Fracture Strength of AlLiB14

TL;DR

This study uses first-principles calculations to determine the fracture strength and elastic properties of AlLiB$_{14}$, revealing its intrinsic strength is limited by B--B bonds, aligning with experimental hardness data.

Contribution

It provides the first comprehensive theoretical analysis of the fracture strength and elastic properties of AlLiB$_{14}$ using ab initio methods.

Findings

Lower bound fracture strength between 29 and 31 GPa

Intrinsic strength limited by B--B interatomic bonds

Predicted strength aligns with experimental hardness

Abstract

The orthorhombic boride crystal family XYB$_{14}$, where X and Y are metal atoms, plays a critical role in a unique class of superhard compounds, yet there have been no studies aimed at understanding the origin of the mechanical strength of this compound. We present here the results from a comprehensive investigation into the fracture strength of the archetypal AlLiB$_{14}$ crystal. First-principles, \textit{ab initio}, methods are used to determine the ideal brittle cleavage strength for several high-symmetry orientations. The elastic tensor and the orientation-dependent Young's modulus are calculated. From these results the lower bound fracture strength of AlLiB$_{14}$ is predicted to be between 29 and 31 GPa, which is near the measured hardness reported in the literature. These results indicate that the intrinsic strength of AlLiB$_{14}$ is limited by the interatomic B--B bonds that span between the B layers.