Mechanical properties and atomistic deformation mechanism of γ-Y 2Si 2O 7 from first-principles investigations

Abstract

The theoretical mechanical properties and atomistic shear deformation mechanisms of γ-Y 2Si 2O 7, one of the most refractory silicates and potentially useful as a high-temperature structural ceramic, were investigated using first-principles calculations. The material shows low shear moduli to bulk modulus ratios, as well as a low ideal shear strength to tensile strength ratio. The unusual low shear deformation resistance of γ-Y 2Si 2O 7 originates from the inhomogeneous strength of its chemical bonds. The Y–O bond is weaker and readily stretches and shrinks; and Si–O bond is stronger and more rigid. The relative softer YO 6 octahedron positively accommodates shear deformation by structural distortion, while the Si 2O 7 pyrosilicate unit is more resistant to deformation. The reported shear-load-bearing mechanism is quite similar to those found in the “quasi-ductile” LaPO 4 monazite and ternary layered carbides (the so-called MAX phases), and can endow γ-Y 2Si 2O 7 with quasi-ductility and damage tolerance.