X-RAY-DIFFRACTION STUDY OF AMORPHOUS GE(SE1-XTEX)(2) ALLOYS

X-ray diffraction and Raman scattering measurements have been carried out on amorphous Ge(Se1-xTex)(2) alloys with x = 0 to 0.70. The first peak area of the distribution function indicates that the coordination number of Ge is nearly four at any of the compositions covered, sugge sting that tetrahedral units having Ge at the central site are formed in the system. Further, Raman vibrational modes corresponding to five anion-mixed GeX(4-n/2)Y-n/2 tetrahedral units were observed in this al loy. The Ge-Te bond length, 0.261 nm, in the anion-mixed tetrahedra, o btained by the least squares fit ting procedure for X-ray intensity fu nctions is closer to the sp(3)-orbital covalent distance, similar to t he Ge-Se bond length, which also evidences the existence of the tetrah edral units in the system.