Continuous Random Network Model

Alben and Boutron suggest that the peak in the X-ray and neutron scattering functions at 1.7 A-1 is indicative of an anisotropic layer structure extending over at least 15 A in Polk type continuous random network models. To show this better Fig. 52 displays the radial distribution function of the Alben-Boutron modified... 

If the different continuous random network models of high and low temperature H20(as) are valid, the following tests are worthy of attention ... 

Clearly, any measurement that differentiates between the properties of high and low temperature forms of H20(as), and/or delineates the relationship between H20(as) and liquid H20, can be used to test the hypotheses advanced vis a vis their structures. These and the experimental tests suggested, together with the construction of continuous random network models more sophisticated than that for Ge(as), the increased use of computer simulation, and exploitation of the available experimental information to guide the choice of appproximations in a statistical mechanical theory should increase our understanding of H20(as) and, uitimately, liquid H20. 

One of the early models to describe the amorphous state was by Zachariasen (1932), who proposed the continuous random network model for covalent inorganic glasses. We are now able to distinguish three types of continuous random models ... 

This latter result should put to rest the once-expressed idea that distortions in a continuous random network model would increase as the size of the model is increased, leading eventually to such a build-up in strain as to limit the size of the model. Of course, for a hand-built model, there may well be a limit to the size. There is no way to return to the interior of a hand-built model to make rearrangements that would reduce the strain for surface atoms. 

Figure 2.06 Continuous random network model simulating the structure of amorphous Si02 (After Bell and Dean, 1966).

The simplest model of glass structure, Zachariasen s continuous random network model, represents glasses as being formed by random... 

Spitzer and Fan (1958) and Fan and Ramdas (1959) observed an absorption band in silicon at 490 cm induced by irra ation. They ascribed it to the fundamental optical mode of Si made infrared active by the introduction of lattice defects. Tauc et aL (1970a) observed a band in amorphous Ge at 270 cm and interpreted it as disorder induced one-phonon absorption (Figure 4.2). Lurio and Brodsky (1972) studied the infrared spectra of a-Ge and Si and their results were interpreted by Alben etaL (1973). They used the continuous random network model and showed that for the understanding of the relative strengths of the infrared bands the transition matrix elements must be taken into account. 

Applying Eq. (7.1) to a continuous random-network model of 216 silicon atoms proposed by Wooten et al. [250] we obtained 0.021 electron units for the rms deviation from charge neutrality. This is in reasonable agreement with recent theoretical results [251, 252], but considerably different to experimental estimates ranging from 0.1 to 0.3 electrons [253, 254]. The discrepancy with the core-level spectroscopic estimation [253] may be explained on the basis of intra-atomic charge transfer, while the infrared... 

Steinhardt R, Alben R., and Weaire D., Relaxed continuous random network models,/. Non-Cryst. Solids, 15,194-214 (1974). 

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