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.

This report describes the development of a solution-assisted, polymer-free transfer method and the characterization of chemical vapor deposition (CVD)-grown graphene on hexagonal boron nitride. Raman analysis reveals that polymer-free samples have small variations in G- and 2D-mode Raman frequencies and are minimally affected by charge doping as observed for clean exfoliated graphene. Electrical measurements indicate that charge doping, hysteresis, and carrier scattering are suppressed in polymer-free samples. The results demonstrate that this method provides a simple and effective way to prepare clean heterostructures of CVD-grown, large-area graphene and other two-dimensional materials.

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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.