Neutron diffraction study of liquid As-Se and As-Te systems

The neutron diffraction measurement in liquid As_xSe_1-x and As_xTe_1-x alloys with x=0.20∼0.571 has been carried out to analyze the local atomic arrangement in these liquid alloys. The first sharp diffraction peak (FSDP) of the structure factor, S(Q), in the liquid As-Se alloys was observed at all x, indicating that existing structural units are partially connected as in the amorphous state, while, the FSDP in the liquid As-Te alloys almost disappears, particularly, in the Te rich composition range. The first peak of atomic pair distribution function, g(r), in the liquid As-Se alloys is well-resolved, reflecting the strong As-Se covalent bondings. On the other hand, the first peak of g(r) in the liquid As-Te alloys is broadened and its position largely shifts with x. Results by the least square analysis for diffraction intensities have been summarized as follows: The connecting AsSe_3/2 pyramidal unit, which is the basic structural element at As₂Se₃, is formed over a wide composition range in the As-Se alloys but bondings between like atoms such as Se-Se and As-As are present only in the limited composition range. On the other hand, in the liquid As-Te alloys both As-As and Te-Te bondings, in addition to the As-Te one, can be observed at all x containing As₂Te₃. The results have also pointed out that the metallic property of the liquid As-Te alloys is attributable to the change of the bonding nature relating to Te on melting.