Diamonds may be forever, but that doesn’t mean they’re the only game in town. Researchers Yasumaru Fujii, Mina Maruyama, and colleagues at the University of Tsukuba have made computer models of a new 3-D carbon structure they call pentadiamond whose properties promise to outshine those of the original material (Phys. Rev. Lett. 2020, DOI: 10.1103/PhysRevLett.125.016001). Unlike a typical diamond, in which every carbon is bonded to four other carbons, a pentadiamond has a mix of carbons bound to three and four other carbons. These form a network of five-membered carbon rings—hence the name pentadiamond. Using density functional theory calculations, the scientists calculated that, if it can be made, a pentadiamond should be stiffer than a standard diamond. They also predict it has better semiconductor properties than diamonds, possibly making it useful in electronics, like displays. And because a pentadiamond’s crystal structure has larger cavities than a standard diamond's, the new material should be about one-third lighter. The researchers did not attempt to make a pentadiamond in the lab, but they suggest it could be done using nickel-catalyzed reactions between ring-bearing molecules.