Structural origin of broken chemical order in a GeSe2glass

Two clearly defined and chemically inequivalent Sn sites in the alloy glass (${\mathrm{Ge}}_{0.99}$ ${\mathrm{Sn}}_{0.01}$)${\mathrm{Se}}_2$ are observed using Mössbauer spectroscopy. These sites are identified with Sn impurity atoms replacing Ge in tetrahedral ${\mathrm{G}\mathrm{e}\left({\mathrm{Se}}_{1/2}\right)}_4$ units and ethanelike ${{\mathrm{Ge}}_2\left({\mathrm{Se}}_{1/2}\right)}_6$ units, and provide direct evidence for intrinsically broken Ge chemical order. Compositional variation of site intensities shows that the origin of this broken order derives from the existence of characteristic clusters in the network.