Effects of size ratio on particle packing in binary glasses

Abstract

Mixtures of binary spheres represent prototypes of amorphous solids and can model metallic, granular, and colloidal glasses. However, the effects of the size ratio λ on amorphous structures are not well understood. Here, we revisit the controversial noncubic scaling law and the local sphere packing by systematically changing λ. Our simulations clarify the existence and mechanism of the noncubic scaling law for mean atomic volume, va∝q1−d, where q1 is the position of the first diffraction peak and d is a constant less than the space dimension D. We find that the scaling law holds at each λ in binary hard-sphere glasses and metallic glasses, but the exponent satisfies a universal power law, d∼(λ−λc)−γ, instead of being a constant. The decreasing trend of d(λ), the abnormal d>D and the divergence of d when λ approaches 1 are theoretically explained. Moreover, d begins to fluctuate at λ<1.2, indicating less stable glasses. Large and small spheres are better dispersed with more disordered structures at λ>1.2. At λ=1.2, various structural parameters change, and the number of icosahedral packing reaches the maximum. The results cast light and pose new challenges on amorphous structures of binary glasses.