NSLS-II Seminar

The accurate determination of the structure of amorphous materials is far from routine with intense debate over irreconcilable discrepancies between the interpretation of X-ray and neutron diffraction results and theoretical calculations. There even exists a lack of consensus within the literature concerning the origin of the first strong diffraction peak (FSDP) which exists for most amorphous and liquid materials. Here we present a computational determination of the average atomic structure of amorphous red phosphorus (a-rP) from 0 to 6.3 GPa. These computations were constrained by pair correlation functions determined from high-quality x-ray diffraction data. We will show that the average structure of a-rP consists of P3 triangles, and P4 pyramids linked by chains of P atoms. We will also demonstrate a direct and positive correlation between the a-rP FSDP scattering intensity and the fraction of atomic scale void-space. Additionally the pressure dependence of the FSDP position will be shown to be directly attributable to the nominal void spacing and void periodicity. The result of the analysis of additional disordered materials, ranging from weak to strong liquids and glasses, will be shown to reproduce the same positive correlations.