Crystalline-amorphous transitions of Ge-Se alloys by mechanical grinding

X-ray diffraction and differential scanning calorimetry (DSC) measurements of Se and GeSe2 during ball milling have been investigated. In this study, amorphous Se and GeSe2 are synthesized by mechanical grinding (MG) recognized as a method of inducing a crystalline-amorphous phase transition. The amorphization of Se is caused from distortion between helical chains connected by van der Waals forces. The enthalpy AH for crystallization of Se by rapid quench is lower than that by the MG. This result suggests that the difference of AH corresponds to that of the structures in intermediate range. Monoclinic GeSe2 is amorphized by disordering between the connected tetrahedra. It is considered that the tetrahedral unit of GeSe2 by the MG is distorted with wide distributions. GeSe2 is completely amorphized after 4 h of grinding, and Se after 30 h in the present milling. The difference indicates that disordering between the connected tetrahedral units in monoclinic GeSe2 is induced more easily than that between chains in trigonal Se. (C) 2001 Elsevier Science B.V. All rights reserved.