Hardness, elasticity, and fracture toughness of polycrystalline spinel germanium nitride and tin nitride

Abstract

The hardness, elastic moduli, and fracture toughness of the spinel phases, γ–Ge3N4 and γ–Sn3N4, were determined using indentation data and theoretical calculations. Measurements were performed on polycrystalline specimens using the technique of nanoindentation to determine the reduced moduli and hardnesses from the unloading portion of the indent curves. Reduced moduli of γ–Ge3N4 and γ–Sn3N4 were found to be 295 and 167 GPa, respectively. The nanohardnesses of γ–Ge3N4 and γ–Sn3N4 were found to be 31 and 13 GPa, respectively. The shear moduli G0 and Poisson’s ratios ν0 were derived using theoretical bulk moduli B0 obtained from density-functional theory calculations. The calculated values were B0 = 260 GPa, G0 = 146 GPa, ν0 = 0.26 for γ–Ge3N4, and B0 = 186 GPa, G0 = 64 GPa, ν0 = 0.34 for γ–Sn3N4. Fracture toughness was estimated by direct measurement of radial cracks emanating from Vickers microindents. It was determined that for γ–Ge3N4, KIC = 2.3 MPa(m)1/2, while for γ–Sn3N4, KIC = 1.4 MPa(m).1/2