Potential superhard cubic spinel CSi2N4: First-principles investigations

Abstract

The structural and mechanical properties of the cubic spinel CSi2N4 (c-CSi2N4) are studied by first-principles total energy calculations based on the density-functional theory. It is found that the calculated lattice constants and bulk modulus are in good agreement with previous calculations. The elastic constants show that c-CSi2N4 is mechanically stable. Based on the microscopic hardness model, c-CSi2N4 is predicted to be a superhard material with the calculated Vickers hardness of 52.07GPa, which is 57.79% higher than that of the cubic spinel Si3N4. The origin of the hardness enhancement is discussed in terms of the density of states and the chemical bonding analysis. It is also found that the elastic anisotropy and the ductility are improved in comparison with those of the cubic spinel Si3N4.