High Pressure Structure of Half-Metallic CrO2

Evidence for a structural phase transition from rutile {alpha}-CrO{sub 2} phase I (P4{sub 2}/mnm) to orthorhombic {beta}-CrO{sub 2} phase II (CaCl{sub 2}-like, Pnnm) is presented using angle-resolved synchrotron x-ray diffraction and high sensitivity confocal Raman spectroscopy. The transition to the CaCl{sub 2} structure, which appears to be second-order, occurs at 12 {+-} 3 GPa without any measurable discontinuity in volume, but is accompanied by an apparent increase in compressibility. Raman data are also presented to show further evidence for a second-order structural phase transition as well to demonstrate soft-mode behavior of the B{sub 1g} phonon mode