Ultralow compressibility silicate without highly coordinated silicon

The bulk modulus of scheelite-structured ZrSiO4 is 301.4 +/- 12.5 GPa, as derived from static compression experiments to 52.5 GPa. It is as stiff as the most incompressible known silicate, SiO2 stishovite. This high incompressibility indicates that octahedrally coordinated silicon is not required to generate ultrastiff silicates: ZrSiO4 scheelite is the most incompressible material containing SiO4 tetrahedra. Its incompressibility is in accord with a semitheoretical relation we derive for the bulk modulus of scheelite-structured materials. Based upon correlations between incompressibility and hardness, scheelite-structured oxides may thus represent a new family of ultrahard materials.