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Q & A: PLZT

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Most recent answer: 10/06/2009
Q:
Please tell me about some special properties of plzt ceramics.
- Mridula
India
A:
Odd you should ask that question, since it's about one of the few materials issues I happen to have worked on. PLZT (Lead zirconium titanate, doped with a little lanthanum) is what's called a relaxor ferroelectric. In simple ferroelectrics, the atoms displace a little from the positions they take in the simple crystal found at high temperatures. They settle in with the positively charged atoms shifted a little one way and the negative ones shifted the other way, on average. That makes a big electric field.
In relaxors the disordered positions of the atoms (e.g. where the lanthanums happen to land) somehow cause that ferroelectric effect to break into rather small regions with the displacements pointing different directions. These small regions realign pretty easily when an external field is applied. That means that the internal field responds very much to an external field. The 'dielectric constant' describing that response is huge- say 10,000, as compared to around 10 for common materials.
The dimensions of the crystal along the direction of its internal field and along the other directions aren't exactly the same, since the crystal stretches a little as the atoms move to their displaced positions. That means that when you change the directions with an external field, the shape of the crystal changes- the 'piezoelectric effect'. Likewise, when you squeeze the crystal, if it has already had its displacements partly lined up, the net displacement changes so you get an electrical voltage on it. PLZT is very piezoelectric when it's partly aligned, so it's very useful for making sensors that give a voltage in response to mechanical strain, or that move a little in response to a voltage.

Mike W.

(published on 10/22/2007)

Follow-Up #1: buying PLZT

Q:
Could you suggest a few vendors for PLZT material? Thank you very much.
- Tim
Canada
A:
We used samples made by a collaborator. I think you can find vendors by searching for "piezoelectric" materials, perhaps "piezoelectric ceramics".

Mike W.

(published on 10/06/2009)

Follow-up on this answer.