Nobumitsu Koyano

A Neutron Diffraction Study of the Ferroelectric Transition of CsH2PO4

Hydrogen atoms in ferroelectric phase of CsH 2 PO 4 have been located from low temperature neutron diffraction experiment. Chains of hydrogen bonds extending to both the crystallographic b - and c -axes are confirmed. The hydrogen atom in a shorter O–H··O bond becomes ordered at low temperature phase with bond length O-H=1.02 A auad H··O=1.46 A. Structural change below T c shows that the hydrogen ordering accompanies a slight rotation of PO 4 tetrahedron about the one P–O bond.

Neutron Diffraction Study of Crystal Structures of Deuterated Glycinium Phosphite in Paraelectric and Ferroelectric Phases

Crystal structure of deuterated glycinium phosphite was studied in the paraelectric (P) phase at 348 K and in the ferroelectric (F) phase at 223 K by means of the single crystal neutron diffraction...

X-Ray diffraction and NMR studies on the crystal structures of MABB and MABA at room temperature

Abstract We have investigated the structures of (CH3NH3)3Bi2Br9 (MABB) and (CH3 NH3)3Sb2Br9 (MABA) crystals by X-ray Fourier method and high resolution 15N-NMR in their prototypic phases. A doublet with intensity ratio 2:1 was observed in the NMR spectrum of MABB. The methyl ammonium cations also showed different electron density distributions at two non-equivalent sites. The distribution was examined in connection with splitting of the Br atoms and the NMR results.

Neutron structural investigation of the isotope effect of KHCO3

Abstract The crystal structures of KHCO3 and KDCO3 have been analyzed from the three-dimensional neutron-diffraction data measured in the high-temperature phase. In the space group C2/m (Z = 4), both the structures are refined successfully with a disordered model. The final R-factors are 0.055 for KHCO3, and 0.047 for KDCO3, respectively. Fourier analysis also reveals that the proton of KHCO3 and deuteron of KDCO3 have two-equilibrium positions separated by 0.616(4) and 0.647(3) A, respectively.

Structure of M(HCOO)2·2(NH2)2CO: M = Mg, Co, Zn

The present status of the structure determination is summarized for the monoclinic C2/c phase of divalent metal formate di-urea. The final result on Mg and Zn salts shows that they consist of a metal-HCOO quasi-quadratic lattice separated by urea molecules.

Structure and Dynamics of Chlorocyclohexane/Thiourea Inclusion Compound C6H11Cl/SC(NH2)2 Studied by X-ray Diffraction and 1H-NMR

Structure and dynamics of chlorocyclohexane/thiourea inclusion compound C 6 H 11 Cl/SC(NH 2 ) 2 have been studied by single crystal X-ray structure analysis and 1 H-NMR. The structure analysis at room temperature disclosed hydrogen bonds in host subunit and molecular arrangement of chlorocyclohexane guest molecule. In the host subunit, thiourea molecule has fairly good planarity and its N and S atoms are bounded by two and four hydrogen bonds grouped into two types, respectively. Inside the thiourea channel, the guest molecules are disordered among six orientations around the special positions with site symmetry D 3d . Proton second moments of C 6 H 11 Cl/SC(NH 2 ) 2 and C 6 H 11 Cl/SC(ND 2 ) 2 gave the following results about the dynamics of the host subunit in the high-temperature phase stable above 197 K. In C 6 H 11 Cl/SC(NH 2 ) 2 , amino group undergoes a uniaxial rotation about its C–N bond, and this rotation begins to freeze at 240 K. For C 6 H 11 Cl/SC(ND 2 ) 2 , the freezing temperature of this r...

NEUTRON STRUCTURAL INVESTIGATION OF LOW AND HIGH TEMPERATURE PHASES OF KDCO3

Abstract Crystal structure of KDCO3 has been analyzed using neutron diffraction data measured just below and above the transition point. Final R-factors are 0.059 in the low-temperature phase and 0.044 in the high-temperature phase. Present structure analysis clearly shows the order-disorder process of the (DCO3)2-dimers.

Structural Investigations of High-Tc Superconducting Untwinned DyBa2Cu3O7-y Single Crystal by X-Ray Diffraction

The crystal structure of high-Tc superconducting orthorhombic DyBa2Cu3O7-y has been determined by X-ray diffraction using an untwinned single crystal. Fourier and difference Fourier analyses revealed exact occupancy factors of O(1) and O(2) in this crystal to be 0.84 and 0.08, respectively. The crystal has one of the highest orthorhombicity ever found with (a-b)/a=0.016, and hence, distinct structural differences of the a and b directions.

Neutron diffraction study on the crystal structures of deuterated and non-deuterated LiTlC4H4O6·H2O (LTT)

Abstract Crystal structure of deuterated LiTlC4H4O6 · H2O was analyzed in the paraelectric phase by using neutron diffraction method and the result was compared with that of non-deuterated LTT reported by Kay. It was clarified that no remarkable difference exists between D- and H-salts but both the salts show characteristic elongation of thermal ellipsoid in one of the hydroxyl hydrogen atom in the tartrate molecule. Preliminary neutron diffraction study proved that space group of D-LTT is P21 in the ferroelectric phase. The symmetry change is similar to that observed in Rochelle salt, but monoclinic spontaneous strain was not detected at 6 K within the experimental error.

Molecular Dynamics Simulation and X-ray Structural Studies of Mode-Coupling in Monoclinic K2ZnBr4

The mode-coupling between the rotational and translational motions in the monoclinic K 2 ZnBr 4 was studied by the molecular dynamics simulation and X-ray structure analysis. In the structure analy...