Atomic Radial Distribution in Amorphous Selenium by X-Ray and Neutron Diffraction

Abstract

The atomic radial distribution in amorphous selenium at room temperature was determined independently from x-ray and neutron-diffraction patterns. Correction techniques were applied to reduce spurious oscillations in the distribution. The two si(s) intensity functions are in good agreement, and both methods show peaks in the radial distribution at 2.33, 3.7, 4.6, 5.8, and 7.(3) Å. The intensity patterns show no appreciable damping out of intensity peaks even at the experimental limit of s=13. This behavior results from the presence of short and well-defined interatomic distances in amorphous selenium. The intensity function can largely be accounted for by considering only two interatomic distances between the first and second nearest neighbors along the c-axis chain structure of hexagonal crystalline selenium. Thus, the spiral chain structure persists in the amorphous state with nearly unchanged geometry out to second neighbors, but in random orientations.