Amorphous chemical short-range ordering

Although it is formally possible to extend eqn. (2) to calculate dipolar M2 values for amorphous systems by converting the summation for N finite inequivalent sites to an integral in limit N < , it would be very difficult to properly include chemical short range order (CSRO) contributions in these calculations which are already quite complex if... 

Laridjani and Sadoc (1981) studied amorphous Gd-Y alloys in the composition range 10 to 90 at% Y by X-ray diffraction. The amorphous alloys were prepared by sputtering onto an aluminum substrate at 78 K under argon pressure. Uniform foils having a thickness of 5 to 10pm were obtained. A chemical short-range order was indicated by the interference and radial distribution function. These authors found that the radial distribution function could be accounted for by a mixture of tetrahedra and octahedra. At low concentrations of Y in Gd or Gd in Y there were four tetrahedra for one octahedra, but the number of tetrahedra increased as the concentration approached an equiatomic mixture of yttrium and gadolinium. 

The electrical properties of semiconductors depend on the perfection of the crystal structure and the nature of the impurities it contains. However, the decisive factor responsible for semiconductor properties is the short-range order. By this is meant the symmetry of the electron shells, the valence an es, the interatomic distances, etc., i.e., the nature of the forces of the chemical interaction between the atoms. This is indicated by the fact that the semiconducting properties of many crystalline semiconductors are retained after melting [1] and also by the existence of a large number of liquid, amorphous, and glassy semiconductors. 

In this approach the amorphous soUd is supposed to consist of an infinite, non-perioical, three-dimensional array of interUnked atoms in which the short-range order about each atom is imposed by the same characteristics of the chemical bond as in the crystal. 

The characterization of amorphous semiconductors is further compU-cated by the fact that the same chemical composition can exist in many structural states which depend on the thermal history and preparational variables. Moreover, compositional heterogeneity, voids, cracks, as well as the preservation in some materials of molecular structures with relatively extended short-range order makes real amorphous materials quite different from the ideal disordered systems presently studied by theorists. 

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