Revealing the atomic-scale origin of simultaneously enhanced hardness and crack resistance in a single phase material

Overcoming the brittleness of glass materials has always been one of the most important scientific questions in the field of materials physics. Herein, we selected a silica (SiO2) crystal, a silica glass, a sapphire (Al2O3) crystal, an amorphous alumina film, and a CaO.Al2O3 (CA) glass as the research objects. Detailed characterization was performed on two kinds of macromechanical properties, i.e., hardness and crack resistance. Combined with their density, bond density, bond energy density, and other structural features, we systematically investigated the structural origin and physics mechanism of hardness and crack resistance in a single phase material. The structural origin of the inverse relationship between hardness and crack resistance is ascribed to the facts that the bond density in a single phase material is generally positively correlated with the hardness while usually negatively correlated with the crack resistance. The discovery of simultaneously high hardness and high crack resistance in a CA glass revealed the key way to break through the inverse relationship between hardness and crack resistance, i.e., to develop the materials with the capability of self-adaptive structural adjustment, thus dissipating as much energy as possible upon external impact. These findings pave the way to the development of "scratchproof" and "unbreakable" transparent window materials such as a mobile phone screen glass.