This modification of Nb2Os crystallizes in the space group Pbam with unit-cell dimensions a = 6" 175 (1), b= 29.175 (4) and c= 3.930 (1) A. The structure was determined and refined by the full-matrix leastsquares method based on 725 X-ray diffraction intensities collected on a four-circle diffractometer. The conventional R value is 0-054. The unit cell contains Nb16.aO42; Dx = 5-236 g cm-3. The 16 Nb atoms lie in a sheet parallel to (001) and are surrounded by seven or six oxygen atoms forming pentagonal bipyramidal or distorted octahedral coordination polyhedra respectively. These polyhedra are joined by edge-or corner-sharing within the (001) sheet and exclusively by corner-sharing along [001]. The remaining Nb atoms occupy those interstitial sites at random which lie between the (001) sheets of the other Nb atoms and are surrounded by nine oxygen atoms. The structure is similar to but not identical with that of fl-Ta2Os,

Colloidal crystallization of poly­(vinylidene fluoride) (PVDF) nanoparticles (NPs) and its β-phase transformation were studied. The pristine PVDF NPs with an average diameter of 230 nm consist of 46% α-phase and 54% amorphous PVDF. The PVDF NPs were assembled on a quartz substrate by means of vertical deposition method from a tetrahydrofuran dispersion of PVDF NPs with a few volume percentage of n-alkane. The resultant colloidal thin films displayed a pale-greenish structural color with the selective reflection at around 550 nm wavelength due to closely packed PVDF NPs. The colloidal thin films were immersed into an acetonitrile solution containing 2 wt % ionic liquid, subsequently air-dried, and thermally annealed at 140 °C, just below the melting point of the PVDF–IL blends. After annealing, the PVDF NPs partially transformed into its β-phase with the volume percentages of α-, β-, and amorphous phases of 22, 32, and 46%, respectively. The postannealed colloidal films still maintained the face-centered-cubic assembling structure of PVDF NPs, thus displaying the greenish structural color and selective reflection.

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Abstract. Monoclinic, P21/n, a = 13.159 (12), b = 7.161 (3), c=7.499 (6) A, /?=93.76 (5) °. Z=8. Om=7"17, Dx= 7"26 g cm -3. Crystals were synthesized under high pressure at high temperature. The structure has no direct resemblance either to the scheelite-or to the wolframitetype. It consists of densely packed layers of WO6 octahedra, which are connected by edge-and corner-sharing; barium atoms are located between them. The coordination number of the barium atoms has increased in comparison with the structure under ordinary conditions.Introduction. This phase exists above the pressure P(kbar) = 26.7 + 0.0265 T (°C), (T= 600-1000 °C), and is quenchable to normal pressure (Fujita, Yamaoka & Fukunaga, 1974).The intensity data were collected on a Rigaku fourcircle diffractometer with Mo Kez (2=0.70926 A,) radiation monochromatized by graphite. In the range 20 < 90°, 6099 independent reflexions were measured, of which 3791 were considered not observed. The systematic absences were h0/, h + l= 2n + 1, and 0k0, k =

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