Is the chemical threshold in certain chalcogenide glasses responsible for the threshold at the mean coordination number of approximately 2.7?

Assuming a strong tendency for chemical ordering, we defined a chemical thr eshold for T(0.4-x)P(x)Ch(0.6) glasses (T = Ge; P = As, Sb; Ch = S, Se). Fo r three types of bonding arrangement, including strong chemical ordering, w e calculated the formation energy dE per atom of the glasses under study. T he dependence of dE on the average coordination number [CN] indicates that the strongly chemically ordered state is probably the most stable. In this case, threshold-like behaviour is seen for [CN] = 2.7, where maximal values of -dE are reached. Hence, it is supposed that the threshold-like behaviou r in certain properties as a function of [CN] recently observed in some cha lcogenide glassy systems at [CN] approximate to 2.7 can be a consequence of the chemical threshold.