Amorphous structure in Te-X-I (X:S, Se) mixtures

X-ray diffraction and Raman scattering measurements have been carried out on amorphous-(Te3I2)I1-xSx and (Te1/2I1/2)(1-y)Se-y mixtures. The results are summarized as follows. (1) S atoms in the amorphous Te-S-I mixture do not combine with Te and I atoms but form twofold sulfur clusters, whereas Se atoms in the amorphous Te-Se-I mixture are covalently bonded to Te atoms, and form -Se-Te- linkages. (2) 1 atoms are preferentially bonded to Te atoms in both amorphous mixtures. (3) The coordination number of constituent atoms in the mixture is determined to be two for S, Se and Te, and one for I, by a least-squares fit to the observed intensity function. (4) The structural feature in the sulfide mixture is substantially unchanged in both amorphous and liquid states, except for an increase in the coordination number around a central Te atom.