Thread by @ProfRachelGaN

Continuing posting #SomeNiceThings... And this really is lovely science. I'll try to explain...

In a ferroelectric the positions of positive and negative charges don't balance one another, so there are internal electric fields within each unit cell (tiny repeat unit) of the material.

Now the thing that defines a ferroelectric is not just the non balancing charges, but the fact that the direction of the field can be in different directions within the crystal.

In a small region, all the unit cells have their field pointing the same way. That region is called a domain. In an adjacent bit of the crystal, the field will point in a different direction. The boundary between the two regions is a domain wall.

Using an external electric field, you can make domains whose internal fields line up roughly with the external field grow, while other domains shrink. This happens by the domain walls moving.

In the post I retweeted, they have actually taken a video of a domain wall moving through a crystal. Isn't that amazing? Let me know if you want to know how they did it, and if so I'll try and explain the technique they're using! But tomorrow...