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

摘要

The hardness, elastic moduli, and fracture toughness of the spinel phases, γ-Ge_3N_4 and γ-Sn_3N_4, 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-Ge_3N_4 and γ-Sn_3N_4 were found to be 295 and 167 GPa, respectively. The nanohardnesses of γ-Ge_3N_4 and γ-Sn_3N_4 were found to be 31 and 13 GPa, respectively. The shear moduli G_0 and Poisson's ratios v_0 were derived using theoretical bulk moduli B_0 obtained from density-functional theory calculations. The calculated values were B_0 = 260 GPa, G_0 = 146 GPa, v_0 = 0.26 for γ-Ge_3N_4, and B_0 = 186 GPa, G_0 = 64 GPa, v_0 = 0.34 for γ-Sn_3N_4. Fracture toughness was estimated by direct measurement of radial cracks emanating from Vickers microindents. It was determined that for γ-Ge_3N_4, K_(IC) = 2.3 MPa(m)~(1/2), while for γ-Sn_3N_4, K_(IC) = 1.4 MPa(m)~(1/2).