TRANSITION-METAL DIOXIDES WITH A BULK MODULUS COMPARABLE TO DIAMOND

Recently it has been reported that a high-pressure cubic phase of ruth enium dioxide has an unusually large bulk modulus, and consequently is a most interesting candidate as a very hard material. Based on ab ini tio calculations it is shown that the high bulk modulus is a result of a strong covalent bonding between ruthenium d states and oxygen p sta tes in combination with the favorable geometry of the orbitals in the fluorite structure. In addition an even higher bulk modulus is predict ed for the isoelectronic and isostructural compound OsO2.