We studied the orbital ordering of spinel vanadate, MnV2O4. It was found that this compound exhibits a structural phase transition from cubic to tetragonal and ferrimagnetic ordering simultaneously at 57 K, and the structural transition temperature can be varied by applied magnetic field, giving rise to a magnetic-field-induced structural phase transition. We obtained the evidence of antiferro-orbital ordering in the tetragonal phase by X-ray diffraction measurement on the single crystal. This simultaneous spin and orbital ordering can be explained by the coupling between spin and orbital degrees of freedom, called Kugel-Khomkii interaction.
Locations of water molecules and exchangeable cations in a hydrated natural chabazite with a composition of Ca1.57Na0.49 [Al3.39Si8.55O24] ⋅12.47H [d2] O were successfully determined by single crystal X-ray diffraction. The structure analyses have revealed the presences of five partially occupied water sites (OW1-OW5) and four partially occupied exchangeable-cation sites (Ca1-Ca4), and have showed that fully coordinated exchangeable cations can adopt sixfold or sevenfold coordination. The distances between water sites and framework oxygen sites and between water sites suggest that the hydrogen bonds formed between water molecules and framework oxygen atoms are very weak, whereas strong hydrogen bonds exist between water molecules.
1, 2-α-L-Fucosidase (AfcA) is an exoglycosidase recently identified from Bifidobacterium bifidum. To elucidate the molecular mechanism of this enzyme, we determined the X-ray crystal structures of the AfcA catalytic domain in unliganded and complexed forms with inhibitor, substrate and products at atomic resolution. A series of the structural and the biochemical analyses provides insight into a novel catalytic mechanism for this enzyme.
The phase transition behavior of perovskite-type compounds, La1-xSrxCrO3, was investigated by differential scanning calorimetry, measurement of do magnetic property and X-ray diffraction at regulated temperatures. The phase diagram of La1-xSrxCrO3 has been established, which includes four phases, paramagnetic orthorhombic, canted antiferromagnetic orthorhombic, canted antiferromagnetic rhombohedral and paramagnetic rhombohedral. It was also revealed that magnetic properties such as residual magnetization (Mr) and coercive force (Hc) were affected by the variation of crystal structure from orthorhombic to rhombohedral. It was suggested that decrease of deviation of Cr-O-Cr angle from 180° by the structural phase transition decreased Mr and Hc observed in La1-xSrxCrO3 with x larger than 0.11.
Recent works revealed that a ferroelectric polarization in the charge-frustrated system LuFe2O4 originates from an emergence of the charge ordering, which is characterized by a regular arrangement of Fe2+ and Fe3+ ions on the frustrated triangular lattice. In this work, we have investi-gated both the charge ordered (CO) structure and charge ordering processes mainly by means of the transmission electron microscopy (TEM) . Both the CO structure and charge ordering processes depend strongly on the amount of the oxygen deficiency (δ) involved in LuFe2O4-δ. In the case of δ-0, the three-dimensional CO structure with the modulation vector of q= [1/3 1/3 1/2] was formed at room temperature. On the other hand, as δ was increased, the three-dimensional CO structure changed into the two-dimensional CO one and the coherent length becomes shorter along the  direction. For proper understanding of the dielectric and magnetic properties in LuFe2O4 and related materials, it should be essential to prepare LuFe2O4-δ samples with properly controlled oxygen-concentration and elucidate the physical properties in LuFe2O4-δ with δ-0.
Perovskite-type proton conductors can be used as the electrolyte materials in fuel cells, hydrogen sensors, hydrogen separation apparatus, and the other electrochemical devices. In this paper, the crystal structure analysis of perovskite-type proton conductors under cell operating conditions by using a laboratory X-ray diffractometer with a parallel beam optics are introduced. The crystal structures of A3+B3+O3-type perovskite proton conductors, (La0.9Sr0.1) MIIIO3-δ (MIII=Sc, In, and Lu) are reported, and the expected change in proton conduction path is discussed with an increase in tilting angles of BO6 (=MIIIO6) octahedra. In addition, the electron density distribution of (La0.8Sr0.2) ScO3-δ compound is shown.
Pombe Cdc 15 homology (PCH) proteins are involved in a variety of actin-based processes, including clathrin-mediated endocytosis. The PCH proteins contain an evolutionarily conserved, EFC/F-BAR domain for membrane association and tubulation. We solved the crystal structures of the EFC domains of human FBP 17 and CIP4. The structures revealed a gently-curved helicalbundle dimer, which forms filaments through end-to-end interactions in the crystals. The structural and biochemical data suggested a mechanistic model, in which the curved EFC filament drives tubulation. The electron micrographs of the EFC-induced tubular membranes supported this model. The physiological role of the EFC domain in clathrin-mediated endocytosis is discussed.
Ferroelectric materials with layered structure have attracted a great deal of attention in technological and scientific points of view because of their high Curie temperature and large spontaneous polarization. The current status and problems of representative layered ferroelectric material, Bi4Ti3O12, are briefly reviewed. Piezoresponse force microscopy observations reveal that the clamping of 90° domain walls is the origin of poor polarization properties of Bi4Ti3O12 crystals. The origin of the domain clamping is suggested to be the strong interaction between oxygen vacancies and 90° domain walls. High-pressure-oxygen sintering is shown to be effective processing for obtaining high-quality Bi4Ti3O12-based devices with superior polarization properties.