Pressure-induced amorphism silicon

The high pressure Raman spectroscopy study of Ba24Siioo by Shimizu et al. [107] showed evidence for two structural transitions. The first occurs between 3.9 and 6.5 GPa and is characterized by the splitting of the 126 cm Raman mode along with a general decrease of the intensity of the modes associated with vibrations of Ba atoms. The second transformation at 20.7-23.2 GPa is associated with the disappearance of all the observable Raman features, and this was initially attributed to a pressure-induced amorphization. However, subsequent X-ray diffraction studies showed that the transition at 23 GPa in fact corresponds a volume collapse similar to Type I silicon clathrates MgSi4g [108]. 

Evidence for a pressure-induced amorphous-amorphous transition in silicon was first shown by Deb et al. [20], These authors studied porous silicon—7T-Si (silicon having nano-porous holes in its microstructure and a large surface to... 

Ikeda T, Kobayashi T, Takata M, Takayama T, Sakata M (1998) Charge density distributions of strontium titanate obtained by the maximum entropy method. Solid State Ion 108 151-157 Imai M, Mitamura T, Yaoita K, Tsuji K (1996) Pressure-induced phase transition of crystalline and amorphous silicon and germanium at low temperatures. High Pressure Res 15 167-189... 

S. K. Deb, M. C. Wilding, M. Somyazulu, and P. F. McMillan, Pressure-induced amorphisation and an amorphous-amorphous Uansition in densified porous silicon. Nature528-530 (2001). 

Direct optical observation and electrical resistance measurements carried out on amorphous silicon by McMillan and coworkers [28] showed that the HDA is highly reflective and LDA is nonreflective (see Fig. 5). From the electrical resistance measurements, the authors found that there is an abrupt decrease in resistivity across the LDA-HDA transition around P = GPa, indicating transformation to metallic HDA. The sample was verified to be in its amorphous state (using Raman spectroscopy), since pressure-induced crystallization to j8-Sn phase could also lead to a drop in resistivity. 

M. Imai, T. Mitamura, K. Yaoita, and K. Tsuji, Reversible phase transition from amorphous state to crystal induced by pressure in silicon-germanium alloys., in Proceedings of the IVInternational Conference on High Pressure in Semiconductor Physics, D. S. Kyriakos and O. E. Valassiades, eds. 1990, pp. 2, 21,82,91. 

When silicon oxide imdergoes a polymorphic transformation, associated the pressure and temperature induce the formation of clinopyroxene in microvolrrmes. A sufficiently high-pressure force on crystalhtes of clinopyroxene will lead to intense amorphization. When Na and Ca2 are amorphised, they are pushed out of the matrix, and the effect of temperature will lead to the early melting of microparticles, initiating the decomposition of alurrrinosilicate tetrahedra. 

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