Elastic Moduli and Hardness of Cubic Silicon Nitride

The bulk modulus B 0 = 290(5) GPa and its first pressure derivative B ′ 0 = 4.9(6) were obtained for c ‐Si 3 N 4 from volume versus pressure dependence. Measurements were performed under quasi‐hydrostatic conditions in a diamond anvil cell to 53 GPa using synchrotron radiation and energy dispersive X‐ray powder diffraction. This combined with nanoindentation measurements determined the shear modulus G 0 of c ‐Si 3 N 4 to be 148(16) GPa. The Vickers microhardness H V (0.5) for dense, oxygen‐free c ‐Si 3 N 4 was estimated to be between 30 and 43 GPa. Both the elastic moduli and microhardness of c ‐Si 3 N 4 exceed those of the hexagonal counterparts, α‐ and β‐phases.