SHORT-RANGE ORDER OF AMORPHOUS AND LIQUID AS-TE-I SYSTEM

Raman scattering and X-ray diffraction measurements have been carried out on the amorphous As50-xTe50Ix system with x = 0-25. The Raman band relating to the AsI3 molecular unit, which has been observed in both amorphous As-S-I and As-Se-I systems, was not detected in the present system. Raman spectra also revealed that mixed-anion structural units, such as As(Te-(3-n/2)I-n) type, are not present in the telluride syst em. It was made clear from the X-ray radial distribution analysis of t he system that the direct As-As bond is included in the first coordina tion shell, together with As-Te and/or Te-Te bonds, and that I atoms i ntroduced are preferentially coordinated to Te. The presence of the As -As bond was also confirmed by EXAFS measurement. Radial distribution functions in the liquid As40-xTe60Ix system(x = 0-35) obtained by neut ron diffraction showed that the liquid short-range order is similar to that in the amorphous state, except for an increase in the coordinati on number around Te.