Determination of Atomic-Scale Density of Materials from Total Scattering Profiles

Abstract

Atomic-scale density (microscopic density) for non-crystalline materials is sometimes hard to obtain when the sample contains microscopic grains and/or pores. This is also the case for crystalline materials that contain atomic scale defects. We propose a method for the determination of the microscopic density of an amorphous sample from total scattering data. Theoretically, the microscopic density can be calculated from the slope of the pair distribution function G(r) in the short-distance region from zero to the nearest neighbor. However, the observed G(r) in this region is greatly affected by unphysical modulation of the experimental scattering data and the derived structure factor S(Q). As a result, the estimated microscopic density has a large uncertainty. The proposed method removes the unphysical modulation of S(Q) and obtains a G(r) that satisfies theoretical conditions only using the coherent scattering intensity and the first neighbor distance. We have applied the present method to SiO2 glass, crystalline Ni powders, and a set of data from germinate glasses whose densities have been reported. The results of the present method are consistent with the reported values within ±5%.