Novel High Temperature Raman Spectroscopic Techniques, Spectral Calculation And Their Application In Micro-structure Study Of Inorganic Materials

Micro-structure study and relative science and technology development are new growth of subject and headspring of new materials in basic and applied study among crossed fields of physics and materials sciences. Micro-structure study can discover the relationship between micro-structures of materials and their macro properties. According to this, micro-structure design can be introduced to meet the requirement for realizing and improving specific functions of various materials with the enhancement of advanced experimental techniques, and the physical and chemical processing and special mechanism can be revealed.Study of micro-structure under high temperature, especially for melts, have brought much attention and recognition in the fields of metallurgy, geology, crystal growth, spectroscopy and computational chemistry and have made achievement in the past. In this paper, experimental methods of X-ray diffraction (or scattering), nuclear magnetic resonance and Raman spectroscopy, as well as theoretical methods of quantum chemistry, molecular simulation and relative coupling methods are reviewed. The rationales and their characteristics of various researching method are introduced, their advantages and deficiencies are also evaluated as consideration for this study. Raman spectroscopy is chosen as predominant experimental method because of its potentials in application under high temperature, while quantum chemistry and other methods being applied for theoretical explanation.High temperature micro-Raman spectrometer (up to 1623 K) is constructed by using Leitz microscopic heating stage and argon ion laser (lines, 514.5 and 488.0 nm) coupled with Olympus BH-2 microscopy and mono channel scanning based on JY U1000 monochromator in Shanghai Enhanced Laboratory of Modern Metallurgy and Material Processing in Shanghai University. High temperature macro-Raman spectrometer (up to 2023 K) is also constructed by using pulsed laser (copper vapor laser or semi-conductor laser) and time resolved detecting technique. With the help of these techniques, dense background thermal radiation can be satisfactorily eliminated in routine Raman spectra recording. Furthermore, a novel high temperature Raman spectroscopic technique combined with accumulated time and space resolved method is realized by coupling intensified charge coupled device (ICCD) with visible pulsed laser.Silicates are most abundant substances on the earth, involved with domains of metallurgy, glass, ceramic and geologic magma, and micro-structure study about silicates is most significantly important. In this paper former efforts of studies on micro-structure of silicates were summarized. A series of typical silicate clusters with characteristic structure are designed, and they are optimized in geometric configuration, and made Raman spectrum simulation by using quantum chemistry ab initio calculation method. A new concept of stress index of silicon-oxygen tetrahedron (SIT) is defined and applied to correlate the vibrational wavenumber of non-bridging oxygen symmetric stretching of silicon-oxygen tetrahedron with the value of SIT. This helps to understand local stabilized micro-structure affected by geometric and electron structure, and strengthens the representation, characteristic and application of Raman spectra of silicate. It demonstrates that various Raman spectra of silicates can be satisfactorily elucidated, especially for the understanding of non-symmetry of partial Raman spectra of primary structure of silicates. It also helps to explain characteristics of silicate melts while temperature coefficient is introduced.Cation effect on micro-structure and its Raman spectrum of silicate cluster is investigated by experimental and theoretical calculation for alkali silicates. It shows that the local micro-structure configuration has little been influenced, the vibrational wavenumber of non-bridging oxygen symmetric stretching of silicon-oxygen tetrahedron has also no distinct deviation, but the cross section of Raman optical active vibration is dramatically affected. Cation with larger radius can enhance the covalent component of non-bridging oxygen bonding which is the key point for increasing Raman optical activity as confirmed by electron structure calculation. Meanwhile, other spectral effects such as neighbor enhancement, which means that Raman optical activity of non-bridging oxygen of primary Q₃ species will be enhanced by neighboring Q₄ species, can also be understood.Temperature dependent Raman spectra of alkali and alkali earth silicate crystals, and Raman spectra of silicate glasses as well as their melts demonstrate that Raman spectra have the advantage of delicate structure resolution and characteristics for high temperature in-situ recording and investigation, especially for the research of temperature dependent structure transformation. Although high temperature Raman spectra of silicate melts have lower signal-noise ratio, it reflects the fact and the nature of multiple cluster species coexisted. Deconvolution of Raman spectra of silicate melts can be used to diagnose micro-structure units and investigate temperature dependent varieties of them, as helps to establish a basement for communicating micro-structure and its property of silicate.Self developed high temperature Raman spectroscopic techniques are also applied to record various materials in the fields of metallurgy, crystal growth, glass chemistry, geology and functional materials, including inorganic polymers (phosphates and borates), molten salts (nitrates and carbonates), functional ceramics, nano materials and relative processing, as well as in-situ investigation of crystal growth. It is concluded that high temperature Raman spectroscopy is a powerful tool for phase diagnosis and micro-structure investigation of various materials, and also offer experimental possibility and convenient to penetrate the micro-structure of substances and their melts under high temperature, especially during materials processing such as micro-structure of boundary in crystal growth. Temperature and chemical composition dependent micro-structure deviation and its rule on atom or molecular level can be explored and discovered. Those results vice versa help to develop new manufacture techniques during new materials exploring. With the help of related experimental and calculation method, the obtained experimental Raman spectra are well annotated and elucidated, which deepen one's knowledge of micro-structure units of substances and establish a good basement to correlate macro-properties with their micro-structures.