Structure of CaScAlSiO6-pyroxene.

Raman spectroscopic study of clinopyroxenes in the join CaScAlSiO6-CaTiAl2O6.

“…Although the change in the central wavenumbers of the Si-O-Si and the Si-O- Al stretching vibration bands is small, the central wavenumber of Lorentzian band of the Al-O-Al mode moves toward lower frequencies with increasing TiAl contents considerably. The mean T-O (br) distance was observed as 1.714 A for the ScA1 (100) pyroxene (Ohashi and Ii, 1978) and calcu lated as 1.723A for the SCAT (70) TiAl 30pyroxene based on the mean ionic radius of the tetrahedral cations (Ohashi et al, 1979). The Fig.…”

“…and Ti with 16atm% (Ohashi et al, 1979 and Table 2 is that the relative intensity of the band around 677 cm-1 decreases with an increase of CaTiA12O6 (hereafter abbreviated TiAl) contents. In Fig.…”

“…In the ABSi206 type clinopyroxenes, it was found that the Raman shifts of the Si-O-Si stretching vibration are linearly dependent on the Si-Si distance (Ohashi and Sekita, 1982). The T-T distance of the CaScAlSiO6 pyroxene is 3.186A (Ohashi and Ii, 1978). On the basis of this linear dependence of the Raman shift on the T-T distance, the Raman shift of Si-O-Si stretching vibration of the CaScA1SiO6 pyroxene can be expected to be approxi mately 620cm-1.…”

“…As for Al and Si ions, it is dif fcult to determine the degree of ordering by the X-ray diffraction technique, since Al and Si ions have nearly equal X-ray scatter ing factor. The structure refinements of CaAI2SiO6,CaFeAlSiO6,CaScAlSiO6,and Cal.OOSc0.84Ti0 .27Al1.16Si0.73O6 pyroxenes show that Al and Si ions are randomly distributed throughout tetrahedral sites in average and the aluminum avoidance rule is violated in these structures (Okamura et al, 1974;Ghose, et al, 1975;Ohashi and Ii, 1978;Ohashi et al, 1979). However, this fact does not nec essarily indicate that short-range Si/Al ordering is ruled out.…”

The correlation between the Si-O (bridging) distance and the frequency of the Si-O-Si stretching in clinopyroxenes.

“…In a clinopyroxene each tetrahedron has two (br) and two (non-br) bonds. The mean of the four Si-O distances depends mainly on the sizes of the cations occupying M1 and M2 sites (Ohashi, Fujita and Ii, 1979), and the individual Si-O distances are strongly correlated with the Pauling bond strength received by the oxygen atoms (Baur, 1971), and the electronegativity and the electronic structure of non tetrahedral cations (Ohashi, 1979). Figure 1 illustrates the variation of the frequency of the Si-O-Si stretch with the mean Si-O (br) distance in the clinopyroxenes.…”