Experimental and theoretical investigation of the mechanical characteristics of sillenite compound: Bi12GeO20

Highlights: • Bi₁₂GeO₂₀ (BGO) compound was investigated by density functional theory calculations. • The mechanical and anisotropic elastic characteristics of BGO were reported. • DFT studies presented shear and Young's moduli, linear compressibility, hardness. • Hardness and Young's modulus were also obtained by performing nanoindentation experiments. -- Abstract: The present study reports the mechanical and elastic characteristics of Bi₁₂GeO₂₀ (BGO) compound by experimental nanoindentation measurements and density functional theory (DFT) calculations. X-ray diffraction pattern of BGO was plotted and revealed diffraction peaks were associated with Miller indices of cubic crystalline structure with lattice constant of a = 10.304 Å. Two- and three-dimensional representations of Young's modulus, linear compressibility, shear modulus and Poisson's ratio were presented according to DFT calculations. The calculated elastic constants pointed out the mechanically stable and anisotropic behavior of the BGO. The hardness and Young's modulus ranges of the BGO calculated from DFT studies were found as 3.7–6.3 GPa and 61.7–98.9 GPa, respectively. Hardness and Young's modulus of BGO single crystal were also obtained by analyzing force-dependent nanoindentation experimental data. It was observed that hardness and Young's modulus decrease with increase of load in the low applied loads and then reaches saturation in the high applied loads. This behavior is known as indentation size effect. True hardness value was determined from proportional specimen resistance model as 4.1 GPa. The force independent region presented the Young's modulus as 114 GPa.