Large Piezoelectric Response in Lead-Free (Bi_0.5Na_0.5)TiO₃-Based Perovskite Thin Films by Ferroelastic Domain Switching: Beyond the Morphotropic Phase Boundary Paradigm

Abstract

Strong electromechanical coupling is observed in tetragonal Pb-free 0.7(Bi 0.5 Na 0.5 )-TiO 3 -0.3BaTiO 3 films, which is far from the morphotropic phase boundary, prepared by pulsed laser deposition on a Si substrate. The tensile strain induced during cooling causes in-plane polarization in an oriented film on a Si substrate, while an epitaxial film grown on a SrTiO 3 substrate exhibits out-ofplane polarization. S−E curve analysis reveals that the obtained piezoelectric coefficient for the film on the Si substrate (d 33,f ≈ 275 pm/V) is approximately eight times higher than that for the epitaxial film on the SrTiO 3 substrate (d 33,f ≈ 34 pm/V). In situ X-ray diffraction analysis confirms the occurrence of domain switching under an electric field from in-plane to out-of-plane polarization. An effective piezoelectric stress coefficient, e 31,eff , of ∼19 C/m 2 is obtained from a Si cantilever sample, which is the highest among the reported values for Pb-free piezoelectric films and is comparable to those for Pb-based films. The significant piezoelectric response produced by domain switching in the Pb-free materials with the composition far from the morphotropic phase boundary will expand future applications due to their both outstanding properties and environmental sustainability.

Achieving High Piezoelectric Performance across a Wide Composition Range in Tetragonal (Bi,Na)TiO3–BaTiO3 Films for Micro-electromechanical Systems

“…Owing to the large thicknesses of the films, the misfit strains are considered to be almost relaxed during film deposition, which is introduced by the difference in the lattice parameters between the film and the substrate. , Shimizu et al explained that the release of tensile strain accumulated during cooling after deposition at the Curie temperature resulted in the formation of BNT-BT films with a -domain dominant structures having both a - and c -axes along the in-plane direction deposited on a Si substrate with a low thermal expansion coefficient. , In contrast, compressive strain is generated upon cooling below T C after film deposition, mainly owing to expansion in the c -axis domain structure along the in-plane direction. This strain is relieved by an increase in the domain wall owing to an external force, such as the application of an electric field, and P r , namely, the out-of-plane polarization component, increases as shown in Figure (d).…”

“…The estimated volume fraction of the c -domain was approximately 33% under the electric field, as shown in Figure S6 and Table S1. On the basis of this change in the volume fraction, d 33,f ≈ 152 pm/V was calculated using the following equation d 33 , f = { c × V c + a × false( 1 − V c false) } − { c 0 × V c 0 + a 0 × false( 1 − V c 0 false) } a 0 × ( 1 − V c 0 ) + c 0 × V c 0 × 1 E where E , V c , c , and a represent the electric field, c -domain volume fraction, c -axis lattice parameter, and a -axis lattice parameter, respectively. The subscript “0” denotes no application of an electric field.…”

Ultrahigh Ferroelectric and Piezoelectric Properties in BiFeO3–BaTiO3 Epitaxial Films Near Morphotropic Phase Boundary

“…Comparison of ferroelectric and piezoelectric properties of the BF–BT films in this study with (Bi x Na 1– x )­TiO 3 (BNT)-based, − (K x Na 1– x )­NbO 3 (KNN)-based, − BFO-based, ,, and lead-based , materials systems. Different systems are represented by symbols of different colors.…”

Recent Progress on Structure Manipulation of Poly(vinylidene fluoride)‐Based Ferroelectric Polymers for Enhanced Piezoelectricity and Applications

“…Based on the inverse piezoelectric effect, the piezoelectric coefficient can be obtained by measuring the strain (S) curves as a function of the electric field (E). [47] The working mechanism of this method is shown in Figure 5e, [48] where a voltage generator applies an electric field to the piezoelectric material, and then the induced strain is detected by a high-resolution displacement sensor, such as the photonic sensor (or called Fotonic sensor, MTI optical fiber measurement system, fiber-optic probe), [48][49][50] laser displacement sensor (or called laser Doppler vibrometers), [51,52] and linear variable differential transformer (LVDT). [29,53] Generally, two different inverse piezoelectric coefficients are obtained from the S-E loops, i.e., the d ij calculated as the slope the S-E loops at low electric fields (below the coercive field, E c ), [30,36] and the largesignal d ij * measured at high electric fields using the equation, [47] d ij * = S max /E max , where S max and E max are the maximum strain and the maximum electric field, respectively.…”