The optical band gap (${\mathit{E}}_0$) and thermal diffusivity (α) of bulk ${\mathrm{Ge}}_{\mathit{x}}$${\mathrm{Sb}}_5$${\mathrm{Se}}_{95\mathrm{-}\mathit{x}}$ and ${\mathrm{Ge}}_{\mathit{x}}$${\mathrm{Sb}}_{10}$${\mathrm{Se}}_{90\mathrm{-}\mathit{x}}$ glasses have been measured using the photoacoustic technique. The behavior of ${\mathit{E}}_0$ and α as the mean coordination number 〈r〉 is varied shows a maximum at 〈r〉=2.6. The anomalous behavior at 〈r〉=2.6 is explained on the basis of changes in the network topology due to the formation and development of layered structure in these glasses.

• Received 10 June 1991

DOI:https://doi.org/10.1103/PhysRevB.45.8112