New ternary nitride ceramics: CaSiN2

The synthesis of CaSiN2 powder, starting from metal nitrides, is described. Fully dense CaSiN2 ceramics can be sintered from the prepd. powder at 1700 DegC. The samples were sintered in a closed Mo vessel to prevent evapn. of calcium nitride. The phase compn., and the chem. and mech. properties of the as-prepd. ceramics are described. The thermal cond. at room temp. was evaluated as 2.4 W m-1 K-1. A reasonable strength of 179 MPa and a fairly good fracture toughness of about 2.1 MPam1/2 were found. A hardness of 9.6 GPa and a Young's modulus of 174 GPa were measured. The value of the relative dielec. const. was measured as 13.3. The bandgap for CaSiN2 at room temp. was estd. from diffuse reflectance spectra to be 4.5 eV. Considerable improvement in the properties are expected when the processing conditions which is well within reach are optimized. [on SciFinder (R)]