Structural phase transition and magnetic-field effect on the modulated structure in GdBaCo2O5+δ (δ < 0.5).

We investigated the crystal structures of an ordered perovskite-type cobaltate, GdBaCo2O(5+δ) (δ < 0.5), at elevated temperatures by transmission electron microscopy. Above the magnetic ordering temperature, we observed a first-order structural phase transition between the low-temperature tetragonal 3a(p) × 3a(p) and high-temperature orthorhombic 1a(p) × 2a(p) superstructure phases (where a(p) is the perovskite-unit cell). Upon the application of a magnetic field, an incommensurate phase emerges around the structural phase-transition temperature, which indicates a magnetic-field-induced structural phase transition via no magnetic ordering in the ordered perovskite-type cobaltate.

Fabrication and optical properties of Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) thin films on Si substrates using the PLD method.

Epitaxial 0.67Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3)-0.33PbTiO(3) (PMN-PT) thin films with electro-optic effects were fabricated on (PMN-PT) thin films with electro-optic effects were fabricated on (La0(0.5)Sr0(0.5))CoO(3) (LSCO)/CeO(2)/YSZ-buffered Si(001) substrates using double-pulse excitation pulsed laser deposition (PLD) method with a mask placed between the target and the substrate. Epitaxial growth of PMN-PT thin films was undertaken using the two-step growth method of PMN-PT film. The PMN-PT seed layer was deposited at 500 degrees C on the LSCO/CeO(2)/YSZ/Si, which temperature was the same as that used for LSCO deposition. The PMN-PT thin films were deposited on the PMN-PT seed layer at 600 degrees C, which enables growth of high-crystallinity PMN-PT films with smooth surfaces. We obtained optimum fabrication conditions of PMNPT film with micrometer-order thickness. Resultant films showed high crystallinity with full width at half maximum (FWHM) = 0.73 deg and 1.6 mum thickness. Electro-optic properties and the refractive index value were measured at 633 nm wavelength using the prism coupling method. The obtained refractive index was 2.59. The electro-optic coefficients r(13) and r(33) were determined by applying the electrical field between a semitransparent, thin top electrode of Pt and a bottom LSCO electrode. The electro-optic coefficient was r(13) = 17 pm/V at transverse electric field (TE) mode and r(33) = 55 pm/V at transverse magnetic field (TM) mode.

Synchrotron X-ray and ab initio studies of beta-Si3N4.

Almost absorption- and extinction-free single-crystal synchrotron X-ray diffraction data were measured at 150, 200 and 295 K for beta-Si3N4, silicon nitride, at a wavelength of 0.7 A. The true symmetry of this material has been the subject of minor controversy for several decades. No compelling evidence favouring the low-symmetry P6(3) model was identified in this study.

A synchrotron X-ray study of triclinic LiCa2Nb3O10 with perovskite-type slabs.

The triclinic superstructure of a small crystal of LiCa(2)Nb(3)O(10), lithium dicalcium triniobium decaoxide, has been investigated by synchrotron X-ray diffraction. The unit cell is an almost rectangular parallelepiped, although there is a 0.245 degrees offset from orthogonality for beta. The structure essentially belongs to a homologous series of Li[Na(n-3)Ca(2)Nb(n)O(3n+1)] with n = 3, where the moiety in square brackets has a perovskite-type slab structure. The superstructure has a doubled unit-cell volume with respect to the tetragonal aristotype. The NbO(6) octahedra are rotated about axes parallel to [110] by approximately 10 degrees. Adjacent slabs are connected by Li atoms and are geometrically related by 4(2) pseudosymmetry lying parallel to c. There are twice as many sites as Li atoms, providing a variation of population at these Li sites.

Monoclinic superstructure of SrMgF4 with perovskite-type slabs.

Crystals of Ce-doped SrMgF4, strontium magnesium tetrafluoride, have been found to have a monoclinic P2(1) structure with doubled a and tripled c cell lengths compared with the orthorhombic Cmcm structure previously reported in the literature. The perovskite-type slabs, composed of corner-sharing MgF6 octahedra and Sr atoms, are stacked along the b axis. The six crystallographically independent MgF6 octahedra are rotated so as to provide long periodicities along a and c. The coordination numbers and bond distances around the six crystallographically independent Sr atoms are slightly different in each case. In the superstructure, the Sr atoms lie on local mirror planes which are thought to originate at the high-temperature phase transition.

Synchrotron X-ray study of Er3Al5O12 and Yb3Al5O12 garnets.

Structure factors for Er(3)Al(5)O(12) and Yb(3)Al(5)O(12) garnets were measured using focused synchrotron X-radiation, with lambda = 0.7500 (2) and 0.7000 (2) A, respectively. The difference electron density maps for Er(3)Al(5)O(12) and Yb(3)Al(5)O(12) were similar, as expected. This was attributed to the 4f electrons being shielded, which reduces their effectiveness in chemical bonding and the relative position of the rare-earth atoms in the periodic table. The symmetry of the difference electron density around the rare-earth atoms was found to reflect that of the cation geometry, emphasizing the importance of second nearest-neighbor interactions. This is consistent with the view that oxide-type structures may be regarded as a packed array of cations with anions in the interstices.

Synchrotron X-ray study of the electron density in RFeO3 (R = Nd, Dy).

Structure factors for small hydrothermally grown orthorhombic neodymium and dysprosium iron oxides RFeO(3) (R = Nd, Dy) were measured with focused lambda = 0.84 Å synchrotron radiation using a fast avalanche photodiode (APD) counter. Higher symmetry in the deformation electron density (Deltarho) maps reflects the coordination of the magnetic atoms in the structure and implies that Deltarho is sensitive to the cation-cation magnetic interactions. Within a given compound the local Deltarho topographies around the R and Fe atoms are similar, but differ markedly between compounds. The difference in Deltarho near the Nd and Dy atoms is associated with the different type of spin reorientation transitions in these compounds. The R-Fe magnetic interactions determine the magnetic phase transitions and consequently affect the electron distribution. Synchrotron radiation diffraction imaging of the electron density provides an additional tool for probing the magnetic properties of materials.

Solution and refinement of the crystal structure of Bi7Ta3O18.

The structure of heptabismuth tritantalum octadecaoxide, Bi(7)Ta(3)O(18), has been solved and refined using single-crystal X-ray diffraction data collected at a synchrotron source in conjunction with unit-cell and symmetry information derived from electron diffraction. The space-group symmetry is triclinic C1 but is very close to monoclinic C2/m. A twin component observed during data collection was successfully modelled in the refinement. The C2/m prototype fitted all the Rietveld-refinable features of a medium-resolution neutron powder diffraction pattern. The metal-atom array is approximately face-centred cubic (fluorite type), punctuated by regularly spaced displacement faults perpendicular to the [111](fluorite) direction every 2.5 fluorite unit cells. The metal-atom populations and O-atom positions are fully ordered. The Ta(5+) cations are octahedrally coordinated, with TaO(6) octahedra forming columns. The remaining O atoms occupy distorted fluorite positions. The Bi(3+) cations occupy octahedral, square pyramidal or trigonal prismatic sites within the O-atom array; strain in the latter coordination environment appears to be responsible for the lowering of symmetry from monoclinic to triclinic.

The crystal structure of Ca7Zr7Ta6O36 refined using synchrotron-radiation data.

Single-crystal X-ray diffraction data [synchrotron radiation; lambda = 1.2682 (4) Å] are used to solve and refine the crystal structure of heptacalcium hexatantalum heptazirconium hexatriacontaoxide, Ca(7)Zr(7)Ta(6)O(36). The structure adopts space group Fddd with cell dimensions a = 36.394 (1), b = 7.3674 (5), c = 31.006 (2) Å. The structure was solved by direct methods. Refinement using 1299 unique reflections leads to final values of R = 0.031 and wR = 0.034. The refined metal-atom ordering scheme is far from fully ordered and reminiscent of the A/B metal-atom ordering characteristic of the pyrochlore structure type. Bond-valence sums are calculated to confirm the plausibility of the crystal chemistry of Ca(7)Zr(7)Ta(6)O(36).

Synchrotron X-ray analysis of the electron density in HoFe2.

Structure factors for a small holmium diiron HoFe(2) Laves crystal were measured with focused lambda = 0.75 Å synchrotron X-radiation using a fast avalanche photodiode (APD) counter. The deformation electron density (Deltarho) maps are remarkable for significant excess electron density midway between the Ho atoms, which is not dissimilar to the peaks attributed to classic 'covalent bonding' in C and Si crystals. These residual electrons accumulate at the centres of the kagomé net hexagons and form, with the Fe atoms, a triangular lattice which is characterized by more stable magnetic order than the kagomé net. Similar peaks occur along the Ho-Fe and Fe-Fe contacts. These results confirm the hypothesis that 5d electrons of the rare-earth atoms are important in the spin-coupling mechanism for HoFe(2)-type compounds. The 5d electrons are far less localized than the 4f electrons, and considerable 5d-5d and 5d-3d orbital overlap occurs between neighbouring atoms. Aspherical electron density near the Ho nuclei can be associated with the Ho 4f subshell electrons. Strong depletions of the Deltarho near the atoms along the Ho-Ho, Ho-Fe and Fe-Fe vectors are indications of exchange repulsion. The effect of anharmonicity on the Deltarho is insignificant.

Synchrotron radiation study of yttria-stabilized zirconia, Zr0.758Y0.242O1.879.

The fluorite-related cubic structure of yttria-stabilized zirconia, Zr(0.75)(8)Y(0.24)(2)O(1.87)(9), has been studied by single-crystal X-ray diffraction using synchrotron radiation and by EXAFS. Two diffraction data sets obtained at X-ray energies of 512 and 10 eV below the Y K edge revealed that in the average structure Zr atoms are displaced from the origin of the space group Fm3;m along <111> by 0.19 Å, while Y atoms reside at the origin. Approximately 48% of the O atoms occupy the ideal position in the fluorite-type structure, while 43% of O atoms are displaced from the ideal position along <001> by 0.31 Å. The remaining 9% of O atoms are presumably sited at interstitial positions. Local structures around Zr and Y are investigated by combining the results of single-crystal X-ray diffraction and EXAFS studies.

Synchrotron X-ray imaging of the electron density in RFeO3 (R = Y, Ho) using an APD detector.

Structure factors for small hydrothermally grown yttrium and holmium orthoferrites, RFeO(3) (R = Y, Ho), were measured with focused synchrotron radiation at wavelengths of 0.70 and 0.84 A using both scintillation and high-speed avalanche photodiode (APD) detectors. Resulting APD Deltarho images showed striking correlations between aspherical electron densities around Fe and rare-earth metals. Approximate high symmetry in the Deltarho images indicates that cations deform the electron density far more strongly than the O atoms. The Ho-Fe magnetic interactions appear to affect the electron density distribution of the Fe atoms and the magnetic phase transitions. Space group Pnma, orthorhombic, YFeO3 (APD): Mr = 192.76, a = 5.5931 (3), b = 7.6102 (4), c = 5.2806 (3) A, V = 224.77 (2) A(3), Z = 4, Dx = 5.695 Mg m(-3), mu(0.84) = 15.56 mm(-1), F(000) = 356, T = 293 K, R = 0.045, wR = 0.073, S = 4.83 (9) for 1282 unique reflections; HoFeO3 (APD): Mr = 268.78, a = 5.5922 (3), b = 7.6157 (5), c = 5.2798 (3) A, V = 224.86 (2) A(3), Z = 4, D(x) = 7.939 Mg m(-3), mu(0.84) = 61.98 mm(-1), F(000) = 356, T = 293 K, R = 0.036, wR = 0.037, S = 3.07 (6) for 1284 unique reflections.

Selective en bloc resection of osteoid osteoma of the superior articular process of the sacral spine. A case report.

Selective en bloc resection of an osteoid osteoma from the superior articular process of the sacral spine was performed, sparing the facet joint. Computed tomography was very useful, both in making a diagnosis and in facilitating precise planning of the operative procedure. The paraspinal approach readily facilitated complete excision of the tumoral nidus with minimal surgical dissection.

[Experimental study of hyperostosis induced by hypervitaminosis A].

Radiological and histological studies were made on retinoid-induced hyperostosis in rats. Vitamin A (VA) was administered intraperitoneally in rats for 6 months. Hyperostosis was observed in 94 percent of rats administered VA and in 38 percent of the control. Chondrocytes and vascular proliferation were observed in the attachment of the tendons and in the anterior corner of the vertebral body after 3 months. Hyperostosis was observed as osteophytes in the attachment of ligaments or tendons and as heterotopic ossification in the tendons or the joint capsules of the whole body after 6 months. Immature cells were observed around the osteophytes. These areas were stained with pH 4.1 toluidine blue and disappeared following streptomyces hyaluronidase treatment. This would indicate that hyaluronic acid increased around these areas. These results appear to demonstrate that hypervitaminosis A is capable of producing hyperostosis.