Raman spectra of binary sodium silicates in various components were calculated by the self-consistent field molecular orbital ab initio calculation quantum chemical (QC) method with several polysilicon-oxygen tetrahedral model clusters with both 6-31G and 6-31G(d) basis sets being applied. Relevant pure anion clusters were also be calculated in order to determine the cation effect by comparison with the available sodium series. High and intermediate Raman-active wavenumber ranges were especially considered. The symmetric stretching vibrational wavenumber of non-bridging oxygen (NBO) in the high-wavenumber range and its Raman scattering cross-section were deduced and analyzed. Several synthesized binary sodium silicate crystals were measured for comparison. The correlation between the vibrational Raman shift and the microscopic environment of the silicon-oxygen tetrahedron (SiOT) was found based on interior stress of configuration or superstructure, which depends on the connecting topology of adjacent SiOTs. A newly established empirical stress index of a tetrahedron (SIT) was introduced to elucidate the above relationship. A new notation of SiOT accompanied by superstructure information was proposed and used to describe the practical and delicate types of SiOT in various states of binary sodium silicates. The Raman scattering cross-section of the symmetric stretching vibration of NBO shows a roughly decreasing relationship with SIT or the Raman shift in the high-wavenumber range only under the circumstance of equivalent linkage between SiOTs, and Raman optical activity (ROA) enhancement ofQ 3 species occurs with Q 4 species as its nearest neighbor, which indicates the electronic coupling between them. It was also demonstrated that the Si-O b -Si bending vibrational Raman shift in the intermediate wavenumber range shows a monotonic decreasing relationship with the value of the Si-O b -Si angle while other minor impacting factors remains unknown. This work offers basic information on the superstructure of binary sodium silicates and its relationship with characteristic vibrational Raman spectra, which can be widely applied in qualitative and quantitative studies of the microstructure of silicates.

Liquid Al 2 O 3 has been supercooled more than 500 K below its melting point (T m = 2,327 K) using aerodynamic levitation and laser heating techniques. High energy synchrotron x-ray measurements were performed over a temperature range of 1,817 ≤ T (K) ≤ 2,700 and stroboscopic neutron diffraction at 1,984 and 2,587 K. The diffraction patterns have been fitted with Empirical Potential Structure Refinement (EPSR) models and compared to classical Molecular Dynamics (MD) simulation results. Both sets of models show similar trends, indicating the presence of high populations of AlO 4 and AlO 5 polyhedral units predominantly linked by triply shared oxygen atoms. EPSR reveals that the mean Al-O coordination number changes linearly with temperature with n AlO = 4.41-[1.25 × 10 −4 ] (T-T m), with a 2.5 Å cutoff. Both EPSR and MD simulations reveal a direction of the temperature dependence of the aluminate network structure which moves further away from the glass forming ideal (n AlO = 3) during supercooling. Furthermore, we provide new experimental data and models for amorphous alumina grown by sequential infiltration synthesis of a polymer template. The amorphous solid form likely has a larger Al-O coordination number than the liquid, consistent with expectations for the hypothetical glass.

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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.

The structure of the melt near a crystal-melt interface is a fundamental problem in the dynamics of crystal growth. In this work, high-temperature Raman spectroscopy was used to investigate the melt structure near the CsB 3 O 5 (CBO) crystal-melt interface. An ordered boundary layer was observed near the interface; its thickness is larger than 100 µm. An isomerization reaction between 3-and 4-coordinated boron was found in the layer. The ordering of the melt is strongest near the crystal-melt interface and decreases toward the bulk melt. These results have been applied to explain the growth habit of CBO crystal. The predicted growth habit is in good agreement with the observed result.