Bismuth coordinance in dilute alloys of the noncrystalline Se100−xBix system

The glass transition temperature, T_g, and the coordination peak of the radial distribution function, obtained from electron diffraction experiments, are studied for amorphous thin films of the Se_100−xBi_x system (x ≤ 8) prepared by vacuum evaporation. The controversial problem of the coordination of Bi in these alloys is raised. The T_g data versus composition are analyzed by means of a simple analytic model. All results can be interpreted by assuming that the average coordination of Bi for the more dilute portions of the system is four, as opposed to the expected value of three, and three when x is greater than 5.