engineering question #5198
Eman, a 17 year old male from Edmonton asks on February 22, 2011,Q:
Is there any `accessible` natural or man made material that contracts when electricity is introduced?
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There are two classes of materials that contract when a voltage is put across them: reverse piezoelectric materials and electrostrictive materials.
Reverse piezoelectric materials will contract -- though only by about 0.1% -- when a voltage is put across them. Barium titanate, lead titanate, and lead zirconate titanate are examples of such materials. If you wanted to get hold of a sample of such a material, a piezo-electric loudspeaker or a piezo-electric cigarette lighter might be the best place to find one. Barium titanate is also used in some high-capacitance capacitors. It can be purchased via the Web at 41 for 250 grams, though the price drops to 21/kg if you're going to buy a ton or more.
Electrostriction is a similar effect, found in all non-conducting solids but very slight in most of them. A few substances -- lead magnesium niobate, lead magnesium niobate-lead titanate and lead lanthanum zirconate titanate -- exhibit it to a higher degree, but still only about 0.1%. I have found lead magnesium niobate available on the Web at 282 for 25 grams, so it's a lot less accessible than barium titanate.