# Do piezo materials change volume?

I know that piezoelectric materials change shape when voltage is applied to them,but do they also change volume? Do they keep same volume and just change their geometrical shape,or do they also increase or decrease in volume?

I specificaly have in mind PVDF polymer and PZT ceramic.

Yes, they do. The piezoelectric modulus $D_{33}$ is the quantity which describes exactly this effect.