THE RELATION BETWEEN THE MELT TOPOLOGY AND GLASS-FORMING ABILITY FOR LIQUID GE-SE ALLOYS

The topology of liquid GeySe1-y (0 less-than-or-equal-to y less-than-o r-equal-to 1) alloys, at the compositions y = 0.33, 0.4, 0.5 and 1, is studied using neutron diffraction to measure the Bhatia-Thornton numb er-number partial structure factor S(NN)(Kr1) where k and r1 are, resp ectively, the scattering vector and nearest-neighbour distance in real space. SNN(kr1) has, for the range 0 less-than-or-equal-to kr1 less-t han-equal-to 10, a prominent three-peak character in the case of the g lass-forming melt GeSe2 (y = 0.33). This character changes significant ly with increasing y: the so-called first sharp diffraction peak (FSDP ) is virtually eliminated at y = 0.5, a composition for which the amor phous state is not formed by usual bulk-quenching methods, and the thi rd peak becomes a shoulder to the second at y = 1, The concomitant cha nges on both the short and intermediate real-space length scales are d iscussed in terms of a break-up of the GeSe2 network structure. It is found that liquid GeSe is not characterized by a regular octahedral co ordination environment but that it is topologically similar to liquid As.