Institute of Materials Structure Science

The crystal structures of Bi4Ti3O12 and Bi3.25La0.75Ti3O12 were refined by neutron powder diffraction. Large structural distortions were revealed, and ferroelectric polarizations along the a and c axes were calculated from the displacements of the constituent ions. In Bi3.25La0.75Ti3O12, La atoms substitute for Bi atoms in a perovskite-type unit only, and the substitution causes less distortion of the structure, resulting in smaller spontaneous polarization and lower ferroelectric Curie temperature. Electronic-structure calculations revealed that covalent interaction, which originates from the strong hybridization between Ti 3d and O 2p orbitals, plays an important role in the structural distortion and ferroelectricity of the materials. Changes in ceramic-sample density with sintering temperature give information concerning device fabrication temperature; that is, substituting La for Bi atoms appears to “increase” the synthesis temperature of the Bi4Ti3O12 and Bi3.25La0.75Ti3O12 systems.

A lightly doped manganite ${\mathrm{La}}_{0.88}{\mathrm{Sr}}_{0.12}{\mathrm{MnO}}_{3}$ exhibits a phase transition at ${T}_{\mathrm{OO}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}145\phantom{\rule{0ex}{0ex}}\mathrm{K}$ from a ferromagnetic metal ( ${T}_{C}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}172\phantom{\rule{0ex}{0ex}}\mathrm{K}$) to a novel ferromagnetic insulator. We identify that the key parameter in the transition is the orbital degree of freedom in ${e}_{g}$ electrons. By utilizing the resonant x-ray scattering, orbital ordering is directly detected below ${T}_{\mathrm{OO}}$, in spite of a significant diminution of the cooperative Jahn-Teller distortion. The experimental features are well described by a theory treating the orbital degree of freedom under strong electron correlation. The present studies uncover a crucial role of the orbital degree of freedom in the metal-insulator transition in lightly doped manganites.

The spin dynamics of the underdoped superconductor ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.7}$ ( ${T}_{c}\ensuremath{\sim}67\mathrm{K}$) was revealed to have an incommensurate wave vector dependence with ``pillars'' in the dispersion relation at the positions ( $\frac{1}{2}\ifmmode\pm\else\textpm\fi{}d,\frac{1}{2},0$) and ( $\frac{1}{2},\frac{1}{2}\ifmmode\pm\else\textpm\fi{}d,0$). This is the same symmetry as that found in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$. The value of the incommensurability, $d\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.11\ifmmode\pm\else\textpm\fi{}0.01\mathrm{r}.\mathrm{l}.\mathrm{u}\ensuremath{\sim}\frac{1}{8}$, is very close to the value expected from the hole concentration. These results have demonstrated that the spin dynamics do not depend on the details of Fermi surface but have an analogous form to that for the proposed stripe domain structure.

Structural and electronic properties have been investigated for a series of Re-based ordered double perovskites, ${A}_{2}M{\mathrm{ReO}}_{6}$ $(A$=Sr,Ca; $M$=Mg,Sc,Cr,Mn,Fe,Co,Ni,Zn), which contain some prospective candidates of the high-temperature half-metals for future spin-electronic use. Neutron diffraction measurements have revealed the variation of the Re-O bond length with the change of its effective valence states depending on the counter M ion, namely, ${\mathrm{Re}}^{6+}$- or ${\mathrm{Re}}^{5+}$-based insulating states, or otherwise mixed-valent metallic (or barely Mott-insulating) states. Magnetotransport and specific heat studies have clarified metal-insulator phenomena for $M$=Cr and Fe compounds with the change of A site as well as the intergrain tunneling magnetoresistance characteristic of the ceramics of half-metal oxides.

α-Synuclein plays a central causative role in Parkinson's disease (PD). Increased expression of the P-type ATPase ion pump PARK9/ATP13A2 suppresses α-Synuclein toxicity in primary neurons. Our data indicate that ATP13A2 encodes a zinc pump; neurospheres from a compound heterozygous ATP13A2(-/-) patient and ATP13A2 knockdown cells are sensitive to zinc, whereas ATP13A2 over-expression in primary neurons confers zinc resistance. Reduced ATP13A2 expression significantly decreased vesicular zinc levels, indicating ATP13A2 facilitates transport of zinc into membrane-bound compartments or vesicles. Endogenous ATP13A2 localized to multi-vesicular bodies (MVBs), a late endosomal compartment located at the convergence point of the endosomal and autophagic pathways. Dysfunction in MVBs can cause a range of detrimental effects including lysosomal dysfunction and impaired delivery of endocytosed proteins/autophagy cargo to the lysosome, both of which have been observed in cells with reduced ATP13A2 function. MVBs also serve as the source of intra-luminal nanovesicles released extracellularly as exosomes that can contain a range of cargoes including α-Synuclein. Elevated ATP13A2 expression reduced intracellular α-Synuclein levels and increased α-Synuclein externalization in exosomes >3-fold whereas ATP13A2 knockdown decreased α-Synuclein externalization. An increased export of exosome-associated α-Synuclein may explain why surviving neurons of the substantia nigra pars compacta in sporadic PD patients were observed to over-express ATP13A2. We propose ATP13A2's modulation of zinc levels in MVBs can regulate the biogenesis of exosomes capable of containing α-Synuclein. Our data indicate that ATP13A2 is the first PD-associated gene involved in exosome biogenesis and indicates a potential neuroprotective role of exosomes in PD.

For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm(2)/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.

The lithium diffusion pathway in the LGPS structure visualized through MEM analysis assisted in elucidating the conductivity pathway changes with temperature.

Phase transitions in calcite, a naturally occurring crystalline form of CaCO3, have been investigated by three different experimental techniques: (1) in-situ X-ray diffraction (XRD) using synchrotron radiation to 6 GPa and 1750 °C in a cubic anvil press; (2) Raman scattering to 10 GPa at room temperature using a diamond-anvil cell; and (3) post-compression XRD on samples retrieved after heat treatment at temperatures to 2000 °C and pressures to 9 GPa in an octahedral anvil press. At room temperature, calcite I transformed into calcite II at 1.7 GPa and then to calcite III at ~2 GPa. Calcite III persisted to at least 10 GPa. Elevation of temperature at 3, 4, and 6 GPa caused a sequence of transitions: calcite III → aragonite → disordered calcite → liquid, and aragonite was retained upon rapid cooling of the liquid. The melting curve of disordered calcite increased with pressure following a relation: Tm (°C) = 1338 + 82 P - 2.9 P2 where P is in units of GPa.

We report a ferroelectric transition driven by the off-centering of magnetic Mn(4+) ions in antiferromagnetic Mott insulators Sr(1-x)Ba(x)MnO(3) with a perovskite structure. As x increases, the perovskite lattice shows the typical soft-mode dynamics, as revealed by the momentum-resolved inelastic x-ray scattering and far-infrared spectroscopy, and the ferroelectricity shows up for x ≥ 0.45. The observed polarization is comparable to that for a prototypical ferroelectric BaTiO(3). We further demonstrate that the magnetic order suppresses the ferroelectric lattice dilation by ∼70% and increases the soft-phonon energy by ∼50%, indicating the largest magnetoelectric effects yet attained.

As synchrotron light sources and optics deliver greater photon flux on samples, X-ray-induced photo-chemistry is increasingly encountered in X-ray absorption spectroscopy (XAS) experiments. The resulting problems are particularly pronounced for biological XAS experiments. This is because biological samples are very often quite dilute and therefore require signal averaging to achieve adequate signal-to-noise ratios, with correspondingly greater exposures to the X-ray beam. This paper reviews the origins of photo-reduction and photo-oxidation, the impact that they can have on active site structure, and the methods that can be used to provide relief from X-ray-induced photo-chemical artifacts.

A scanning tunneling microscopy study and ab initio total energy calculations have identified the atomic-level structure of novel sp;{3}-bonded carbon nanoscale domains formed dynamically from graphite by femtosecond-laser excitation. The structure is characterized by a pseudo sp;{3}-bonding configuration that results in inward displacement of surface carbon atoms by 0.5 A in every third row along the [11[over ]00] orientation. This structural periodicity is unique and differs from conventional phases of diamond.

The scattering intensities measured by small-angle X-ray scattering (SAXS) experiment are generally recorded as a two-dimensional image data these days. The intensities are converted into a one-dimensional data by azimuthal average for the structural analysis. We developed the GUI software, SAngler for data analysis with mainly the PILATUS data. SAngler was developed by Microsoft Visual Studio Express 2013 for Windows and the program language of C#, and runs on Windows 7 and 8.1 64bit. It can perform the several basic analysis for SAXS data after the conversion from 2D image and 1D data.

Antiferroquadrupolar (AFQ) ordering has been conjectured in several rare-earth compounds to explain their anomalous magnetic properties. No direct evidence for AFQ ordering, however, has been reported. Using the resonant x-ray scattering technique near the Dy L(III) absorption edge, we have succeeded in observing the AFQ order parameter in DyB2C2 and analyzing the energy and polarization dependence. The much weaker coupling between the orbital degrees of freedom and the lattice in 4f electron systems than in 3d compounds makes them an ideal platform to study orbital interactions originating from electronic mechanisms.

Abstract— We compare the observed composition ranges of olivine, pyroxene, and Fe‐Ni sulfides in Wild 2 grains with those from chondritic interplanetary dust particles (IDPs) and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular. Wild 2 olivine has an extremely wide composition range, from Fa 0–96 , with a pronounced frequency peak at Fa 1 . The composition range displayed by the low‐calcium pyroxene is also very extensive, from Fs 48 to Fs 0 , with a significant frequency peak centered at Fs 5 . These ranges are as broad or broader than those reported for any other extraterrestrial material. Wild 2 Fe‐Ni sulfides mainly have compositions close to that of FeS, with less than 2 atom% Ni; to date, only two pentlandite grains have been found among the Wild grains, suggesting that this mineral is not abundant. The complete lack of compositions between FeS and pentlandite (with intermediate solid solution compositions) suggests (but does not require) that FeS and pentlandite condensed as crystalline species, i.e., did not form as amorphous phases, which later became annealed. While we have not yet observed any direct evidence of water‐bearing minerals, the presence of Ni‐bearing sulfides, and magnesium‐dominated olivine and low‐Ca pyroxene does not rule out their presence at low abundance. We do conclude that new investigations of major‐ and minor‐ element compositions of chondrite matrix and IDPs are required.

In situ thickness-dependent photoemission spectroscopy (PES) has been performed on SrRuO3 (SRO) layers deposited on SrTiO3 substrates to study the structure-induced evolution of the electronic structure. The PES spectra showing the existence of two critical film thicknesses reveal that a metal-insulator transition occurs at a film thickness of 4–5 monolayers (ML) and the evolution of Ru 4d-derived states around the Fermi level (EF) saturates at about 15 ML. The observed spectral behavior well matches the electric and magnetic properties and thickness-dependent evolution of surface morphology of the ultrathin SRO films. These experimental results suggest the importance of the disorder associated with the unique growth-mode transition in SRO films.

We have investigated the doping and temperature dependences of the pseudogap and superconducting gap in the single-layer cuprate ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ by angle-resolved photoemission spectroscopy. The results clearly exhibit two distinct energy and temperature scales, namely, the gap around ($\ensuremath{\pi}$, 0) of magnitude ${\ensuremath{\Delta}}^{*}$ and the gap around the node characterized by the $d$-wave order parameter ${\ensuremath{\Delta}}_{0}$. In comparison with Bi2212 having higher ${T}_{c}$'s, ${\ensuremath{\Delta}}_{0}$ is smaller, while ${\ensuremath{\Delta}}^{*}$ and ${T}^{*}$ are similar. This result suggests that ${\ensuremath{\Delta}}^{*}$ and ${T}^{*}$ are approximately material-independent properties of a single ${\mathrm{CuO}}_{2}$ plane, in contrast to the material-dependent ${\ensuremath{\Delta}}_{0}$, representing the pairing strength.

The disintegration of Rh clusters on an Al2O3 surface induced by CO, the elementary steps, and timescale of the reaction are analyzed for the first time by energy-dispersive X-ray absorption fine structure (DXAFS) at a time resolution of 100 ms (see picture). This study by the improved time-resolved DXAFS technique provides a new research area of structural dynamics of catalytically active materials at surfaces.

We have succeeded in observing nuclear excitation by electron transition (NEET) in ${}^{197}\mathrm{Au}$ by a new method. Monochromatic x-rays of synchrotron radiation were used to ionize the $K$ shell of gold atoms in a target foil. The internal-conversion electrons emitted from excited nuclei were detected with a silicon avalanche photodiode. At a photon energy of 80.989 keV, the NEET probability in ${}^{197}\mathrm{Au}$ was determined to be $(5.0\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ from a comparison of the event number per photon between NEET and the nuclear resonance at 77.351 keV.

Der CO-induzierte Abbau von Rh-Clustern auf einer Al2O3-Oberfläche wurde mithilfe der energiedispersiven Röntgenabsorptionsspektroskopie (DXAFS) mit einer Zeitauflösung von 100 ms in Elementarschritten verfolgt (siehe Bild). Diese verbesserte, zeitaufgelöste DXAFS-Technik ermöglicht die detaillierte Untersuchungen der Strukturdynamik katalytisch aktiver Materialoberflächen.

Multiferroic materials have attracted much interest due to the unusual coexistence of ferroelectric and (anti-)ferromagnetic ground states in a single compound. They offer an exciting platform for new physics and potentially novel devices. BiFeO3 is one of the most celebrated multiferroic materials and has highly desirable properties. It is the only known room-temperature multiferroic with TC ≈ 1100 K and TN ≈ 650 K, and exhibits one of the largest spontaneous electric polarisations, P ≈ 80 µC cm(-2). At the same time, it has a magnetic cycloid structure with an extremely long period of 620 Å, which arises from competition between the usual symmetric exchange interaction and the antisymmetric Dzyaloshinskii-Moriya (DM) interaction. There is also an intriguing interplay between the DM interaction and single ion anisotropy K. In this review, we have attempted to paint a complete picture of bulk BiFeO3 by summarising the structural and dynamic properties of both the spin and lattice parts and their magneto-electric coupling.