Phase transitions in ruthenium dioxide up to 40 GPa: Mechanism for the rutile-to-fluorite phase transformation and a model for the high-pressure behavior of stishovite SiO2

${\mathrm{RuO}}_{2}$ was studied up to 40.2 GPa by angle-dispersive x-ray diffraction. Two phase transitions were observed, the first from the rutile-structured ambient phase to an orthorhombic phase below 8.0 GPa with cell parameters a=4.615(17), b=4.230(13), and c=3.112(4) \AA{}, Z=2 at 11.3 GPa. ... View More