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I am trying to understand the differences in the strains produced in piezoelectric materials and magnetostrictive materials.

Magnetostrictive materials will tend to strain the same way along the direction of an applied magnetic field, either stretching or compressing, independent of whether the field is positive or negative in direction, until they reach saturation. This due to a shift/rotation of the magnetic moments rotating the domains and wall physically adjusting the structure as it happens.

With piezoelectric materials if the electric field is applied one way to the crystal it may stretch, but if the field is reversed it will compress. Again the structure is adjusted with a dielectric displacement in response to the field. Looking at the strain/electric field curves there is a point where the applied reverse field will cause the material to change its strain direction. However I think that the fields required for this are probably larger than for any practical application.

I would like to understand why there is this difference, with one material type straining the same way irrespective of the direction of the applied actuating field and the other will change its strain direction with the field?

I imagine it may be to do with the material structures themselves, and how readily they can respond and shift parts of its structure. Like the magnetic moments may be capable of moving more freely compared with the non-centric crystal structures of the piezoelectric that creates the electric dipole.

Aside: Out of curiosity, magnetostrictive materials are typically characterised by their saturation strain, however this does not appear to be the case for piezoelectric materials, I am interested in what may be the saturation strains for piezoelectric materials, and why maximum strains are typically not a characterisation feature for these materials. The usually practise is the dxx values to translate strain in a direction for an applied field, but what are the upper limits of this?

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