Giant strain and compling effects of relaxor/ferroelectric lead-free composite piezoceramics

A lead-free relaxor (RE)/ferroelectric (FE) 0-3 composite was developed with a giant strain that resulted from the electric-field-induced ergodic relaxor-to-ferroelectric phase transition at a relatively low operational field of 4 kV mm-1. The composite comprised of 70 vol.% 0.91Bi1/2Na1/2TiO3-0.06BaTiO3-0.03AgNbO3 RE matrix and 30 vol.% 0.93Bi1/2Na1/2TiO3- 0.07BaTiO3 FE seed shows a normalized strain, d_33^*, of 824 pm V-1 at room temperature. In order to explore the underlying mechanism of this composite effect, two multilayer ceramics with alternating RE and FE layers are also prepared, one with the layers parallel (PCM, polarization coupled multilayer) and the other with the layers perpendicular (SCM, strain coupled multilayer) to the electroded surfaces. It is found that in addition to polarization coupling, the strain coupling effect also plays a critical role in the reduction of the RE to FE phase transition field.