Electron Localization Induced by Uniaxial Stress in Pure VO2

NMR and EPR measurements in V${\mathrm{O}}_2$ under uniaxial stress in the ${\mathrm{}\left[110\right]\mathrm{}}_R$ direction lead to a phase diagram entirely similar to that obtained in ${\mathrm{V}}_{1-x}{\mathrm{Cr}}_x{\mathrm{O}}_2$ alloys. Two intermediate phases $M_2$ and $T$ are observed, and, as established for ${\mathrm{V}}_{1-x}{\mathrm{Cr}}_x{\mathrm{O}}_2$, correspond to linear Heisenberg chains of spin ½ ($M_2$ phase) on one V sublattice. These chains undergo a progressive dimerization in the $T$ phase as the temperature is lowered.