Newsletter

search results

results of search on CRYSTALLOGRAPHY JOURNALS ONLINE

10 citations found for Ohtaka,

Search for Ohtaka, in the World Directory of Crystallographers

Select bibliographic records for downloading using the checkboxes or select all button

Results 1 to 10, sorted by name:


Download citation
Download citation

link to html
Single crystals of Ni3(Al, M) were grown by the Bridgman method, where M is Ti, V, Cr, Mn, Fe, Nb, Mo and Ta. The composition was controlled to be about Ni75Al20M5 so that the alloying element, M, substitutes mainly for Al. With these crystals conventional X-ray structural analysis was performed. The measured static displacements of atoms from the average lattice points depended largely on the alloying elements and varied in the range 0.00-0.13 Å for Ni atoms and 0.09-0.18 Å for Al atoms. It was found that these atomic displacements correlated well with the atomic radius of the alloying element, M. For example, when the atomic radius of M is larger than that of Al, the static displacements are large for the atoms in the Al sublattice but small for the atoms in the Ni sublattice. By contrast, when the atomic radius of M is smaller than that of Al, the displacements are more enhanced in the Ni sublattice than in the Al sublattice. Thus, there is an interesting correlation between the atomic displacements in both the Al and Ni sublattices in the presence of alloying elements. This seems to be one of the characteristics of alloyed compounds with several sublattices.

Download citation
Download citation

link to html
The crystal structure of the low-temperature (LT) modification of LaBO3 has been redetermined from single-crystal X-ray data; the resulting structure confirms the previous study [Abdullaev, Dzhafarov & Mamedov (1976). Azerbaidzhanskii Khim. Zh. pp. 117–120], but with improved precision. LT-LaBO3 crystallizes in space group Pnma and adopts the aragonite-type structure. Except for one O atom, which is situated on a general position, all other atoms (one La, one B and a second O atom) lie on mirror planes. The structure is composed of LaO9 polyhedra with an average La—O distance of 2.593 Å and trigonal BO3 groups with an average B—O distance of 1.373 Å. Slight anisotropies of the thermal vibrations of La and B atoms suggest that the electrostatic La...La and La...B inter­actions across the shared edges are weak.

Download citation
Download citation

link to html
The high-pressure phase of SrGeO3 synthesized at 6 GPa and 1223 K adopts the ideal cubic perovskite-type structure. The Ge-O bond is largely covalent, which influences the thermal vibration behavior of the O atom.

Download citation
Download citation

link to html
A new strontium germanate, SrGe2O5, was crystallized at 6 GPa and 1223 K. The effect of cation size on the crystal structure is discussed in terms of bonding nature.

Download citation
Download citation

link to html
Single crystals of LaAlO3 (lanthanum aluminium trioxide) have been synthesized at 4.5 GPa and 1273 K, in the presence of an NaCl + KCl flux. The compound crystallizes with the cubic perovskite structure (space group Pm\overline{3}m). The thermal vibration of the O atom is remarkably suppressed in the directions of the Al-O bonds, and this anisotropy ranks among the largest observed in stoichiometric cubic perovskites.

Download citation
Acta Cryst. (2014). A70, C1112
Download citation

link to html
Hydrogarnets, represented by hydrogrossular, are produced by the replacement of (ZO4)4- in garnets by (H4O4)4- (Z: tetrahedral cation) and the vacancies of tetrahedral cations are created by this replacement. Most of reported hydrogarnets crystallizes with cubic symmetry (space group Ia-3d). To our knowledge, Ca3Mn2[SiO4]2.07[H4O4]0.93 with space group I41/acd (tetragonal) [1] has been only reported as a low-symmetry hydrogarnet. In the cubic hydrogarnets, all O atoms are crystallographically equivalent, whereas in low-symmetric one, they can be located at non-equivalent sites. Therefore, the investigation of low-symmetry hydrogarnes is important to gain knowledge of the site preference of H atoms. Recently, we have successfully synthesized the single crystal of a new low-symmetry hydrogarnet CaGe0.924O3H0.304 (= Ca3(CaGe)[GeO4]2.696[H4O4]0.304) with tetragonal space group I41/a, at 3 GPa and 1273 K under the presence of H2O component. This tetragonal hydrogarnet is produced by the partial replacement of (GeO4)4- in high-pressure CaGeO3 garnet, Ca3(CaGe)[GeO4]3, by (H4O4)4-. In the present study, we report the single crystal X-ray diffraction study of this hydrogarnet at 98 and 298 K. In the structure refinement at 298 K, the occupancy parameters resulted in 0.393(2) for tetrahedral Z2(Ge) site, coordinated only by O6 atoms, and showed no significant deviation from 1.0 for the remaining cation sites. The bond valence sums of each atom except O6 atom agree with the valences of occupied atoms, whereas that of O6 atom are 1.50, deviating largely from oxygen valence. Thus, the substitution of OH groups for O atoms in the present sample occurs only at O6 site, which indicates that O6 is the most preferential site for the OH substitution. The position of H atom will be examined from the residual electron density distributions at a low temperature of 98 K, and the hydrogen bonding in the crystal structure will be discussed.

Download citation
Download citation

link to html
Using a large volume high pressure apparatus, quartz-type crystalline GeO2 and Li2O-4GeO2 glass have been compressed up to 14 GPa at room temperature and their local structural changes have been investigated by an in-situ XAFS method. In quartz-type crystalline GeO2, the change of the coordination number from 4 to 6 begins above 8 GPa and finishes below 12 GPa. On decompression, reversal transition begins below 8 GPa and there is a large hysteresis. Almost no sixfold coordination of Ge is preserved after releasing pressure. Change of coordination number in vitreous Li2O-4GeO2 begins above 6 GPa and is completed below 10 GPa. Reversal transition begins below 10 GPa and the hysteresis is smaller than that of quartz-type GeO2. Change of coordination number in vitreous Li2O-4GeO2 is also reversal.

Download citation
Download citation

link to html
The phase relations and equation of state of ZrO2 were investigated up to 100 GPa by means of in situ observation using laser heating in a diamond anvil cell and synchrotron radiation. In situ high-temperature experiments performed below 12.5 GPa suggest the possibility that stoichiometric ZrO2 does not show the cubic structure up to the melting temperature.

Download citation
Download citation

link to html
At 11.0 GPa the diamond-type structure changes in the high-pressure phase with an increse in coordination numbers, and prolonged bonding distances make the magnitudes of [sigma](2) larger.

Download citation
Acta Cryst. (2008). A64, C67
Download citation


Follow IUCr Journals
Sign up for e-alerts
Follow IUCr on Twitter
Follow us on facebook
Sign up for RSS feeds