Amorphous Solids, Glasses

It is interesting that structural, mechanical and electronic properties in chalco-genide glasses (As-Se, Ge-S, Ge-Se, Ge-As-S) change monotonically with composition, but at N = 2.67 a sharp change in properties occurs, indicating a phase transition from two- to three-dimensional lattice [47, 48], This phenomenon can be described as amorphous morphotropy . 

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In the non-crystalline or amorphous solids (glasses and polymers) an arrangement of atoms in a lattice with a periodic order does not exist. 

X-ray scattering structural studies of very small single crystals, phase transition in powders, local order in amorphous solids, glasses. . . ... 

This method provides unvaluable informations on the short and medium range order in disordered atomic architectures amorphous solids, glasses but also liquids or complexes in solution. The fast development and the economical importance of... 

A distinctive class of amorphous solids are glasses, which are defined (Morey, 1954) as amorphous solids obtained from the melt (solidification of a liquid). This distinction between glasses and other amorphous solids may appear pedantic. However, it is intuitively pleasing to consider an amorphous solid (glass) obtained by cooling a liquid to be both structurally and thermodynamically related to that liquid. The connection between an amorphous solid produced, for example, by extensive plastic deformation of a crystal, and other states of the material is more tenuous. 

A large class of amorphous solids — glasses — have been studied extensively over many decades from the point of view of their thermodynamical and structural properties. The first two chapters deal with this aspect which is considered essential for any deeper understanding of the nature of the amorphous state. The inherent metastalpility of the amorphous state compared to the crystalline state is responsible for many discrepancies in the experimental results. It should be understood not only for improving the reproducibility of the measurements but also because the control of the structural parameters is the heart of such applications of amorphous semiconductors which cannot be produced by devices constructed of crystalline materials. Indeed, most kinds of memory devices are based on the ability of glasses to exist in different structural states. 

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