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.

Lead-free piezoelectric (1 − x)(Bi, Na)TiO3–xBaTiO3 (x = 0.06–1.0) thin films were deposited, and their crystal structures, ferroelectricity, and piezoelectric properties were studied. These films were epitaxially grown on SrRuO3 covered (100) SrTiO3 substrates by pulsed laser deposition using ceramic targets. For all the compositions, the tetragonal films were found to be grown with (001), polar-axis orientation, mainly due to the thermal strain caused by the different thermal expansion coefficients between the substrate and films. Tetragonal films with x = 0.3 and 0.5 showed higher tetragonality, c/a ratio, than the reported values for the bulk ceramics due to the clamp of the in-plane a-axis by underlying SrRuO3 lattice. Here, a and c are the lattice parameters along in-plane and out-of-plane directions, respectively. This larger c/a ratio results in higher Curie temperature. It was revealed that remanent polarization and coercive electric field correlate with the increase in the c/a ratio of the films. The film with x = 0.06 exhibits the maximum piezoelectric property.

TiO 3 0.9BaTiO 3 thin films were deposited by pulsed laser deposition as a candidate of lead-free thin films with a positive temperature coefficient of resistance for micro-thermistor applications in microelectro mechanical system devices. ( 001)-oriented epitaxial tetragonal films with a unity (Bi + Na + Ba)/Ti ratio were grown at 675°C under a total pressure of 50 mTorr. The obtained films showed improved insulating properties and clear ferroelectricity. The Curie temperature was estimated to be 200°C by the high-temperature X-ray diffraction measurement, which was almost the same as the reported value for the ceramic.

(100)/(001)-oriented tetragonal Pb(Zr,Ti)O3 films with different thickness of 400 nm, 1000 nm, 1700 nm and 2000 nm were epitaxially grown on (100) c SrRuO3//(100)Pt//(100)ZrO2//Si(100) substrates by pulsed laser deposition. Their ferroelectric and piezoelectric properties were investigated by polarization-electric field and strain-electric field measurements with increasing maximum strength of an applied electric field in a triangular wave. The macroscopic piezoelectric response was quantitatively analyzed with respect to intrinsic and extrinsic contributions based on in-situ X-ray diffraction results under an electric field. The domain switching from (100)- to (001)-oriented domain and the out-of-plane lattice compression in (100)-oriented domain were clearly observed under an electric field, while the out-of-plane lattice deformation of (100)-oriented domain was negligibly small. Furthermore, effective piezoelectric response due to domain switching increased with increasing the film thickness, which is attributed to the decrease of the constraint with increasing film thickness imposed by the substrate.

Ferroelectric thin films are important because of their great potential for use in various electric devices such as ferroelectric random-access memory. It was expected that Bi2SiO5, a Si-containing ferroelectric material, would show improved ferroelectricity by targeting a film with the (001)-orientation (polar-axis) on the substrate. Although there was a narrow process window for the deposition of the (010)/(001)-oriented Bi2SiO5 thin film, it was successfully prepared on a (101)-oriented TiO2 single substrate using the pulsed layer deposition technique. The optimum film deposition conditions and film thickness were found, and in this material, the volume fraction of the (001)-oriented domain reached about 70%. By controlling film orientation to the polar axis, the remanent polarization value of this film was 4.8 μC cm−2, which is the highest value among reported Bi2SiO5.