While "strength" can encompass various mechanical properties, such as tensile strength or toughness, research indicates that a specific high-pressure phase of C60 fullerite exhibits greater hardness than diamond.
Understanding Hardness vs. Strength
It's important to differentiate between material properties often colloquially grouped under "strength":
- Hardness refers to a material's resistance to localized plastic deformation, such as indentation or scratching. It measures how well a material resists permanent surface penetration.
- Strength (e.g., tensile, compressive, yield) describes a material's ability to withstand stress without fracturing or permanently deforming. For instance, tensile strength is the maximum stress a material can withstand before breaking under stretching.
When comparing C60 to diamond, the relevant property where C60 has shown superior performance under specific conditions is its hardness.
The Superhard C60 Fullerite Phase
Under extreme conditions, C60 (buckminsterfullerene) can transform into a material phase that surpasses the renowned hardness of diamond. This phenomenon is observed in a specific form of fullerite, which is a crystalline solid made of C60 molecules.
Key Characteristics of the Superhard Phase:
- Formation Conditions: This exceptionally hard state is achieved when fullerite is subjected to extremely high pressures, specifically pressures higher than 18 GPa (gigapascals).
- State of Matter: The superhard material is a transparent state of fullerite.
- Molecular Integrity: Even at these high pressures, it is believed that the C60 molecules themselves persist within the structure of the transparent fullerite.
- Hardness: This transparent, high-pressure state of fullerite exhibits a hardness that is unequivocally higher than that of diamond, which is widely recognized as the hardest known natural material.
This breakthrough demonstrates that specific structural arrangements of carbon, beyond the well-known diamond lattice, can lead to materials with extraordinary mechanical properties, even exceeding diamond's legendary hardness under certain conditions.
