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The pressure dependencies at room temperature of Raman and infrared (IR) data on VO 2 are presented up to 19 and 15 GPa, respectively, together with preliminary X-ray diffraction (XRD) data collected up to 42 GPa. Both Raman and XRD indicate the persistence of a monoclinic lattice up the highest pressures. Observed modifications in the pressure dependence of Raman phonon frequencies, IR spectral weight, and unit cell volume at ∼10 GPa allow us to identify two regimes at low and high pressure and to conjecture a transition to a new unknown monoclinic phase where applying pressure activates a metallization mechanism.

Transition metal oxides often display insulator to metal transitions (MIT) with conductivity jumps up to several orders of magnitude, which makes them very attractive both for technological applications and for the several fundamental issues they raise. Information about the mechanism inducing the MIT may be gained by means of infrared (IR) spectroscopy. We present here the capabilities of the IR synchrotron source SISSI (Synchrotron Infrared Source for Spectroscopy and Imaging), at the Italian storage ring ELETTRA. We demonstrate SISSI to be a powerful source for optical studies of pressure-induced insulator-to-metal transitions, reporting on V3O5 and (V0.989Cr0.011)2O3 as examples.

The pressure-induced changes in the optical response of magnetite were studied by infrared reflectivity measurements at room temperature. The pressure-induced redshift of the pronounced midinfrared absorption band confirms the polaronic transport mechanism. The low-frequency conductivity increases and the phonon modes harden with increasing pressure. We discuss our results in terms of the proposed pressure-induced charge transfer among the different Fe sites.