Phase‐Field Study of Electromechanical Coupling in Lead‐Free Relaxor/Ferroelectric‐Layered Composites

The interface coupling effect of multilayer lead‐free ceramic/ceramic relaxor/ferroelectric composites is studied by finite element–based phase‐field simulations. The macroscopic electromechanical behavior of such composite systems is influenced by both polarization and strain coupling through the electrical and mechanical interaction of connected layers. Separating such interconnected phenomena is difficult experimentally. Here, we direct investigate different coupling effect by introducing soft and charge interphase layers in the serial‐type layer composite model. The large strain response of the composite results from the electric field–induced nonpolar–polar phase transition of the relaxor constituent. A new relaxor phase‐field model is first developed to reproduce this phase transition and parameterized by fitting the measured hysteresis loops. It is then directly compared to the experimental results of the serial‐type composite composed of 0.91Bi 1/2 Na 1/2 TiO 3 –0.06BaTiO 3 –0.03AgNbO 3 and 0.93Bi 1/2 Na 1/2 TiO 3 –0.07BaTiO 3 . Results show that the lateral strain coupling in the serial layer contributes considerably to the large signal piezoelectric coefficient . The primary enhancement in is due a reduction in the remanent strain of the ferroelectric layer caused by the lateral mismatch. Moreover, charge interphase layers in the composite can introduce an internal electric field, leading to a weaker large‐signal response compared with the composite with coherent interfaces.