Effect of nanophase separation on crystallization process in Ge–Se glasses studied by Raman scattering

Abstract

We have found evidence of nanophase separation of the two structural units, Ge 2(Se 1/2) 6 ethane-like units and Ge(Se 1/2) 4-tetrahedra ones, in the Ge content range of 0.30–0.37 in Ge x Se 1− x glasses by investigating Raman spectra in a temperature range of 300–1000 K. The influence of nanophase separation over the crystallization processes induced by heating the bulk glasses beyond the glass-transition temperature, T g ’s , is explained in a medium-range-order structural point of view. A randomly distributed Ge 2(Se 1/2) 6 ethane-like unit induces an additional stress to the backbone. The local stressed structure relaxes through breaking the Ge–Ge bond (constituting the ethane-like unit) and acquiring a nearby Se atom (belonging to the Se–Se wrong bonds) to construct the corner-shared Ge(Se 1/2) 4-tetrahedra units. An increased nanophase separation promotes the nucleation of GeSe crystal in the super-cooled liquid state of Ge x Se 1− x ( x=0.36 and 0.37) in which we obtained the crystalline GeSe 2 and GeSe simultaneously, since a considerable population of ethane-like units lets them cluster in the glasses.