Phase transitions and Raman spectra of anatase and rutile at high pressures and room temperature

High-P phase transitions of anatase and rutile at room T under a hydrostatic environment to 115 kbar have been studied using Raman spectroscopy. Anatase transforms to a columbite-type TiO (sub 2) at 54 +- 2 kbar; the transition is virtually instantaneous but is reversible. Rutile also transforms to this phase but sluggishly and irreversibly, starting near 100 kbar. New data for the P dependences of the various Raman bands of columbite-type TiO (sub 2) are reported; each of these phases has one very weak Raman band and its wave number decreases linearly with increasing P. These weak bands appear to vanish at high P in anatase and the columbite- type TiO (sub 2) .