Breakdown of intermediate-range order in liquid GeSe2 at high temperatures

The structure of Liquid GeSe2 at T = 1373 K has been investigated by first-principles molecular dynamics. The calculated total neutron structure factor is in good agreement with recent experimental data. We found that the disappearance with increasing temperature of the first sharp diffraction peak (FSDP) in the total neutron structure factor is due to an increase of short-range chemical disorder. At T = 1373 K various bonding configurations coexist in close amounts, such as the Ge-GeSe3, Ge-GeSe2 and Se-SeGe2 motifs. This contrasts with the behaviour of liquid GeSe2 at T = 1050 K, for which more than half of the Ge atoms are four-fold coordinated to Se atoms in regular GeSe4 tetrahedra. Our result correlates the appearance of the FSPD in disordered AX(2) network-forming materials to the predominant presence of AX(4) subunits.