You Jing-Lin

Temperature Dependence of the Raman Spectra and Phase Transition of Zirconia

A newly constructed high-temperature Raman spectrometer was used to study the temperature-dependence Raman spectra (up to 2023 K) and transformation of zirconia crystal. High-temperature Raman scattering is a useful tool in characterizing the different structures of zirconia and offers the possibility of identifying the phase transformation. It shows that monoclinic zirconia transforms to tetragonal phase at about 1440 K during the process of increasing temperature, but shows a lower transformation temperature from tetragonal to monoclinic phase at about 1323 K while the temperature decreases.

Temperature Dependence of the Raman Spectra of Na2Si2O5

The microstructures of Na2Si2O5 from room temperature up to 1773 K are studied by high-temperature Raman spectroscopy. Deconvolutions of complex Raman spectra of crystal and amorphous states (glass and melt) are described. The results show that the temperature-dependent Raman spectra clearly indicate phase transition. The relative abundance of various kinds of SiO4 tetrahedrons (each Si binding to different numbers of bridging oxygens) can be qualitatively and quantitatively resolved as to be varied obviously with different temperatures. This shows that high-temperature Raman spectroscopy provides a useful tool for microstructure research under high temperature and helps to explain the properties of silicate glasses and melts.

High temperature Raman spectroscopic study of the micro-structure of a caesium triborate crystal and its liquid

Raman spectra of a caesium triborate (CBO) crystal at different temperatures up to the melting temperature have been recorded. All of the peaks of corresponding to the crystal broaden and decrease in wavenumber with increasing temperature. The vibrational modes of the CBO crystal, in which the basic structural unit is the triborate group (B3O7)5−, have been simulated using a plane-wave pseudopotential method. An isomerization reaction from four-coordinated boron to a three-coordinated species was observed during the melting process. The continuous three-dimensional network of the crystal collapsed and transformed into spiral chains that consist of (B3O6)3−groups during the melting process. Detailed spectral analysis is also competently explained by applying quantum chemistry ab initio calculations.

Raman Spectrum Analysis on the Solid–Liquid Boundary Layer of BGO Crystal Growth

We study the Raman spectra of Bi4Ge3O12 crystal at different temperatures, as well as its melt. The structure characters of the single crystal, melt and growth solid–liquid boundary layer of BGO are investigated by their high-temperature Raman spectra for the first time. The rule of structure change of BGO crystal with increasing temperature is analysed. The results show that there exists [GeO4] polyhedral structure and Bi ion independently in BGO melt. The bridge bonds Bi–O–Bi and Bi–O–Ge appear in the crystal and at the boundary layer, but disappear in the melt. The structure of the growth solid–liquid boundary layer is similar to that of BGO crystal. In the melt, the long-range order structure of the crystal disappears. The thickness of the growth solid–liquid boundary layer of BGO crystal is about 50 μm.

Phase Transformations and Melt Structure of Calcium Metasilicate

The β → α phase transition, melting, crystallization, and vitrification of calcium metasilicate were studied by high-temperature Raman scattering spectroscopy. The results demonstrate that, in the course of melting, the [Si3O9] metasilicate rings, which form the structural basis of the α phase, transform mainly into [SiO3]∞ anions. The structural similarity or dissimilarity of the CaO · SiO2 melt to crystalline phases is shown to have a crucial effect on its crystallization/vitrification behavior.

Temperature-dependent Raman spectra and microstructure of barium metaborate crystals and its melts

We have measured the Raman spectra of β- and α-barium metaborate in crystal and liquid states from room temperature to 1873 K, with a semiconductor laser as the laser source, coupled with a time-resolved detection system to eliminate the dense thermal emission background when temperature was considerably high. Temperature-dependent Raman spectra can clearly indicate that the phase transformation from β- to α-barium metaborate has been completed during 1273-1300 K. Variations of different kinds of microstructure units with temperature are identified and discussed.

Coordination properties and structural units distribution of Q T i in calcium aluminosilicate melts from MD simulation

The distribution of Al(j) and the structural units distribution of QTi in calcium aluminosilicate melts were studied by means of molecular dynamics simulation. The results show that provided there exists lower-field strength cation relative to Al3+, such as alkaline and alkaline earth metals, Al will be four-coordinated but not six-coordinated. Meanwhile, if there exist a large number of higher-field strength cations such as Si4+ and little lower-field strength cation, six-coordinated aluminum will be formed. The relation of structural units distribution of QTi with chemical composition shift was also extracted, showing that as Ca2+ exists, the distributions of QSii, QAli or QTi have the similar changing trend with the variation of component. Because of high-temperature effect, the Al-tetrahedral units in melts are greatly active and unstable and there exist dynamic transforming equilibria of Al(3) ⇋ Al(4) and Al(5) ⇋ Al(4). The three-coordinated oxygen and charge-compensated bridging oxygen are proposed to explain phenomena of the negative charge redundancy of AlO4 and location of network modifier with charge-compensated function in aluminosilicate melts.

An Ab-Initio Calculation of Raman Spectra of Binary Sodium Silicates

Raman spectra of binary sodium silicates are calculated by self-consistent field (SCF) molecular orbital ab initio calculation of the quantum chemical method with several poly silicon–oxygen tetrahedral model clusters when both the basis sets of 6-31 G and 6-31 G(d) are applied. The symmetric stretching vibrational frequency of non-bridging oxygen in a high frequency range and its Raman optical activity and scattering cross section are deduced and analysed. The correlation between this vibrational Raman shift and its microscopic environment of the silicon–oxygen tetrahedron is found based on interior stress of configuration, which depends on the connecting topology of adjacent silicon–oxygen tetrahedra (SiOT). A newly established empirical stress index of tetrahedron is introduced to elucidate the above relationship.

A new method for the Raman spectra calculation of vitreous or molten silicate

A new method is deduced to calculate the Raman spectra of vitreous or molten silicate. This method includes five steps: (i) molecular dynamics simulation to generate thousands of vitreous or molten configurations in equilibrium; (ii) decomposing the configurations into five kinds of defined tetrahedral units; (iii) normal vibrational analysis with Wilsons GF matrix method for the eigenfrequencies and eigenvectors of each tetrahedral unit; (iv) Raman intensity calculations for each vibrational mode by utilizing the electro-optical parameter method and bond polarizability model; (v) accumulating the data of frequencies and corresponding intensities to form the partial Raman spectral line of each defined tetrahedral unit and finally the envelope.

Investigation of the Cr:LiSrAlF6 crystal by high-temperature Raman spectroscopy

In this paper, Cr-doped LiSrAlF6 crystals are investigated using high-temperature Raman spectroscopy and the single-crystal Raman spectra of Cr:LiSrAlF6 are analysed by factor group theory and comparison with other fluorides. The results indicate that Cr:LiSrAlF6 is stable below its melting point; Raman peaks located at 561, 322 and 250 cm−1 are assigned to the A1g modes of AlF6, SrF6 and LiF6 octachdra, respectively; with temperature increasing, Raman peaks associated with AlF6 octahedra shift towards low frequencies, while LiF6 and SrF6 octahedra are temperature-insensitive; around the crystal melting point, three new Raman peaks occur, which are associated with the AlF6 octahedral chain structure. Finally, the microstructural evolution of Cr:LiSrAlF6 from room temperature to its melting point is discussed based on its Raman spectra.