Amorphous atomic size factor

It has been shown that all the properties of T, Hy, 0 and electrical resistivity at room temperature (Prt) for the Al-R amorphous alloys were essentially independent of the atomic number of the R metals. The atomic size of the R metals varies systematically with the atomic number and hence the atomic size factor also seems to have little effect on the above-mentioned properties. On the other hand, it is generally known that the inherent chemical nature of the lanthanide metals results from 4f-electrons which lie at the inner side in their atoms. Although the number of 4f-electrons varies systematically with the atomic number, the electrons are screened by 5s - and 5p -electrons which lie at the outer side of the atoms, resulting in a similarity in chemical properties of the lanthanide metals. Accordingly, it may reasonably be assumed that the independence of the properties of the Al-R amorphous alloys as a function of atomic number is due to the unique electronic structure in which the 4f-electrons are screened by 5s- and 5p-electrons. 

Figure 105 summarizes the changes in the as-quenched phase and the atomic diameter in the Zn55Mg4oRs alloys with the R elements. We note a systematic change dependent on the atomic size of the R elements. The as-quenched structure exhibits the amorphous phase when it contains La, Ce, Pr or Eu, and the icosahedral phase wdien it contains Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or Y. It seems that the atomic size of the R element is an important factor for the formation of amorphous and icosahedral phases. The alloys containing an R element with an atomic diameter larger than 0.366 nm, except Yb, form... 

Biodegradable polymers accelerate the degradation of bacteria or pathogens due to the hydrophilic backbone chain of polymers which contain atoms, such as O, N, S, in the polymer chain. The amorphous nature, small size and high porosity of biodegradable polymers are the factors which disrupt the outer bacterial membrane. 

An alternative approach to the problem is the isotopic substitution method. Here one uses the same alloy prepared with different isotopes having different neutron scattering factors (Mizoguchi et al., 1978 Kudo et al., 1978). In the amorphous substitution method several alloys A, are used, where x is fixed and B or A is replaced by a component of similar size and chemical affinity but different scattering factor (Chipman et al., 1978 Williams, 1982). In these methods it is tacitly assumed that the atomic distribution functions in the alloy series are the same or, at least, do not differ much. 

A third, less obvious limitation of sampling methods is that, due to the heavy computational burden involved, simpler interatomic potential models are more prevalent in Monte Carlo and molecular dynamics simulations. For example, polarizability may be an important factor in some polymer crystals. Nevertheless, a model such as the shell model is difficult and time-consuming to implement in Monte Carlo or molecular dynamics simulations and is rarely used. United atom models are quite popular in simulations of amorphous phases due to the reduction in computational requirements for a simulation of a given size. However, united atom models must be used with caution in crystal phase simulations, as the neglect of structural detail in the model may be sufficient to alter completely the symmetry of the crystal phase itself. United atom polyethylene, for example, exhibits a hexagonal unit cell over all temperatures, rather than the experimentally observed orthorhombic unit cell [58,63] such a change of structure could be reflected in the dynamical properties as well. 

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