Since OsB₂ shows a very large bulk modulus about 350 GPa, the related compound OsO₂ might be a potential candidate as a hard material.^[1] So, the phase transition of OsO₂ was studied via in situ synchrotron XRD under Mbar pressure range to search hard materials in this work.   In the compression process, OsO₂ transforms from the original rutile-type structure to a pyrite-type structure at about 24 GPa, and then to a fluorite-type structure at about 50 GPa. The estimated bulk modulus of 332 GPa for quenchable phase III suggests that fluorite-type OsO₂ is stiffer than some well-known hard materials such as B₆O and SiC. 

[1]Cumberland,R. et al. Osmium diboride, an ultra-incompressible, hard material. Journal of the American Chemical Society 127(20), 7264-7265 (2005).