Yuichi Ikuhara

Bio: Yuichi Ikuhara is an academic researcher from University of Tokyo. The author has contributed to research in topics: Grain boundary & Scanning transmission electron microscopy. The author has an hindex of 75, co-authored 974 publications receiving 24224 citations. Previous affiliations of Yuichi Ikuhara include Kyushu University & Tokyo Institute of Technology.

Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3

Abstract: Enhancement of the Seebeck coefficient (S ) without reducing the electrical conductivity (sigma) is essential to realize practical thermoelectric materials exhibiting a dimensionless figure of merit (ZT=S2 x sigma x T x kappa-1) exceeding 2, where T is the absolute temperature and kappa is the thermal conductivity. Here, we demonstrate that a high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO(3) yields unusually large |S|, approximately five times larger than that of SrTiO(3) bulks, while maintaining a high sigma2DEG. In the best case, we observe |S|=850 microV K-1 and sigma2DEG=1.4 x 10(3) S cm-1. In addition, by using the kappa of bulk single-crystal SrTiO(3) at room temperature, we estimate ZT approximately 2.4 for the 2DEG, corresponding to ZT approximately 0.24 for a complete device having the 2DEG as the active region. The present approach using a 2DEG provides a new route to realize practical thermoelectric materials without the use of toxic heavy elements.

Direct atomic-scale confirmation of three-phase storage mechanism in Li 4 Ti 5 O 12 anodes for room-temperature sodium-ion batteries

Abstract: The development of suitable anode materials for room-temperature sodium-ion batteries remains a challenging issue. Sun et al. show that the well-known zero-strain Li4Ti5O12 anode for lithium storage is capable of reversibly hosting sodium ions via a three-phase storage mechanism.

Rutile-TiO2 nanocoating for a high-rate Li4Ti5O12 anode of a lithium-ion battery.

Abstract: Well-defined Li4Ti5O12 nanosheets terminated with rutile-TiO2 at the edges were synthesized by a facile solution-based method and revealed directly at atomic resolution by an advanced spherical aberration imaging technique. The rutile-TiO2 terminated Li4Ti5O12 nanosheets show much improved rate capability and specific capacity compared with pure Li4Ti5O12 nanosheets when used as anode materials for lithium ion batteries. The results here give clear evidence of the utility of rutile-TiO2 as a carbon-free coating layer to improve the kinetics of Li4Ti5O12 toward fast lithium insertion/extraction. The carbon-free nanocoating of rutile-TiO2 is highly effective in improving the electrochemical properties of Li4Ti5O12, promising advanced batteries with high volumetric energy density, high surface stability, and long cycle life compared with the commonly used carbon nanocoating in electrode materials.

Electrically induced ferromagnetism at room temperature in cobalt-doped titanium dioxide.

Abstract: The electric field effect in ferromagnetic semiconductors enables switching of the magnetization, which is a key technology for spintronic applications. We demonstrated electric field–induced ferromagnetism at room temperature in a magnetic oxide semiconductor, (Ti,Co)O2, by means of electric double-layer gating with high-density electron accumulation (>1014 per square centimeter). By applying a gate voltage of a few volts, a low-carrier paramagnetic state was transformed into a high-carrier ferromagnetic state, thereby revealing the considerable role of electron carriers in high-temperature ferromagnetism and demonstrating a route to room-temperature semiconductor spintronics.

Grain Boundary Strengthening in Alumina by Rare Earth Impurities

Abstract: Impurity doping often alters or improves the properties of materials. In alumina, grain boundaries play a key role in deformation mechanisms, particularly in the phenomenon of grain boundary sliding during creep at high temperatures. We elucidated the atomic-scale structure in alumina grain boundaries and its relationship to the suppression of creep upon doping with yttrium by using atomic resolution microscopy and high-precision calculations. We find that the yttrium segregates to very localized regions along the grain boundary and alters the local bonding environment, thereby strengthening the boundary against mechanical creep.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Mechanical Alloying And Milling

Abstract: Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Sodium-ion batteries: present and future

Abstract: Energy production and storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, recent research has focused on alternative energy storage systems. Sodium-ion batteries (SIBs) are considered as the best candidate power sources because sodium is widely available and exhibits similar chemistry to that of LIBs; therefore, SIBs are promising next-generation alternatives. Recently, sodiated layer transition metal oxides, phosphates and organic compounds have been introduced as cathode materials for SIBs. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal oxides (or sulfides), and intermetallic and organic compounds as anodes for SIBs. Apart from electrode materials, suitable electrolytes, additives, and binders are equally important for the development of practical SIBs. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium ion cells. In this article, we summarize and discuss current research on materials and propose future directions for SIBs. This will provide important insights into scientific and practical issues in the development of SIBs.