Change in the topology of the glass forming liquid GeSe2 with increasing temperature

The change in topology with increasing temperature of liquid GeSe2 was stud ied by using neutron diffraction to measure the Bhatia-Thornton number-numb er partial structure factor, S-NN(Q), where Q is the scattering vector. As the temperature is raised from 800 to 1100 degrees C there is a broadening but little other change in the peaks describing the local coordination envi ronment. There is, however, a collapse of the intermediate range atomic ord ering of the network associated with the Ge-Ge correlations as manifest by a substantial reduction in the height of the first sharp diffraction peak a nd a shift in its position from 0.99(1) to 1.05(1) Angstrom(-1). The change s in the structure with increasing temperature mimic those observed as the composition of liquid GeSe2 is changed to the GeSe stoichiometry by the add ition of germanium. The significance of the results for recent Car-Parinell o type ab-initio molecular dynamics simulations is briefly discussed.