Susumu Tsukimoto

Reversible Storage of Lithium in Silver‐Coated Three‐Dimensional Macroporous Silicon

[*] Dr. Y. Yu, C. Zhu, Prof. Dr. J. Maier Max Planck Institute for Solid State Research Heisenbergstrasse 1, 70569 Stuttgart (Germany) E-mail: yan.yu@fkf.mpg.de Dr. L. Gu, Prof. S. Tsukimoto WPI Advanced Institute for Materials Research Tohoku University 2-1-1 Katahira Aoba-ku, Sendai 980-8577 (Japan) E-mail: gu@wpi-aimr.tohoku.ac.jp Dr. L. Gu, Dr. P. A. van Aken Stuttgart Center for Electron Microscopy Max Planck Institute for Metals Research Heisenbergstrasse 3, 70569 Stuttgart (Germany)

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

The magnetic properties of a magnetic insulator can be controlled by an electric field at room temperature. 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.

Low-temperature ionic-liquid-based synthesis of nanostructured iron-based fluoride cathodes for lithium batteries

Recently, the fabrication of nanostructured cathode materials for rechargeable lithium-ion batteries is being paid considerable attention to in order to enlarge the contact area with the electrolyte, to increase the surface reactivity and to shorten both electronic and ionic pathways within particles. [ 1 , 2 ] For nanometersized LiFePO 4 in particular, high specifi c capacity, excellent rate capability and long cycling life have been achieved, even though the detailed reaction mechanisms remain controversial. [ 3 , 4 ]

Direct Observation of Lithium Staging in Partially Delithiated LiFePO4 at Atomic Resolution

Lithium ions in LiFePO(4) were observed directly at atomic resolution by an aberration-corrected annular-bright-field scanning transmission electron microscopy technique. In addition, it was found in partially delithiated LiFePO(4) that the remaining lithium ions preferably occupy every second layer, along the b axis, analogously to the staging phenomenon observed in some layered intercalation compounds. This new finding challenges previously proposed LiFePO(4)/FePO(4) two-phase separation mechanisms.

Atom-resolved imaging of ordered defect superstructures at individual grain boundaries

The ability to resolve spatially and identify chemically atoms in defects would greatly advance our understanding of the correlation between structure and property in materials. This is particularly important in polycrystalline materials, in which the grain boundaries have profound implications for the properties and applications of the final material. However, such atomic resolution is still extremely difficult to achieve, partly because grain boundaries are effective sinks for atomic defects and impurities, which may drive structural transformation of grain boundaries and consequently modify material properties. Regardless of the origin of these sinks, the interplay between defects and grain boundaries complicates our efforts to pinpoint the exact sites and chemistries of the entities present in the defective regions, thereby limiting our understanding of how specific defects mediate property changes. Here we show that the combination of advanced electron microscopy, spectroscopy and first-principles calculations can provide three-dimensional images of complex, multicomponent grain boundaries with both atomic resolution and chemical sensitivity. The high resolution of these techniques allows us to demonstrate that even for magnesium oxide, which has a simple rock-salt structure, grain boundaries can accommodate complex ordered defect superstructures that induce significant electron trapping in the bandgap of the oxide. These results offer insights into interactions between defects and grain boundaries in ceramics and demonstrate that atomic-scale analysis of complex multicomponent structures in materials is now becoming possible.

Dimensionality-driven insulator–metal transition in A-site excess non-stoichiometric perovskites

Coaxing correlated materials to the proximity of the insulator–metal transition region, where electronic wavefunctions transform from localized to itinerant, is currently the subject of intensive research because of the hopes it raises for technological applications and also for its fundamental scientific significance. In general, this tuning is achieved by either chemical doping to introduce charge carriers, or external stimuli to lower the ratio of Coulomb repulsion to bandwidth. In this study, we combine experiment and theory to show that the transition from well-localized insulating states to metallicity in a Ruddlesden-Popper series, La0.5Srn+1−0.5TinO3n+1, is driven by intercalating an intrinsically insulating SrTiO3 unit, in structural terms, by dimensionality n. This unconventional strategy, which can be understood upon a complex interplay between electron–phonon coupling and electron correlations, opens up a new avenue to obtain metallicity or even superconductivity in oxide superlattices that are normally expected to be insulators.

Highly ordered staging structural interface between LiFePO4 and FePO4

A highly ordered interface between LiFePO(4) phase and FePO(4) phase with staging structure along the a axis and perpendicular to the b axis direction has been observed for the first time, in a partially chemically delithiated Li(0.90)Nb(0.02)FePO(4) by advanced aberration-corrected annular-bright-field (ABF) scanning transmission electron microscopy (STEM).

Atomic-scale structure and electronic property of the LaAlO3/TiO2 interface

Combining advanced transmission electron microscopy with high-precision first-principles calculation, atomic-scale structures of the LaAlO3/TiO2 interface are investigated and bridged to their electronic property at the atomic level. Experimentally, the deposited TiO2 thin film is demonstrated to have an anatase phase and bond directly to the LaAlO3 substrate in an epitaxial, coherent, and atomically abrupt fashion. The atomic-resolution microscopic images reveal that the interface can be terminated with either AlO2 or LaO layer, which is predicted in theory to exhibit a semiconducting or metallic nature at interface, respectively. By applying several analytic methods, we characterize carefully the electronic structure and determine interfacial bonding to be of a mixed covalent-ionic character. The combined experimental and theoretical studies performed shed light on the complex atomic and electronic structures of the buried interface, which are fundamental for understanding the promising properties of fu...

Origins of structural and electrochemical influence on Y-doped BaZrO3 heat-treated with NiO additive

Nickel (Ni) is expected to be an attractive anode material for protonic ceramic fuel cells using Y-doped BaZrO3 (BZY) as an electrolyte, since Ni shows good catalytic properties for the anode reaction, and NiO is a sintering aid for BZY. In this work, a systematic investigation has been performed to reveal the influence of Ni incorporation on structural and electrochemical properties of BZY. Then, some new knowledge was obtained; the important point is that Ni cations occupy the interstitial position of (1/2, 0, 0) in the lattice of BZY, with a greatly Ba-deficient environment. As a result, Ba cations were possibly driven to the grain boundary and induced the formation of a liquid phase, which promoted the sintering process. However, the occupation of Ni on this (1/2, 0, 0) position also resulted in a negative influence on conductivity. A careful processing is required to apply Ni as the electrode in BZY based fuel cells.

Interface Atomic‐Scale Structure and its Impact on Quantum Electron Transport

Local structure, chemistry, and bonding at interfaces often radically affect the properties of materials. A combination of scanning transmission electron microscopy and density functional theory calculations reveals an atomic layer of carbon at a SiC/Ti3 SiC2 interface in Ohmic contact to p-type SiC, which results in stronger adhesion, a lowered Schottky barrier, and enhanced transport. This is a key factor to understanding the origin of the Ohmic nature.