A Raman Spectroscopy Study Of Hyperfine Structure Of Aluminosilicate And Feldspar

Ab initio calculation method of quantum chemistry was used to optimize several typical sodium aluminosilicate model clusters and calculate their Raman frequencies under restricted Hartree-Fock method 6-31G(d) basis sets. Considering the effect of aluminum-oxygen tetrahedron,SIT (Stress Index of Tetrahedron) was promoted to describe the microstructure of sodium aluminosilicate and the symmetric stretching vibrational frequency of non-bridging oxygen in the high and intermediate frequency range were deduced and analyzed. It was shown that the symmetric stretching vibrational frequency of non-bridging oxygen in the high frequency range depends closely on environmental hyperfine micro-structure Q_{i(m1h,m2q,m3t…)}⁽n₁n₂…n_k(n_k+1…n_i)).It was found that the symmetric stretching vibrational frequency of non-bridging oxygen in the high frequency range large enhanced while SIT increasing. Vibrational modes for the most prominent peaks, between 700-800cm^-1, are dominated by Al-Onb symmetric stretching vibrations, and the vibration frequency are relatively stable. It was also demonstrated that the Si-O_b-Si(Al) bending vibrational Raman shift in the intermediate wavenumber range shows a decreasing relationship with the value of the Si-O_b-Si(Al) angle.The Raman spectra of alkali feldspars have been studied in order to seek a new way to solve the problem in measuring the alkaline feldspars'ordering degrees. With the alkali feldspars'ordering degrees increasing, more bands were observed in the low-frequency and mid-range regions in the Raman spectra and the relative intensity of those bands were increasing too. The band near 480cm^-1 was divided into two bands which near 480cm^-1 and 450cm^-1,and the ratio of those relative intensity were sensitive to the change of the ordering degree of alkali feldspar.Raman spectra of plagioclase show that aluminum-oxygen tetrahedron SIT (Stress Index of Tetrahedron) decreases with the increasing anorthite(An) compotent and the ratio of Al/Si, therefore the bands within the high range shift to lower.The ordering degree of Plagioclase changed while the compotent An increasing, generally,the end-member of plagioclase series has high ordering degree and mid-member has lower ordering degree. The component of An exhibits a linear ralationship on frequency of the band near 560cm^-1, and deduce out plagioclase component and the frequency relational expression from this: An = 4*(577.6-ν).The in-situ high temperature Raman spectra of albite; microcline and synthetic leucite glass have been determined. The Si(Al)-O bond lengths increase with increasing temperature, thus cause raman peak within the range of high frequency shift to lower.The increasing temperature increased the distribution of angle of Si(Al)-O-Si bridging oxygen,and which broadens the full width at a half maximum(FWMH) of bands in mid-range; Aluminium atom were in four-coordinated in crystalline feldspar,glass and melt;The structures of feldspar glasses and melt are probably based on interconnected six-membeed rings.