Temperature Dependence Of Short-range Order Research Articles

Sensitivity of liquid-state inherent structure to details of intermolecular forces

Temperature dependence of short-range order has been systematically studied in two model atomic liquids, using molecular dynamics computer simulation linked to steepest-descent mapping of configurations onto potential minima. Owing primarily to differing attractive forces, the natural crystal structures differ for the two models (face-centered-cubic vs primitive hexagonal). Only one of these crystals is geometrically consistent with the number of particles (256) and boundary conditions (periodic, cubic cell) used for both. Nevertheless, both liquids were found to exhibit temperature dependence of short-range order arising solely from vibrational smearing of underlying temperature-independent inherent structure. The latter differs substantially for the two models, and in each case resembles a highly defective version of the corresponding crystal.

Interactions, local order, and atomic-rearrangement kinetics in amorphous nickel-phosphorous alloys.

Molecular-dynamics computer simulations have been carried out to study the liquid and amorphous solid states for a system comprising 120 Ni and 30 P atoms. This study utilized additive central pair potentials to model the interactions. Emphasis has been placed on the geometry of the resulting potential-energy hypersurface for the system as a whole to explain temperature dependence of short-range order, and to characterize bistable degrees of freedom that dominate low-temperature properties in this, and other, amorphous solids. A small collection of transition states and associated reaction coordinates for such degrees of freedom has been numerically constructed. The corresponding atomic motions tend to be localized mainly on a small subset of the atoms, but are diverse insofar as which chemical species are involved, in barrier height and asymmetry, and in the nonlinearity of the collective reaction coordinate.

Concentration and temperature dependence of short-range order in Ni–Ta solid solutions using the X-ray diffraction method

Diffuse X-ray scattering investigations on the existence of short-range order (SRO) have been carried out in the Ni-Ta system for different concentrations and annealing temperatures. The values of the SRO parameters for the first coordination shell are observed to have anomalously large negative values for all the samples studied. These values of α1 depend upon the annealing temperatures and the concentration of Ta atoms in the Ni-Ta system. The results of the theoretical predictions of the ordering potential, obtained with the formulae of the electronic theory of SRO, confirm the existence of very strong attractive correlation between the atoms of the different species in this system.

An X-ray structural investigation of amorphous rubbers

The X-ray method was used in calculating the differential curves of radial distribution in investigations of short range order which were carried out for a number of amorphous rubbers (polybutadiene, butadiene-nitrile rubbers) and polyacrylonitrile. The effect of temperature and of side groups on the structure of the amorphous polymers was investigated. The temperature-dependence of short range order was investigated by analysing the ratios of the heights of intramolecular and intermolecular peaks proposed by the authors as additional parameters of the amorphous state. The validity of the latter parameters for describing changes taking place within the limits of the amorphous state is demonstrated, taking as examples polyethylene, polytrifluorochloroethylene and polybutadiene. In the investigations of polybutadiene, polyacrylonitrile and a number of butadiene-nitrile rubbers it was found that the incorporation of even 18% of nitrile groups as side substituents already leads to a marked increase in the distance between the molecules in the entire volume of the polymer.