Beta carbon nitride is a material predicted to be harder than diamond.

The material was first proposed in 1985 by Marvin Cohen

Marvin L. Cohen

Marvin L. Cohen is a Canadian-born American physicist. He is a professor of condensed matter physics and materials science at the University of California, Berkeley. Nobel laureate Robert B. Laughlin studied under John D. Joannopoulos, a student of Cohen's.Cohen received his PhD from the...

 and Amy Liu. Examining the nature of crystalline bonds

Covalent bond

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

 they theorised that carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 and nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 atoms could form a particularly short and strong bond in a stable crystal lattice in a ratio of 1:1.3. That this material would be harder than diamond

Diamond

In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...

 on the Mohs scale

Mohs scale of mineral hardness

The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...

was first proposed in 1989.

The material has been considered difficult to produce and could not be synthesized for many years. Recently, the production of beta carbon nitride was achieved. For example, nanosized beta carbon nitride crystals and nanorods of this material were prepared by means of an approach involving mechanochemical processing.