Ichiro Fujii

Electric field induced lattice strain in pseudocubic Bi(Mg1/2Ti1/2)O3-modified BaTiO3-BiFeO3 piezoelectric ceramics

Contributions to the piezoelectric response in pseudocubic 0.3BaTiO3-0.1Bi(Mg1/2Ti1/2)O3-0.6BiFeO3 ceramics were investigated by synchrotron X-ray diffraction under electric fields. All of the lattice strain determined from the 110, 111, and 200 pseudocubic diffraction peaks showed similar lattice strain hysteresis that was comparable to the bulk butterfly-like strain curve. It was suggested that the hysteresis of the lattice strain and the lack of anisotropy were related to the complex domain structure and the phase boundary composition.

Fabrication of (K,Na)NbO3 films on SrRuO3/(001)SrTiO3 substrates by pulsed laser deposition

1–3-µm-thick (K,Na)NbO3 films were epitaxially grown on SrRuO3/(001)SrTiO3 substrates by the pulsed laser deposition using (KxNa1−x)NbO3 targets. Energy dispersive X-ray spectroscopy analysis showed that the film K content was about 10% lower than the target K content x at x = 0.1–0.8, and the (K + Na)/Nb atomic ratio was 0.8–1.0. Reciprocal space mapping of the films revealed that the films were epitaxially grown at x = 0–0.7, and the crystal system was altered with increasing K content. Ferroelectric polarization–electric field loops were observed at x = 0–0.9, with the maximum remanent polarization of ~40 µC/cm2 at x = 0.5. The remanent polarization vs K content profile was discussed with crystal structure analyses.

Ferroelectric properties of (Li,K,Na)NbO3 epitaxial films fabricated by pulsed laser deposition

(LixK0.1Na0.9−x)NbO3 (x = 0, 0.05, 0.1, and 0.2) epitaxial films were prepared by pulsed laser deposition on SrRuO3/(001)SrTiO3 substrates. Reciprocal space mapping indicated that the crystal systems of the films were antiferroelectric orthorhombic at x = 0, antiferroelectric orthorhombic and/or ferroelectric monoclinic depending on film thickness at x = 0.05, ferroelectric monoclinic at x = 0.1, and ferroelectric rhombohedral at x = 0.2. Polarization–electric field responses were ferroelectric for all the films. At x = 0.05, the remanent polarization was maximized to ~35 µC/cm2, which was more than four times larger than that at x = 0. This was probably due to a stabilized monoclinic phase under a high electric field.

Domain structures of (Li,Na)NbO3 epitaxial films

The domain structures of (LixNa1-x)NbO3 (xu2009=u20090, 0.05, 0.10, and 0.13) epitaxial films on SrRuO3/(001) SrTiO3 substrates were studied by laser scanning microscopy and reciprocal space mapping. The stripe domains with in-plane antiferroelectric polarization of an orthorhombic P phase were observed at xu2009=u20090. At xu2009=u20090.05 and 0.10, the crystal phase was changed to an orthorhombic Q phase and the domain structure was changed to a mixture of stripe domains with in-plane ferroelectric polarization and thick line-like domains with out-of-plane ferroelectric polarization. At xu2009=u20090.13, the line-like domain pattern was altered to a leaf-like domain pattern and out-of-plane ferroelectric polarization of a rhombohedral N phase was induced in the stripe domains. After an electric field was applied along an out-of-plane direction, some of the stripe domains with the in-plane polarization of the P phase at xu2009=u20090 and those with the in-plane polarization of the Q phase at xu2009=u20090.05 were switched to domains with out-of-plane ...

Piezoelectric and Dielectric Enhancement of New Nano-structured Ceramics with Heteroepitaxial Interfaces

Barium titanate (BT) - potassium niobate (KN) nano-structured ceramics with an artificial morphotropic phase boundary (MPB) structure were prepared by a solvothermal method at temperatures below 230 °C. Various characterizations of the BT-KN nano-structured ceramics revealed that the BT/KN molar ratio was 1, the porosity was around 30 %, and the interface between BT particles and KN crystals was heteroepitaxial. The apparent piezoelectric constant d33* was 136 pC/N, which was three times larger than that of 0.5BT-0.5KN dense composite ceramics. The concept proposed in this study can be useful to create piezoelectric ceramics with artificial MPB regions.

Fabrication of lead-free ferroelectric (Na,K)NbO 3 thin films by pulsed laser deposition

We fabricated (Na1-xKx)NbO3 (NKN) thin films with x=0.1 (NKN10), 0.2 (NKN20) and 0.3 (NKN30) on SrTiO3 (STO) substrate by pulsed laser deposition (PLD). NKN ceramics were prepared by modified solid-state reaction method, and NKN thin films were fabricated using this ceramics target by PLD. The NKN films were epitaxially grown on (001), (110) and (111) STO substrates. The NKN films on (001) STO had a smooth surface, the films on (110) STO had a striped pattern, and the films on (111) STO had trigonal pyramid-like structure. It was observed that remanent polarizations of the films increased with increasing K content. The P-E hysteresis of NKN30 film on (111) STO substrate showed a very large hysteresis loop with a remanent polarization Pr of 69 μC/cm2.

Laser scanning microscopy observation of domain switching in NaNbO 3 epitaxial film

Domain patterns of a 001-oriented NaNbO3 film prepared on a SrRuO3/(001)SrTiO3 (STO) substrate were observed by laser scanning microscopy during the application of the ac electric field amplitude of 100 kV/cm. The domain patterns consisted of vertical and horizontal stripes along the [100] and [010] directions of the (001) STO substrate and slanted stripes along the [110] and [1-10] directions. Only the slanted domain patterns changed with the electric field. When the electric field decreased from +100 kV/cm to -100 kV/cm, some slanted domain patterns shrank in the stripe direction and completely disappeared near the coercive field, and then reappeared and expanded in the stripe direction upon further decrease of the electric field while other domain patterns just shrank and expanded in the stripe direction without disappearance. These results suggested two kinds of domain switching route in the 001-oriented NaNbO3 thin film.

(Ag,Li)NbO 3 thin films fabricated on (001), (110), and (111)SrTiO 3 substrates by pulsed laser deposition

001-, 110-, 111-oriented (Ag_1-xLi_x)NbO₃ (ALN) films with x=0.05 (ALN05), 0.1 (ALN10), and 0.15 (ALN15) were fabricated on (001), (110) and (111) SrTiO₃ (STO) substrates by pulse laser deposition (PLD). The surface texture of the ALN films ware dependent on the crystal orientation of STO substrates. All the ALN films exhibited a ferroelectric behavior. The ALN films with x=0.1 deposited on (111) STO showed the largest remanent polarization of 40μC/cm².