${\mathrm{V}}_2{\mathrm{O}}_3$. (b) The V-V bond structure in high-pressure monoclinic ${\mathrm{V}}_2{\mathrm{O}}_3$. The teal and red balls represent the vanadium and oxygen atoms, respectively. (c) The pressure evolution in the relative enthalpies of high-pressure and low-temperature monoclinic structures from static calculations. The dashed line indicates zero enthalpy difference. (d) Phonon-dispersion curves for the high-pressure monoclinic structure at 50 GPa.

Figure 4

(a) Each vanadium atom in ${\mathrm{V}}_2{\mathrm{O}}_3$ has three nearest neighbors with three bond lengths ($R1, R2$, and $R3$), with blue spheres representing the vanadium atom. The puckered honeycomb lattices in the basal plane for (b) the room-temperature phase with $R1=R2=R3$, (c) the low-temperature phase with $R2>R1\approx R3$ below 150 K, and (d) the high-pressure phase with $R3<R2<R1$ above 47 GPa. For simplicity, oxygen atoms are not shown.

Figure 5

The partial charge densities and density of states (DOS) of the high-pressure phase ${\mathrm{V}}_2{\mathrm{O}}_3$ at 50 GPa. The isosurfaces of the partial charge densities in the HP phase ${\mathrm{V}}_2{\mathrm{O}}_3$ are shown for (a) the energy range of $-2.8$ to $-0.7$ eV at the isosurface level of 0.03 $e/{\AA }^3$, and (b) the energy range of $-0.7$ to 0 eV at the isosurface level of 0.007 $e/{\AA }^3$. Only the V atom are shown (blue spheres). For simplicity, oxygen atoms are not shown. (c) The total DOS of the HP phase ${\mathrm{V}}_2{\mathrm{O}}_3$ at 50 GPa. $\alpha ,\beta$ and $\alpha$*,$\beta$* represent bonding and antibonding orbitals, respectively.