Giant electric-field-induced strain by new mechanism

- New horizon for environmental-friendly high-performance piezoelectrics-

Piezoelectricity is a unique effect that certain crystals (called ferroelectrics) can swell or shrink when applied with voltage or conversely generate an electric voltage when applying a stress.

Ferroelectric crystals are characterized by their asymmetric or polar structures. In electric field, ions undergo asymmetric displacement and result in a small change in crystal dimension, which is proportional to the applied field　(Fig.1a). This effect has for decades found wide applications ranging from telephone speaker to naval sonar. However, the effect is normally very small (mostly in the order of 0.01% change in shape at a electric field of 100V/mm) and thus this has limited the range of its applications.

Very recently we discovered a “giant” electric-field-induced shape-change in lightly Fe-doped BaTiO₃ crystals by utilizing a new mechanism (Fig.1b). This giant electro-strain stems from an unusual reversible domain switching (most importantly the switching of non-180^o domains) in which the restoring force is provided by a general symmetry-conforming property of point defects.

Fig.2 shows that an aged lightly Fe-doped BaTiO₃ single crystal can generate a large recoverable non-linear strain of 0.75% at a low field of 200V/mm. At the same field this value is about 40 times higher than piezoelectric PZT ceramics and more than 10 times higher than the high strain PZN-PT single crystals.

This mechanism provides a general method to achieve large electro-strain effect in a wide range of ferroelectric systems and the effect may lead to novel applications in ultra large stroke and non-linear actuators.

Another important significance of this work is the possibility of utilizing the new mechanism to create high-performance electro-strain materials based on Pb-free compounds, avoiding the environmental hazard caused by PZT.

See X. Ren, Nature Materials,3, 91-94 for details.