THE LOCAL ATOMIC ARRANGEMENT IN THE AMORPHOUS AS-TE-I SYSTEM

Raman spectroscopic, X-ray diffraction and extended X-ray absorption f ine structure measurements have been carried out on the amorphous (As0 .5Te0.5)(1-x)I-x, system with 0 less than or equal to x less than or e qual to 0.3. AsI3 molecular units and mixed-anion structural units are not formed in the system. The I atoms incorporated into amorphous As0 .5Te0.5 are preferentially bonded to Te atoms and terminate the As-Te network structure. The bond distances for all atomic pairs contained i n the first coordination shell remain almost constant for all composit ions studied. being r(As-As) = 0.252 +/- 0.001, r(As-Te) = 0.265 +/- 0 .002 and r(Te-I) = 0.274 +/- 0.002 nm, These numbers agree well with t hose determined by curve fitting the EXAFS oscillation functions. The total coordination numbers of As, Te and I atoms in the system are det ermined to be three, two and unity, respectively. (C) 1998 Published b y Elsevier Science B.V. All rights reserved.