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Struktur und Dynamik Poster: Mi., 14:00–16:30 M-P136
X-ray diffraction, neutron diffraction and EXAFS study of amorphous Ge15Te85
I. Kaban 1 , P. Jóvári 2 , W. Hoyer 1 , E. Welter 3
1 Institute of Physics, Chemnitz University of Technology, D-09107 Chemnitz, Germany
– 2 Research Institute for Solid State Physics and Optics, H-1525 Budapest, POB
49, Hungary – 3 Hamburger Synchrotronstrahlungslabor HASYLAB am Deutschen
Elektronen-Synchrotron DESY, Notkestrasse 85, D-22603 Hamburg, Germany
The atomic structure of amorphous Ge15Te85 has been studied by X-ray and neutron
diffraction and X-ray absorption spectroscopy at the Ge K-edge.
Neutron diffraction experiments were carried out with the liquid and amorphous materials
diffractometer SLAD at NFL, Studsvik. The incident wavelength of neutrons
was 1.11 ˚A. The scattered intensity was measured between 0.4 ˚A −1 and 10.4 ˚A −1 .
X-ray diffraction experiments were carried out at the BW5 experimental station at
HASYLAB, Hamburg. The energy of the radiation was 125 keV (0.101 ˚A). Scattered
intensities were measured between 0.5 ˚A −1 and 20 ˚A −1 .
EXAFS measurements at the Ge K-edge (11103 eV) were carried out at the beam line
A1 of HASYLAB in transmission mode using a Si (111) double-crystal monochromator.
The ionization chambers were filled with N2-Ar mixture. The pressure inside the
sample chamber was of the order of 10 −2 mbar.
The diffraction measurements were modelled simultaneously with EXAFS data by
the reverse Monte Carlo (RMC) simulation technique. Combination of the three independent
measurements allowed separation of the partial pair correlation functions
gGeT e(r) and gT eT e(r) and estimation of the corresponding coordination numbers.
The mean Ge-Te and Te-Te distance obtained in the present study are rGeT e = 2.60 ˚A
and rT eT e = 2.79 ˚A, and the coordination numbers: NT eT e = 1.64 and NGeT e = 3.53. It
is assumed that the structure of amorphous Ge15Te85 consists of GeTe3/2 and GeTe4/2
units bridged through the net of Te atoms.