In order to optimize the growth conditions for tungstate crystals, the structural evolution of ditungstate Na 2 W 2 O 7 from the crystalline to molten states during heating has been investigated by in-situ high temperature Raman spectroscopic technique. The experimental temperature-dependent Raman spectra showed that Na 2 W 2 O 7 crystal has not undergone any solid-state phase transformations during heating process from 298 to 1013 K. In contrast to crystalline Na 2 W 2 O 7 , in which [WO 4 ] tetrahedra and [WO 6 ] octahedra coexist, the tungsten-oxygen groups in molten Na 2 W 2 O 7 have the form of (W 2 O 7 ) 2À anion composed of two [WO 4 ] by sharing their corner oxygen atoms. To validate the structural evolution of Na 2 W 2 O 7 above, Raman activity of vibrations of Na 2 W 2 O 7 crystal and its melt were calculated using density functional theory (DFT) and compared with the in-situ Raman spectra of Na 2 W 2 O 7 . A non-crystalline phase and an intermediate state of Na 2 W 2 O 7 were obtained by rapid quenching and relatively slow cooling of the homogeneous melt, respectively.

No abstract

2008) Synthesis and characterisation of nematic liquid crystals containing a trans-decalin ring, Liquid Crystals, 35:6, 665-673To link to this article: http://dx.The synthesis and mesomorphic behaviour of a series of liquid crystals incorporating a trans-decalin ring and two aromatic rings linked by esters are reported. Structures of the new compounds were confirmed by IR, 1 H NMR, 13 C NMR and elemental analysis. A single crystal of compound 18 was prepared to confirm the transconformation of the decalin ring. Liquid crystalline properties were investigated by differential scanning calorimetry and polarising optical microscopy. All of the synthesised compounds except 17e are found to show only an enantiotropic nematic phase over a wide temperature range.