Multilayer lead‐free piezoceramic composites: Influence of co‐firing on microstructure and electromechanical behavior

Abstract

In this study lead-free 2-2 and 0-3 ceramic/ceramic composites comprised of the non-ergodic relaxor 0.93(Bi 1/2 Na 1/2 )TiO 3 -0.07BaTiO 3 and ergodic relaxor 0.94Bi 0.5 (Na 0.75 K 0.25 ) 0.5 TiO 3 -0.06BiAlO 3 were investigated. The macroscopic electromechanical behavior was characterized as a function of continuent content, revealing an enhancement in the unipolar strain from the multilayer composite structure. Systematic evaluation of the effects of co-sintering on microstructural properties, such as grain size and porosity, revealed potential mechanisms by which the increase in unipolar strain was achieved. In addition, interdiffusion between the constituents was observed, providing evidence for the formation of a functionally graded ceramic by co-sintering. These data are contrasted with highresolution energy dispersive X-ray microanalysis for measurement of chemical composition across the interface of 2-2 ceramics. These findings provide insight into how synthesis routes can be optimized for tailoring the enhancement of electromechanical properties of lead-free electroceramic composite systems. K E Y W O R D S composites, ferroelectricity/ferroelectric materials, laminates, piezoelectric materials/properties, sinter/ sintering

Investigating the importance of strain-coupling in lead-free 2–2 relaxor/ferroelectric composites with digital image correlation

“…For instance, as pores have a relative permittivity of 1, charge accumulation during the application of an electric field can occur at the interface between the pore and the FE, resulting in a localized large electric field. As a result, the bilayer composition of NBT-7BT with 20 vol% 0.94Bi 0.5 (Na 0.75 K 0.25 )0.5TiO 3 -0.06BiAlO 3 showed the highest increase in pore size and therefore also the highest strain response as shown by Ayrikyan et al [32].…”

“…Even though composites have demonstrated promising results, the underlying mechanisms are still not fully understood, such as the internal residual stresses and porosity arising from different sintering trajectories of the end members, interdiffusion between the constituents, and the influence of strain coupling. For this reason, studies on 2-2 composites have been conducted on different material systems to highlight certain aspects [32][33][34][35]. In particular, the work by Zhang et al [35] showed the importance of strain-coupling in multilayer composites of 0.91(Na 1/2 Bi 1/2 )TiO 3 -0.06BaTiO 3 -0.03AgNbO 3 and NBT-7BT by varying the orientation of the interfaces parallel and perpendicular to the applied electric field, where it was possible to remove the influence of the polarization coupling (PC).…”

“…Further studies also showed that the interdiffusion between the constituent materials can change with the volume fraction of the seed material, as well as the stresses during sintering and the resulting residual stress. These changes at the interface can have an overall impact on the composite, as it changes the mechanical properties around the interface, together with increased pore fraction, increased grain size, and changes to the crystallographic structure [32,33]. For instance, as pores have a relative permittivity of 1, charge accumulation during the application of an electric field can occur at the interface between the pore and the FE, resulting in a localized large electric field.…”

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

“…Studies that further differentiate the contribution of lateral strain coupling from the polarization coupling would be helpful. More recent work has also found that internal stresses due to different sintering shrinkages and thermal expansions between constituents can result in changes in microstructure and porosity, which are also expected to affect the electromechanical properties. The interface between the constituents can weaken both the mechanical and polarization coupling.…”

“…[16] To decouple these effects in 0-3 composites is challenging, making the determination of their relative contributions nontrivial. More recent work has also found that internal stresses due to different sintering shrinkages and thermal expansions between constituents can result in changes in microstructure and porosity, [18] which are also expected to affect the electromechanical properties. In the parallel case, the strain in the poling direction is coupled through the interface, while in the perpendicular case, the polarization charge is coupled.…”