Nobuo Ishizawa

Electron density and optical anisotropy in rhombohedral carbonates. III: Synchrotron X-ray studies of CaCO3, MgCO3 and MnCO3

Diffraction-deformation electron-density (Δp) images for small, naturally faced single crystals of synthetic calcite (CaCO 3 ), magnesite (MgCO 3 ) and mineral rhodochrosite (MnCO 3 ) were measured with focused λ = 0.7 and 0.9 A synchrotron (SR) X-radiation. Mo Kα (λ = 0.71073 A) structure factors were also measured for MnCO 3 . Lattice mode frequencies predicted from eigenvalues of T and L tensors for CO 3 rigid-group motion in these structures are close to spectroscopic values. High approximate Δp symmetry around the cations increases towards 6/mmm in the sequence CaCO 3 , MgCO 3 to MnCO 3 . The Δp topography near the CO 3 groups shows the influence of the cations, and correlates strongly with the refractive indices, as required for a cause and effect relationship between electron density and optical anisotropy. Aspherical electron density around the Mn atom can be attributed to the effect of a non-ideal octahedral crystal field on the 3d electron distribution. The relationship of the Δp topography near the Mn atom with that near the CO 3 group in MnCO 3 is consistent with magnetic interactions. Space group R3c, hexagonal, Z = 6, T= 295K : CaCO 3 , M r = 100.09, a = 4.988(2), c = 17.068(2) A, V = 367.8(3) A 3 , D x = 2.711 Mg m -3 , μ 0.7 = 1.93 mm -1 , F(000) = 300, R = 0.015, wR = 0.012, S = 3.0 for 437 unique reflections ; MgCO 3 , M r = 84.31, a = 4.632(1), c = 15.007 (2) A, V = 278.8 (2) A 3 , D x = 3.013 Mg m -3 , μ 0.9 = 0.99 mm -1 , F(000) = 252, R = 0.015, wR = 0.021, S = 4.34 for 270 unique reflections ; MnCO 3 , M r = 114.95, a = 4.772(3), c = 15.637 (3) A, V = 308.4 (4) A 3 , D x = 3.713 Mg m -3 , p 0.7 = 5.62 m -1 , F(000) = 330, R = 0.015, wR = 0.039, S = 3.38 for 386 unique reflections of the SR data set and a = 4.773 (1), c = 15.642(1) A, V = 308.6 (1) A 3 , D x = 3.711 Mg m -3 , μ(Mo Kα) = 5.86 mm -1 , R = 0.017, wR = 0.024, S = 2.79 for 368 unique Mo Kα reflections.

Synthesis, crystal structure and spectroscopic study of Para substituted 2-hydroxy-3-methoxybenzalideneanilines

Abstract Eight Schiff bases derived from 2-hydroxy-3-methoxybenzaldehyde and different para substituted anilines have been synthesized and their structures were elucidated by physical measurements and FT-IR. NMR assignments were made using 1H, 13C NMR and aided by 2D COSY homonuclear, HMQC and HMBC heteronuclear correlation techniques. IR spectral analysis of the model compounds was found useful in understanding the degree of stabilization upon this series of enol-imino tautomers, which possess different substituents in the aniline fragment. In order to rationalize the stabilization of tautomer in solid state, the crystallography data of 1-{(4-methylphenylimino)methyl}- and 1-{(4-chlorophenylimino)methyl}-2-hydroxy-3-methoxyphenol were adopted wherein the 4-chloro (4-Cl) and 4-methyl (4-CH3) containing compounds crystallized into orthorhombic lattice with a non-centrosymmetric space group P212121. The relationship between the stabilization of bonding involved in heteronuclear six-membered ring of the tautomer and the conformation of the molecules in crystal phase was reported.

A new delafossite-type compound CuYO2: I. Synthesis and characterization

Abstract Single crystals of a new delafossite-type compound CuYO2 were grown from a Cu2OY2O3 melt by slow cooling from 1210°C. The crystal is hexagonal, P6 3 mmc , a = 3.5206(1) A, c = 11.418(1) A, Z = 2 and Dx = 5.01 g/cm3. Although the crystal belongs to the 2H-polytype of the delafossite family, selected peaks showed a large line broadening on the X-ray powder profile. Correspondingly, diffuse scattering along the c axis was observed for the reflections h − k ≠ 3n on the precession photographs. The approximate crystal structure was analyzed by means of single-crystal X-ray diffraction with a conventional R value of 0.106.

Synchrotron X-ray study of the electron density in α-Al2O3

Structure factors for synthetic haematite, α-Fe 2 O 3 , have been measured for two small crystals using focused λ=0.7 A synchrotron radiation. The structure factors from the two data sets are consistent. Approximate symmetry in the concordant densities, related more closely to the Fe-Fe geometry than to the nearest-neighbour Fe-O interactions, is similar to that in the corundum α-Al 2 O 3 structure. Deformation density maxima are located at the midpoint of the Fe-Fe vector along the c axis, on a common face for O-octahedra, perpendicular to c. Maxima also occur at the midpoint of the Fe-Fe vector bisecting the edges of the O-octahedra. These results are in accordance with theoretical predictions for metal-metal bonding

Thermal stability of Pb(Zn13Nb23)O3 (PZN) and consideration of stabilization conditions of perovskite type compounds

Abstract Thermal stability of Pb(Zn 1 3 Nb 2 3 )O3 (PZN) single crystal was examined in the saturated PbO vapor at 1150 °C for 2h and found that PZN single crystal decomposes into pyrochlore type compound, PbO and ZnO, which indicating that PZN is unstable at high temperature. The reason why PZN single crystal can be grown in the PbO flux at temperature higher than the decomposition into pyrochlore was explained by applying the Ostwalds step rule. The reason PZN can be stabilized by partial substitution of A or B site cations was considered on the basis of the decrease of steric hindrance of lone pair of Pb2+ in the perovskite lattice and decrease of mutual interactions between lone pair and Zn2+. The result of electrostatic potential calculation for each cation and anion in Pb(B′B″)O3 showed that the site potential ratio, f(B′) f(B″) (the valence of B′ is lower than that of B″) is much smaller in A 2+ (B 2+ 1 3 B 5+ 2 3 )O 3 and A 2+ (B 2+ 1 2 B 6+ 1 2 )O 3 than in A 2+ (B 3+ 1 2 B 5+ 1 2 )O 3 and A 2+ (B 3+ 1 3 B 6+ 2 3 )O 3 perovskite type compounds. The result suggested that in A 2+ (B 2+ 1 3 B 5+ 2 3 )O 3 and A 2+ (B 2+ 1 2 B 6+ 1 2 )O 3 type perovskite type compounds, large electronegativity difference from oxygen is required for B′ cation to decrease interaction with lone pair of Pb2+ in addition to the geometrical limit of the ion radius prescribed by the tolerance factor.

High temperature structural investigation of the delafossite type compound CuAlO2

Abstract Crystal structure parameters were determined for the delafossite type compound CuAlO2 at 295, 450, 600, 750, 900, and 1200 K with single crystal high temperature X-ray diffraction technique. Anisotropic refinements result in conventional R values of 0.021, 0.027, 0.029, 0.030, 0.032, and 0.036 at respective temperatures. Crystals of CuAlO2 have the rhombohedral space group R 3 m with a = 2.8584(7), c = 16.958(3) A and Z = 3 at 295 K. The mean thermal expansion coefficient for the dimension a is 11.0 × 10−6 K−1 about three times larger than 4.1 × 10−6 K−1 for c. In the structure, the AlO6 octahedra are linked by their OO edges and form AlO2 layers perpendicular to the c axis with the thickness corresponding to the height of an octahedron. With increasing temperature, the AlO6 octahedra expand along the directions of the basal plane, while expansion scarcely occurs along the c axis. The Cu atom lying between the AlO2 layers shows a large anisotropic behavior in the thermal vibration. The temperature factor for Cu atom in the basal plane becomes very large (0.044 A2) at 1200 K, but the ratio of the temperature factor perpendicular to c to that parallel to c does not change appreciably with increasing temperature.

A fast detector using stacked avalanche photodiodes for x-ray diffraction experiments with synchrotron radiation

We have developed a fast detector using stacked avalanche photodiodes (APDs) for x-ray diffraction experiments with synchrotron radiation. This detector has four independent channels of APDs, and the detector efficiency has reached 55% in all for 16.53 keV x rays. Since the dead time of the counting system is shorter than 4 ns, output rates of up to 4.5×108 counts/s have been obtained for 16.53 keV x rays. The dynamic range is more than 1010 in the multibunch mode of a storage ring. Pulse-height measurements at output rates of up to 108 counts/s were successfully carried out by sequential single-channel discrimination.

A synchrotron X-ray study of the electron density in C-type rare earth oxides

Structure factors for small synthetic crystals of the C-type rare earth (RE) sesquioxides Y2O3, Dy2O3 and Ho2O3 were measured with focused λ = 0.7000 (2) A, synchrotron X-radiation, and for Ho2O3 were re-measured with an MoKα (λ = 0.71073 A) source. Approximate symmetry in the deformation electron density (Δρ) around a RE atom with pseudo-octahedral O coordination matches the cation geometry. Interactions between heavy metal atoms have a pronounced effect on the Δρ map. The electron-density symmetry around a second RE atom is also perturbed significantly by cation–anion interactions. The compounds magnetic properties reflect this complexity. Space group Ia{\bar 3}, cubic, Z = 16, T = 293 K: Y2O3, Mr = 225.82, a = 10.5981 (7) A, V = 1190.4 (2) A3, Dx = 5.040 Mg m−3, μ0.7 = 37.01 mm−1, F(000) = 1632, R = 0.067, wR = 0.067, S = 9.0 (2) for 1098 unique reflections; Dy2O3, Mr = 373.00, a = 10.6706 (7) A, V = 1215.0 (2) A3, Dx = 8.156 Mg m−3, μ0.7 = 44.84 mm−1, F(000) = 2496, R = 0.056, wR = 0.051, S = 7.5 (2) for 1113 unique reflections; Ho2O3, Mr = 377.86, a = 10.606 (2) A, V = 1193.0 (7) A3, Dx = 8.415 Mg m−3, μ0.7 = 48.51 mm−1 F(000) = 2528, R = 0.072, wR = 0.045, S = 9.2 (2) for 1098 unique reflections of the synchrotron data set.

A synchrotron X-ray study of the electron density in YFeO3

Structure factors for synthetic yttrium orthoferrite, YFeO 3 , measured with MoKα (λ = 0.71073 A) X-radiation and using a smaller crystal with focused λ = 0.75 A synchrotron radiation are broadly consistent. Approximate symmetry in concordant difference densities indicates that cations deform the electron density more strongly than O atoms, although the deformation-density (Δp) map symmetry is lower than that expected from Fe cation interactions alone. The maps local symmetry is influenced strongly by the Y cations, but not by neighbouring O anions. Space group Pnma, orthorhombic, M r = 192.76, a = 5.5877 (3), b = 7.5951(4), c = 5.2743 (2) A, V = 223.84 (2) A 3 , Z = 4, D x = 5.719 Mg m -3 , μ 0.75 = 29.82 mm -1 , F(000) = 356, T = 293 K, R = 0.026, wR = 0.028, S = 5.4 (1) for the 1039 unique reflections of the synchrotron data set.

The crystal structure of α-SrMnO3

α-SrMnO3 crystallizes in the hexagonal system with unit-cell dimensions a = 5.454(1) A, c = 9.092(2)A, space group P63mmc, Z = 4. The structure was solved by the heavy-atom method; of 404 unique reflections measured by counter method, 203 that obeyed the condition |F0| ≥ 3σ (|F0|) were used in the refinement to a conventional R value of 0.043. The structure consists of four close-packed SrO3 layers in an ABAC stacking sequence along the hexagonal c axis. Oxygen octahedra containing Mn4+ are grouped into face-sharing pairs linked by corner sharing within the cubically stacked “A” layer.