Shintaro Yasui

Shintaro Yasui
Tokyo Institute of Technology | TITech ·  Materials and Structures Laboratory

Doctor of Engineering

About

146
Publications
14,356
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1,538
Citations
Additional affiliations
April 2013 - present
Tokyo Institute of Technology
Position
  • Professor (Assistant)

Publications

Publications (146)
Article
Full-text available
The field-induced strain of microcantilever structured Pb(Zr 0.44 Ti 0.56 )O 3 (PZT) films on Si substrate was observed by a microbeam X-ray diffraction 2-dimensional detector. The observed field-induced strain strongly depended on the thickness of the substrate. The experimentally estimated longitudinal piezoelectric constants ( d 33 ) for PZT fil...
Article
GaFeO 3 -type oxides are promising multiferroic materials due to the coexistence of spontaneous magnetization and ferroelectric polarization properties at room temperature. As these ferroic properties feature a large anisotropy, single crystals are required. However, the magnetization of GaFeO 3 -type single crystals remains low at room temperature...
Article
Full-text available
A crystallographically heterogeneous interface was fabricated by growing hexagonal graphene (Gr) using chemical vapor deposition (CVD) on a tetragonal FePd epitaxial film grown by magnetron sputtering. FePd was alternately arranged with Fe and Pd in the vertical direction, and the outermost surface atom was identified primarily as Fe rather than Pd...
Article
Chimney-ladder sulfide Sr9Ti8S24 (STS) has potential as a thermoelectric (TE) material because of its intrinsic low thermal conductivity. We studied the growth of a polycrystalline STS sample and its fundamental TE properties. The resistivity of n-type polycrystalline STS can be described as thermal activation and the potential barrier at grain bou...
Article
The phase stability, ferroelectricity, and magnetism of highly crystalline epitaxial ε-Fe2O3 films deposited on SrTiO3(111) substrates are reported. Temperature-dependent X-ray diffraction (XRD) measurements revealed that α-Fe2O3 appeared as a secondary phase after samples were annealed up to 1000°C. A clear saturated and opened polarization– elect...
Article
Controlling nanostructures and crystallographic orientations in epitaxial nanocomposite thin films are important for tuning their physical properties. Here, we present epitaxial nanocomposite thin films of (110) oriented CoFe2O4 (CFO) and (1110) oriented Bi5Ti3FeO15 (BTFO15) grown on SrTiO3 (110) substrates with a vertically aligned pillar–matrix t...
Article
High-speed rechargeable Li ion batteries are in strong demand. Two methods have been reported to improve the high-speed rechargeability of electrodes: reducing particle size and introducing a surface support. However, the effectiveness of the latter could not be directly compared among reports due particle size differences from study to study. Our...
Article
We report on excellent electrochemical properties, Li ion diffusion coefficient and work function of Li2MnO3 thin films fabricated by RF sputtering technique. The X-ray diffraction study confirms the formation of Li2MnO3 thin film in layered structure. The X-ray photoelectron spectroscopy (XPS) study confirms the existence of Li and Mn ions and the...
Article
The reactor pressure vessel (RPV) failure timing in Unit 1–3 of the Fukushima Daiichi Nuclear Power Plant was estimated by considering the metallic interactions in the lower plenum. The re-molten core materials could attack and penetrate the weld and, hence, the materials science aspect is expected to provide insights that can assist in the estimat...
Article
We report ultrafast charge transfer along the Li-ion pathway via a dielectric layer at the electrolyte−electrode interface. The rate capabilities of dielectric-modified cathodes were evaluated as a function of the combination of electrolyte solvents and dielectric layers having various dielectric constants, εr. The high-rate capability was enhanced...
Preprint
Full-text available
For the first time, the dielectric response of a BaTiO3 thin film under an AC electric field is investigated using time-resolved X-ray absorption spectroscopy at the Ti K-edge to clarify correlated contributions of each constituent atom on the electronic states. Intensities of the pre-edge eg peak and shoulder structure just below the main edge inc...
Article
Full-text available
For the first time, the dielectric response of a BaTiO3 thin film under an AC electric field is investigated using microsecond time-resolved X-ray absorption spectroscopy at the Ti K-edge in order to clarify correlated contributions of each constituent atom on the electronic states. Intensities of the pre-edge eg peak and shoulder structure just be...
Article
The antiferroelectric (AFE) phase, in which nonpolar and polar states are switchable by an electric field, is a recent discovery in promising multiferroics of hexagonal rare-earth manganites (ferrites), h-RMn(Fe)O3. However, this phase has so far only been observed at 60-160 K, which restricts key investigations into the microstructures and magneto...
Article
GaFeO3-type iron oxides are promising multiferroics due to the coexistence of large spontaneous magnetization and polarization near room temperature. However, the high leakage current and difficulties associated with synthesizing single crystals make it difficult to achieve two important features in the system: a large ferroelectric polarization sw...
Article
In-plane ferroelectric polarization in BaTiO3 (BTO) epitaxial thin films on MgAl2O4(001) (MAO) is reported. The directional dependence of both in-plane polarization curves and Raman spectroscopy shows that the films have an orthorhombic structure at room temperature, in contrast to the tetragonal structure of the corresponding bulk. The largest in-...
Article
Full-text available
Synthetic techniques to prepare large‐size, flexible, and high‐quality single‐crystalline sheets of transition metal oxides are crucial to developing low‐energy consumption devices. One promising way is a lift‐off and transfer technique using a heterostructure of polymer supporting oxide and Sr3Al2O6 (SAO) layers grown on a single‐crystalline subst...
Article
Full-text available
Bent band structures have been empirically described in ferroelectric materials to explain the functioning of recently developed ferroelectric tunneling junction and photovoltaic devices. This report presents experimental evidence for ferroelectric band bending, which was observed in the depth profiles of atomic orbitals of angle-resolved hard x-ra...
Article
We report on band edge parameters calculated from the electrochemical data, work function, Li ion dynamics and excellent electrochemical properties of Li4Ti5O12 thin films prepared by RF sputtering technique. Raman spectra recorded at room temperature confirms the formation of Li4Ti5O12 thin films in spinel structure. Surface morphology and roughne...
Article
A BiFeO3 (BFO) film is epitaxially grown on an (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) substrate to investigate the lattice mismatch effect on the domain structure and lattice strain status within the BFO film. Atomic resolution scanning transmission electron microscope image, selected area electron diffraction (SAED) patterns, and X-ray reciprocal spa...
Article
Zn-deficient spinel-type ZnGa2O4:Mn2+ phosphor thin films were prepared using pulsed laser deposition. With an increase (decrease) in the Zn deficiency (concentration) of the films, changes in lattice constant, optical band gap, and photoluminescence spectra were observed. All films without γ-Ga2O3:Mn showed green luminescence attributable to the t...
Article
We investigated a compositional spread Mn²⁺-doped Zn2SnO4-Mg2SnO4 (Mn-ZMTO) film prepared by combinatorial pulsed laser deposition. The composition of the prepared film gradually changed from Zn2SnO4 (ZTO) to Mg2SnO4 (MTO). Moreover, the lattice constant decreased with an increase in MTO composition. Under ultraviolet irradiation, the film exhibite...
Article
Next-generation nonvolatile memory devices require many functionalities such as high-speed processing, low power consumption, light weight and a simple structure. The use of heterostructures with resistive switching capabilities is a promising way to achieve these functionalities. In this work, the resistive switching characteristics of a newly ide...
Article
ε-Fe2O3, a metastable phase of iron oxide, is widely known as a room-temperature multiferroic material or as a superhard magnet. Element substitution into ε-Fe2O3 has been reported in the literature; however, the substituted ions have a strong site preference depending on their ionic radii and valence. In this study, in order to characterize the cr...
Article
Polar magnets are important materials in fundamental science and technology. However, the requirements for a polar nature are generally incompatible with those for magnetism, and thus there are few polar magnets. At the order and disorder boundaries of cations in ABO3 compounds, two polar ferromagnets of ScFeO3 with polar-corundum-type and LiNbO3-t...
Article
AlxFe2-xO3 (x-AFO) thin films, belonging to the κ-Al2O3 family are interesting because they show room temperature ferrimagnetism and have a polar crystal structure. These class of materials are being studied to observe simultaneous ferrimagnetism and ferroelectricity, and possibility of coupling between the two. However, it is difficult to realise...
Article
Perovskite-type oxynitride BaTaO2N has been attracting attention for its large dielectric constant, which is almost independent of the temperature by measurements on its ceramics. Its dielectric characteristics are attributed to polar nanoregions (PNRs) in the average cubic crystal structure. Polarization saturation to produce a butterfly-like piez...
Article
We previously reported that the BaTiO3(BTO)-LiCoO2(LCO)-electrolyte triple-phase interface (TPI) could play an important role in C-rate enhancement, however, why this supporting material is effective for high performance remains unknown. We focus on the relative permittivity of supporting materials using finite element method calculations and exper...
Article
Full-text available
LiCoO2 (LCO) is one of the most promising cathode materials for Li ion batteries (LIBs). However, LCO shows a rate-limiting step of Li+ migration between electrode and electrolyte interfaces, requiring LIBs to be charged under low-current conditions. For next generation batteries, it will be necessary to meet the demand for a shorter charging-time....
Article
Reversible electric-field induced domain switching in ferroelectric thin films gives rise to a large electromechanical coupling. Despite extensive in situ studies confirming a dominant contribution from domain switching, the speed of the domain wall motion had not been discussed enough. In this study, we performed time-resolved measurement of latti...
Article
RhxFe2−xO3 solid-solution epitaxial thin films were prepared by pulsed laser deposition. The ferroelectricity of Rh0.15Fe1.85O3 thin film was presented by the result of piezoelectric force microscopy phase and amplitude loops measured at room temperature. Ferrimagnetism at room temperature is confirmed by the magnetic hysteresis loop. The coercive...
Article
Full-text available
Lattice mismatch-induced biaxial strain effect on the crystal structure and growth mechanism is investigated for the BiFeO3 films grown on La0.6Sr0.4MnO3/SrTiO3 and YAlO3 substrates. Nano-beam electron diffraction, structure factor calculation and x-ray reciprocal space mapping unambiguously confirm that the crystal structure within both of the BiF...
Preprint
Multiferroic materials open up the possibility to design novel functionality in electronic devices, with low energy consumption. However, there are very few materials that show multiferroicity at room temperature, which is essential to be practically useful. AlxFe2-xO3 (x-AFO) thin films, belonging to the k-Al2O3 family are interesting because they...
Article
High‐quality p‐type chalcostibite CuSbS2 single crystal is successfully synthesized by zone melting method for investigating fundamental properties. The grown crystal is orthorhombic structure and nearly stoichiometric with slightly Cu‐rich composition. The electrical properties are the hole concentration of 8.0 × 10¹⁶ cm⁻³, conductivity of 0.8 S c...
Article
Single-phase multiferroic materials have attracted considerable attention among scientists, due to the strong drive in industry towards device miniaturization, addition of new functionalities, etc. Currently, most of the discovered materials have at-least one ferroic order active only at low temperatures, thereby hindering their induction into prac...
Article
Nanodot BaTiO3 supported LiCoO2 cathode thin films can dramatically improve high-rate chargeability and cyclability. The prepared BaTiO3 nanodot is less than 3 nm in height and 35 nm in diameter, and its coverage is less than 5%. Supported by high dielectric constant materials on the surface of cathode materials, Li ion can intercalate through robu...
Article
Full-text available
κ-Al 2 O 3 -type GaFeO 3 is a promising multiferroic material due to the coexistence of a large spontaneous magnetization and polarization near room temperature. In the current study, we present the magnetic properties of single crystalline GaFeO 3 and compare it with that of ε-Fe 2 O 3 . Magnetic measurements revealed that spontaneous magnetizatio...
Article
Full-text available
A Sol-gel method assisted with spin-coating has been successfully used to grow orthorhombic GaFeO3 epitaxial films on SrTiO3 (111) substrates for the first time. The film with Pna21 crystal structure has been grown along the c-axis. The rocking curve of (004) reflection shows that the Full-Width at Half-Maximum (FWHM) value could be determined to b...
Article
To control the properties of multiferroic materials, substitution of magnetic elements is a useful technique. In this study, we fabricated GaCrxFe1-xO3 and Ga1-yCryFeO3 films by substituting Cr³⁺ (3d³) ions in GaFeO3 for magnetic Fe³⁺ (3d⁵) and nonmagnetic Ga³⁺ (d¹⁰) sites, respectively. The effect of the Cr substitution on the magnetic and dielect...
Article
Lead (Pb)-free perovskite thin films of the ternary BaTiO3–Ba(Mg1/2Ti1/2)O3–BiFeO3 (BT–BMT–BF) solid solution system with preferential crystal orientation were fabricated and the dependence of their polarization behavior on crystal anisotropy was evaluated. The chemical solution deposition (CSD) technique was utilized for the film deposition while...
Article
Full-text available
The recent resurgence of bismuth ferrite (BiFeO3) as a multiferroic material was triggered by the revelation of its true bulk physical properties in the mid 2000s. Subsequently, multiferroic properties of BiFeO3 have been found to improve when it is grown as epitaxial film owing to the biaxial strain imposed by substrate materials. Since the crysta...
Article
Full-text available
The crystal structure of bismuth ferrite (BiFeO3; BFO) epitaxial films was analyzed by X-ray diffraction (XRD) using a two-dimensional detector. The diffraction spots hex (hexagonal notation was used for the rhombohedral structure in this study) specific to the rhombohedral structure (space group: R3c), which clearly separated from the diffractions...
Article
We investigated the thermoelectric properties of high-quality p-type Cu2ZnSnS4 single crystals. This material showed two advantages: low thermal conductivity because of lattice scattering caused by the easily formed Cu/Zn disordered structure, and high conductivity because of high doping from changes to the composition. All samples showed a thermal...
Article
This paper focuses on effects of isovalent La substitution on the crystal structure and dielectric properties of ferroelectric Bi2SiO5. Polycrystalline samples of (Bi1−xLax)2SiO5 are synthesized by crystallization of Bi-Si-O and Bi-La-Si-O glasses with a composition range of 0≤x≤0.1. The crystal structure changes from monoclinic to tetragonal with...
Article
On-board vehicle applications dictate the need for improved low-temperature power densities of rechargeable batteries. Integration of high-permittivity artificial dielectric solid electrolyte interfaces (SEIs) into the lithium ion battery architecture is a promising path to satisfy this need. The relationship between the permittivity of various art...
Article
Lithium ion batteries with high-rate performance have been demanded since electric and hybrid vehicles are released. It is known that high interfacial resistance between electrode and electrolyte prevents intercalation of lithium ions. We investigated high-rate capability of typical LiCoO 2 cathode with various surface morphologies using epitaxial...
Article
We unveil magnetic phases and superconducting transition temperatures (Tc) in an iron-based superconductor with a thick-blocking layer of a perovskite-related transition metal oxide, Sr2VFeAsO3-delta (21113V). 21113V exhibits a superconducting phase in 0.031 =< delta =< 0.145 at temperatures (T) < 37.1 K. Antiferromagnetic (AFM) iron sublattice are...
Article
GaFeO3-type iron oxides are promising multiferroic materials due to the coexistence of a large spontaneous magnetization and polarization near room temperature. However, magnetic substitution, which is a general method to control multiferroic properties, is difficult due to instability of the substituted GaFeO3. In this study, Ga0.5Cr0.5FeO3 epitax...
Article
Ceramic/ceramic composite structures have been proposed as a method for optimizing the electromechanical response of lead-free ferroelectrics. Co-sintering of ceramic composites, however, results in internal residual stresses as well as interdiffusion. In this investigation, the interaction between a nonergodic relaxor ferroelectric 0.93(Bi1/2Na1/2...
Article
Full-text available
We present a comprehensive study of the physical properties of epitaxial cobalt-doped BiFeO3 films ∼50 nm thick grown on (001) LaAlO3 substrates. X-ray diffraction and magnetic characterization demonstrate high quality purely tetragonal-like (T′) phase films with no parasitic impurities. Remarkably, the step-and-terrace film surface morphology can...
Article
Full-text available
Comprehensive crystal structural study is performed for BiFeO3 (BFO) film grown on KTaO3 (KTO) substrate using transmission electron microscopy (TEM) and x-ray diffraction (XRD). Nano-beam electron diffraction (NBED) combined with structure factor calculation and high resolution TEM images clearly reveal that the crystal structure within BFO thin f...
Article
Full-text available
GaFeO3-type iron oxide is a promising room-temperature multiferroic material due to its large magnetization. To expand its usability, controlling the ferroelectric and magnetic properties is crucial. In this study, high-quality GaxFe2–xO3 (x = 0–1) epitaxial films are fabricated and their properties are systematically investigated. All films exhibi...
Article
Full-text available
Ferroelastic domain switching significantly affects piezoelectric properties in ferroelectric materials. The ferroelastic domain switching and the lattice deformation of both a-domains and c-domains under an applied electric field were investigated using in-situ synchrotron X-ray diffraction in conjunction with a high-speed pulse generator set up f...
Article
ε-Fe2O3-type iron oxide is a promising room-temperature multiferroic material. However, it is difficult to achieve the coexistence of a large magnetization and a reversible polarization due to the large leakage current. In this study, we fabricated highly crystalline codoped ε-Fe2O3 films of A0.2Ga0.4Fe1.4O3 (A = Al, Ga, Sc, and In) and systematica...
Article
Epitaxial thin-film growth techniques are useful for stabilizing metastable phases and controlling crystal-orientations. Herein, we report the fabrication of LuFeO3 films using pulsed laser deposition. A garnet-type structure of the film was obtained because of epitaxial stabilization. The garnet-type LuFeO3 film exhibits ferrimagnetism with a Curi...
Article
We prepared κ-Al2O3-type structured AlxFe2-xO3 films in the range of x = 0 – 1.70 deposited on SrTiO3(111) substrates and investigated their crystal structures and magnetic properties. All films could be stabilized in the κ-Al2O3-type orthorhombic phase, and the lattice parameters were found to be monotonically decreased with an increase in the Al...
Article
Full-text available
Transmission Electron Microscopy and First-Principles Study on Highly Strained BiFeO3 Grown on LaAlO3 - Volume 23 Issue S1 - I.-T. Bae, A. Kovacs, H. J. Zhao, J. Iniguez, S. Yasui, T. Ichinose, H. Naganuma
Article
Recent demonstration of a mechanical 180° switching of ferroelectricpolarization has enabled an alternative polarization control mechanism based on the flexoelectric coupling between polarization and strain gradient. Mechanical switching is a highly asymmetric phenomenon associated with the inhomogeneous strain induced by an atomic force microscope...
Article
In multiferroic GaFeO3 (GFO)-type iron oxides, spontaneous polarization and magnetization coexist at room temperature along the [001]GFO and [100]GFO directions, respectively. Due to the large magnetocrystalline anisotropy and polarization direction in GFO, controlling the domain configuration and orientation is crucial when designing the ferroelec...
Article
Full-text available
A Ga 0.8 Fe 1.2 O 3 epitaxial thin film was fabricated on a SrTiO 3 (111) substrate using pulsed laser deposition. The film is c -axis-oriented and has multiple in-plane domains. In-plane magnetization measurements show that it exhibits ferrimagnetic behavior with a Curie temperature ( TC ) of 290 K. The insulating film exhibits hopping conduction...