Daisuke Kan

Abstract The discovery of a universal behavior in rare‐earth (RE)‐substituted perovskite BiFeO 3 is reported. The structural transition from the ferroelectric rhombohedral phase to an orthorhombic phase exhibiting a double‐polarization hysteresis loop and substantially enhanced electromechanical properties is found to occur independent of the RE dopant species. The structural transition can be universally achieved by controlling the average ionic radius of the A‐site cation. Using calculations b

Here, the authors clarify the physical origin of anomalies in transverse resistivity often observed in exotic materials, such as SrRuO${}_{3}$, where the Berry curvature is manifested in transport properties. Their thorough magnetotransport investigations and model formulations reveal that the previously attributed mechanism for the anomalies -- the topological Hall effect -- is not the only interpretation. They show that inhomogeneous magnetoelectric properties in the oxide, namely the coexiste

Blue-light emissions from electron-doped SrTiO3 single crystals at room temperature were observed. Substituting La3+ for Sr2+ and Nb5+ for Ti4+ in SrTiO3 provides electron carriers in Ti 3d conduction bands; these carriers are responsible for the room-temperature blue-light emission. This blue-light emission is essentially the same as that observed in Ar+-irradiated oxygen-deficient SrTiO3. This blue luminescence is independent of the defect type. The chemical substitution of La3+ for Sr2+ chang

Chemical substitution-induced continuous ferroelectric polarization rotation in BiFeO3 is discovered. Rare-earth-substituted BiFeO3 is a unique system in which the ferroelectric polarization vector continuously rotates, and by controlling the composition via substitution, a particular direction of the polarization vector may be ‘dialled up’ with an arbitrary angle between the [111] and [001] directions.

We report on our characterization of the structural, electrical, and magnetic properties of tetragonal SrRuO3 (SRO) thin films stabilized under both compressive and tensile strain. These tetragonal films consisting of the deformed RuO6 octahedra without rotations were coherently grown on (110)ortho NdGaO3 and (110)ortho GdScO3 substrates, which provide compressive (−1.7%) and tensile (+1.0%) strains, respectively. The ferromagnetic transition temperature TC for the compressively strained film is

Abstract Thickness‐dependent structure–property relationships in strained SrRuO 3 thin films on GdScO 3 (GSO) substrates are reported. The film is found to have epitaxially stabilized crystal structures that vary with the film thickness. Below 16 nm, the √2 a pc × √2 a pc × 2 a pc monoclinic structure is stabilized while above 16 nm the film has the a pc × 2 a pc × a pc tetragonal structure. The thickness‐dependent structural changes are ascribed to the substrate‐induced modification in the RuO

We investigated effects of the laser fluence on structural and ferroelectric properties in BaTiO3 epitaxial thin films grown by pulsed laser deposition. We find that the low laser fluence causes the cation non-stoichiometry in the films. X-ray diffraction and ferroelectric hysteresis loop measurements reveal the strong impacts of the fluence-dependent cation non-stoichiometry on the structural and ferroelectric properties of the films. The ferroelectricity is observed for the films grown with th

Detailed structural investigations on the substitution-induced structural phase transition from the rhombohedral phase to an orthorhombic phase in (Bi,RE)FeO3 epitaxial thin films (RE = La, Sm, and Dy) grown on (100) SrTiO3 substrates are presented. X ray diffraction reveals that the unit cell dimensions of the orthorhombic phase are strongly dependent on the type of the RE dopant. For RE = La3+ ion, which has an ionic size comparable to the Bi3+ ion, the unit cell is found to be a0 × a0 × 2a0,

We have investigated detailed structural properties of epitaxial BiFeO3 thin films grown on (001), (110), and (111) SrTiO3 substrates in thicknesses up to 1 μm. X-ray reciprocal space mappings reveal that the fabricated films have crystal structures and the strain relaxation dictated by the substrate orientation. The rhombohedral structure, which is observed in the bulk form, is maintained only when the film is grown on the (111)-oriented substrate. The films grown on the (001) and (110)-oriente

Abstract The recovery of a modulated magnetic structure in epitaxial BiFeO 3 thin films as revealed by neutron diffraction is reported. The magnetic structure in thin films is found to strongly depend on substrate orientation. The substrate orientation causes different strain–relaxation processes resulting in different thin‐film crystal structures. The (110) oriented film with a monoclinic structural phase has a single‐domain modulated magnetic structure where the magnetic moment lies in the HHL

Oxygen reduction reaction (ORR) catalytic activity of La0.67Sr0.33MnO3 epitaxial thin films was investigated in a KOH solution by using a rotating-disk electrode. We found that while the films exhibit ORR current, the current is not limited by oxygen transport resulting from the film electrode rotation and shows the large hysteresis against the potential sweep direction. This behavior is in stark contrast to the oxygen reduction reaction activity of an electrode ink made from LSMO bulk powder, w

Hydrogen spillover is a phenomenon in which hydrogen atoms generated on metal catalysts diffuse onto catalyst supports. This phenomenon offers reaction routes for functional materials. However, due to difficulties in visualizing hydrogen, the fundamental nature of the phenomenon, such as how far hydrogen diffuses, has not been well understood. Here, in this study, we fabricated catalytic model systems based on Pd-loaded SrFeO<i>_x</i> (<i>x</i> ∼ 2.8) epitaxial films and investigated h