Progress in engineering high strain lead-free piezoelectric ceramics

Abstract

Environmental concerns are strongly driving the need to replace the lead-based piezoelectric materials currently employed as multilayer actuators. The current review describes both compositional and structural engineering approaches to achieve enhanced piezoelectric properties in lead-free materials. The review of the compositional engineering approach focuses on compositional tuning of the properties and phase behavior in three promising families of lead-free perovskite ferroelectrics: the titanate, alkaline niobate and bismuth perovskites and their solid solutions. The 'structural engineering' approaches focus instead on optimization of microstructural features including grain size, grain orientation or texture, ferroelectric domain size and electrical bias field as potential paths to induce large piezoelectric properties in lead-free piezoceramics. It is suggested that a combination of both compositional and novel structural engineering approaches will be required in order to realize viable lead-free alternatives to current lead-based materials for piezoelectric actuator applications.

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…The last seven decades of research on ferroelectrics yielded strategies to enhance strain mechanisms 150,151 , as displayed in Figure 2.15. To date, compositional engineering remains the preferred approach, although structural engineering has also led to technologically relevant achievements.…”

“…To date, compositional engineering remains the preferred approach, although structural engineering has also led to technologically relevant achievements. 150 The strategies in white modify both intrinsic and extrinsic contributions to the piezoelectric activity, while those in light blue modify mostly the extrinsic contributions. Note that other approaches not directly related to the modification of material parameters can also be employed to enhance electromechanical properties.…”

“…153 Considerable research has been performed in BT-based materials or KNN-based materials characterized by presence of PPBs. 29,150,154 Alternatively, research has also focused considerably on systems with presence of a MPB-like ‡ ‡ transition such as in lead-based piezoelectrics or in some BNT-based materials. 10,29,150,151,154,155 The origin of maximized properties at interferroelectric phase boundaries has been commonly attributed to a FD transverse instability of that ease its reorientation due to increased multiplicity of polarization states, reduced free energy anisotropy, and softening of the crystal lattice.…”

“…29,150,154 Alternatively, research has also focused considerably on systems with presence of a MPB-like ‡ ‡ transition such as in lead-based piezoelectrics or in some BNT-based materials. 10,29,150,151,154,155 The origin of maximized properties at interferroelectric phase boundaries has been commonly attributed to a FD transverse instability of that ease its reorientation due to increased multiplicity of polarization states, reduced free energy anisotropy, and softening of the crystal lattice. 42,150,[156][157][158][159][160] Transverse instabilities have been pointed out in several works as the key for the enhancement of dielectric and electromechanical properties.…”

Additively‐manufactured piezoelectric devices

“…Other devices, such as flexoelectric, truncated pyramids [11] or flextensional transducers [29] can also be built without the same heavy restrictions on geometry that have always been imposed on their construction. Lead-free piezoelectric materials where the piezoelectric coefficients are generally inferior to those of lead-based materials can be built with structures that enhance their functional properties for specific applications [30]. With the adoption of this low-cost technology, the ability to create complex functional devices can be available as a standard laboratory tool for all material scientists and engineers.…”