Pressure-induced metallization and amorphization in $\mathrm{V}{\mathrm{O}}_2\left(\mathrm{A}\right)$ nanorods

A metallic state enabled by the metal-insulator transition (MIT) in single crystal $\mathrm{V}{\mathrm{O}}_2\left(\mathrm{A}\right)$ nanorods is demonstrated, which provides important physical foundation in experimental understanding of MIT in $\mathrm{V}{\mathrm{O}}_2$. The observed tetragonal metallic state at ∼28 GPa should be interpreted as a distinct metastable state, while increasing pressure to ∼32 GPa, it transforms into a metallic amorphous state completely. The metallization is due to V $3d$ orbital electrons delocalization, and the amorphization is attributed to the unique variation of V-O-V bond angle. A metallic amorphous $\mathrm{V}{\mathrm{O}}_2$ state is found under pressure, which is beneficial to explore the phase diagram of $\mathrm{V}{\mathrm{O}}_2$. Furthermore, this work proves the occurrence of both the metallization and amorphization in octahedrally coordinated materials.

Figure 1

(a) XRD patterns of $\mathrm{V}{\mathrm{O}}_2\left(\mathrm{A}\right)$ at various pressure. The peaks of Fe and Ar are marked by asterisk and triangle, respectively. (b) HRTEM and (c) SAED images are corresponding to the sample released from 45.8 GPa.

Figure 2

(a) Raman spectra of $\mathrm{V}{\mathrm{O}}_2\left(\mathrm{A}\right)$ upon compression and decompression. (b) Pressure dependence of three modes above $800\mathrm{c}{\mathrm{m}}^{-1}$ upon compression.

Figure 3

(a) IR transmittance spectra of $\mathrm{V}{\mathrm{O}}_2\left(\mathrm{A}\right)$ upon compression. (b) Pressure dependence of the band gap upon compression. (c) IR reflectivity spectra of $\mathrm{V}{\mathrm{O}}_2\left(\mathrm{A}\right)$ upon compression. Insets: Drude fits in the metallic phase. The black solid lines represent the experimental data, the red dashed lines represent model fits to the data. (d) Reflectivity change at selected photon energies upon compression.

Figure 4

(a) Variation of relative lattice parameters $a/a_0$ and $c/c_0$ for $\mathrm{V}{\mathrm{O}}_2\left(\mathrm{A}\right)$ nanorods. (b) Pressure dependence of the bond angle of V-O-V in tetragonal phase upon compression.