Barium titanate

Barium titanate is a white ceramic made of barium, titanium and oxygen, BaTiO₃. Its atoms form a cube-like arrangement called a perovskite, with a small titanium atom in the middle of a cage of oxygen atoms. That titanium can shift slightly off-center in an electric field, which lets the material store a lot of charge. Its dielectric constant can run into the thousands, compared with 1 for a vacuum.

It's made from two powders. Barium carbonate supplies barium, and titanium dioxide supplies titanium and oxygen. They are finely milled together and heated to around 1,000 to 1,200 °C. The atoms rearrange into barium titanate, and carbon dioxide gas escapes from the carbonate. For the thinnest capacitor layers, makers need grains of a few hundred nanometers or smaller, often made by wet chemical routes that give better control. Small amounts of other elements are added to tune how it behaves as temperature changes.

It's the insulating layer inside every ceramic capacitor in the TV. Discovered in the 1940s, it was one of the first ferroelectric materials found and is still the most widely used. It's also piezoelectric, and has been used in sensors and ultrasound transducers.