  How atoms in covalent solids rearrange over a medium-range length-scale
during amorphization is a long pursued question whose answer could profoundly
shape our understanding on amorphous (a-) networks. Based on ab-intio
calculations and reverse Monte Carlo simulations of experiments, we
surprisingly find that even though the severe chemical disorder in a-GeTe
undermined the prevailing medium range order (MRO) picture, it is responsible
for the experimentally observed MRO. That this thing could happen depends on a
novel atomic packing scheme. And this scheme results in a kind of homopolar
bond chain-like polyhedral clusters. Within this scheme, the formation of
homopolar bonds can be well explained by an electron-counting model and further
validated by quantitative bond energy analysis based. Our study suggests that
the underlying physics for chemical disorder in a-GeTe is intrinsic and
universal to all severely chemically disordered covalent glasses.
