Physical properties of chalcogenide glasses in the ${\text{As}}_x{\text{Se}}_{1-x}$ system have been measured as a function of composition including the Young’s modulus $E$, shear modulus $G$, bulk modulus $K$, Poisson’s ratio $\nu$, the density $\rho$, and the glass transition $T_{\text{g}}$. All these properties exhibit a relatively sharp extremum at the average coordination number $⟨r⟩=2.4$. The structural origin of this trend is investigated by Raman spectroscopy and nuclear magnetic resonance. It is shown that the reticulation of the glass structure increases continuously until $x=0.4$ following the “chain crossing model” and then undergoes a transition toward a lower dimension pyramidal network containing an increasing number of molecular inclusions at $x>0.4$. Simple theoretical estimates of the network bonding energy confirm a mismatch between the values of mechanical properties measured experimentally and the values predicted from a continuously reticulated structure, therefore corroborating the formation of a lower dimension network at high As content. The evolution of a wide range of physical properties is consistent with this sharp structural transition and suggests that there is no intermediate phase in these glasses at room temperature.

• Received 14 October 2010

DOI:https://doi.org/10.1103/PhysRevB.82.195206