What does it look like?
In 2006 a senior scientist remarked in the journal Nature ‘If that superconductors is made by doping concrete, I’ll know it’s time for me to retire’. We wonder if, the very next year, he was clearing his desk and getting his gold watch with the discovery of what happen when you dope today’s crystal structure.
Dodecacalcium hepta-aluminate (12CaO.7Al2O3) – often just known as C12A7, is another of those useful crystal phases that crop up in cement, along with tricalcium aluminate. It even occurs in nature, as the mineral Mayenite. In the structure the calcium and aliuminium oxides form cages, which hold small amounts of oxygen ions. A group in Japan, discovered that if you can replace the oxygen ions with electrons you can make the material behave like a metal, which is rather odd for concrete.
Then in 2007, the cooled the doped to 0.4 K and found that C12A7 becomes a superconductor! The key to this was how the electrons can move between the cages in the structure.
Where did the structure come from?