Cerium Oxide Nanorods with Unprecedented Low-Temperature Oxygen Storage Capacity.

Ultrafine cerium oxide nanorods are produced from rapidly liquid quenched Ce-Al alloy precursors by a corrosion method through the selective leaching of Al and the oxidation of Ce in an alkaline medium under mild conditions. The obtained nanorods, having 5-7 nm diameter, exhibit unprecedented low-temperature oxygen-storage capacity (OSC) performance.

Ultrafine sodium titanate nanowires with extraordinary Sr ion-exchange properties.

Ultrafine sodium titanate nanowires are produced from TiAl alloy precursors via a nonthermal process where Al leaching and Ti oxidation occur simultaneously in an alkaline medium. The obtained nanowires demonstrate a layered crystal structure with a diameter of a few nanometers and exhibit remarkable Sr ion-exchange properties.

Spontaneous structural distortion and quasi-one-dimensional quantum confinement in a single-phase compound.

Oxide heterointerfaces often trigger unusual electronic properties that are absent in respective bulks. Here, direct evidence is offered for spontaneously assembled local structural distortions in a single-phase bulk, which confine electrons to within an atomic layer with notable orbital reconstruction and coupling, close the forbidden band, induce a ferromagnetic ordering, and give rise to a strongly anisotropic, spin-polarized quasi-one-dimensional electron gas.

New insight into the atomic structure of electrochemically delithiated O3-Li(1-x)CoO2 (0 ≤ x ≤ 0.5) nanoparticles.

Direct observation of delithiated structures of LiCoO(2) at atomic scale has been achieved using spherical aberration-corrected scanning transmission electron microscopy (STEM) with high-angle annular-dark-field (HAADF) and annular-bright-field (ABF) techniques. The ordered Li, Co, and O columns for LiCoO(2) nanoparticles are clearly identified in ABF micrographs. Upon the Li ions extraction from LiCoO(2), the Co-contained (003) planes distort from the bulk to the surface region and the c-axis is expanded significantly. Ordering of lithium ions and lithium vacancies has been observed directly and explained by first-principles simulation. On the basis of HAADF micrographs, it is found that the phase irreversibly changes from O3-type in pristine LiCoO(2) to O1-type Li(x)CoO(2) (x ≈ 0.50) after the first electrochemical Li extraction and back to O2-type Li(x)CoO(2) (x ≈ 0.93) rather than to O3-stacking after the first electrochemical lithiation. This is the first report of finding O2-Li(x)CoO(2) in the phase diagram of O3-LiCoO(2), through which the two previously separated LiCoO(2) phases, i.e. O2 and O3 systems, are connected. These new investigations shed new insight into the lithium storage mechanism in this important cathode material for Li-ion batteries.

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

Well-defined Li(4)Ti(5)O(12) nanosheets terminated with rutile-TiO(2) 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-TiO(2) terminated Li(4)Ti(5)O(12) nanosheets show much improved rate capability and specific capacity compared with pure Li(4)Ti(5)O(12) nanosheets when used as anode materials for lithium ion batteries. The results here give clear evidence of the utility of rutile-TiO(2) as a carbon-free coating layer to improve the kinetics of Li(4)Ti(5)O(12) toward fast lithium insertion/extraction. The carbon-free nanocoating of rutile-TiO(2) is highly effective in improving the electrochemical properties of Li(4)Ti(5)O(12), 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.

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).

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.

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.

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, La(0.5)Sr(n+1-0.5)Ti(n)O(3n+1), is driven by intercalating an intrinsically insulating SrTiO(3) 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.

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.

Selective Detection of Formaldehyde Gas Using a Cd-Doped TiO(2)-SnO(2) Sensor.

We report the microstructure and gas-sensing properties of a nonequilibrium TiO(2)-SnO(2) solid solution prepared by the sol-gel method. In particular, we focus on the effect of Cd doping on the sensing behavior of the TiO(2)-SnO(2) sensor. Of all volatile organic compound gases examined, the sensor with Cd doping exhibits exclusive selectivity as well as high sensitivity to formaldehyde, a main harmful indoor gas. The key gas-sensing quantities, maximum sensitivity, optimal working temperature, and response and recovery time, are found to meet the basic industrial needs. This makes the Cd-doped TiO(2)-SnO(2) composite a promising sensor material for detecting the formaldehyde gas.

In situ HREM observation of nucleation and growth of nanotwins beneath the solid-liquid interface in Si.

Nucleation and growth of nanotwins in Si grown from Al-Si liquid have been observed directly using an in situ heating experiment in a high-resolution transmission electron microscope. Nanotwins are nucleated at the triple point between a vacuum and the solid-liquid interface. When two parallel twins, the mirror planes of which are separated slightly, encounter each other, very complicated atomic arrangements are formed. The structure of the perturbed region is discussed tentatively in terms of the high-pressure phases in Si.