Relaxor/Ferroelectric Composites: A Solution in the Quest for Practically Viable Lead‐Free Incipient Piezoceramics

Abstract

Recently developed lead‐free incipient piezoceramics are promising candidates for off‐resonance actuator applications with their exceptionally large electromechanical strains. Their commercialization currently faces two major challenges: high electric field required for activating the large strains and large strain hysteresis. It is demonstrated that design of a relaxor/ferroelectric composite provides a highly effective way to resolve both challenges. Experimental results in conjunction with numerical simulations provide key parameters for the development of viable incipient piezoceramics.

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…242 Differences in polarization gradients between core and shell should lead to a higher electric field in the shell, thereby enabling the electric field induced phase transition at reduced electric fields. 234,236 The ferroelectric state can still be induced at 80 °C and 4 kV/mm ( Figure 5.57 (c) 7 ). Although, considering the lower values in the peak of ( ) at 80 °C compared to room temperature ( Figure 5.43), a lower ferroelectric state fraction and switching processes are expected.…”

“…For this purpose, 0-3 BNT-based composites were designed with a macroscopically polar seed such as a ferroelectric or non-ergodic relaxor state in conjunction with a macroscopically non-polar matrix such as a paraelectric or ergodic relaxor state. [233][234][235][236][237][238][239][240] This approach allowed for an enhanced strain output with reduced hysteresis, which gave between 10 % and 30 % higher electromechanical response than solid solution materials at 4 kV/mm. 233,236 The feasibility of tailoring the temperature and frequency stability with the composite approach was also demonstrated at the expense of reduced strain output.…”

“…[233][234][235][236][237][238][239][240] This approach allowed for an enhanced strain output with reduced hysteresis, which gave between 10 % and 30 % higher electromechanical response than solid solution materials at 4 kV/mm. 233,236 The feasibility of tailoring the temperature and frequency stability with the composite approach was also demonstrated at the expense of reduced strain output. 237 The large signal strain and polarization, as well as the small signal dielectric properties, were calculated successfully in several works based on a model that regarded the microstructural constituents as two capacitors in series.…”

“…237 The large signal strain and polarization, as well as the small signal dielectric properties, were calculated successfully in several works based on a model that regarded the microstructural constituents as two capacitors in series. 234,236,241 Since the charge of two capacitors in series is equal, the applied macroscopic electric field is distributed differently between constituents to assure a constant polarization. Generally, the macroscopically non-polar matrix depicts lower indicating that the electric field on the matrix will be higher.…”

Forced electrostriction by constraining polarization switching enhances the electromechanical strain properties of incipient piezoceramics

“…The expected outcome of this approach is the same as that of the core-shell approach. [10][11][12] One of the most important advantages of this technique is its practical simplicity. However, a problem arises because 0-3 type composites consist of ceramics with similar compositions consolidated at relatively high temperatures.…”