Local- and intermediate-range atomic order in Ga₂Ge₃Se₉ glass. Complementary use of X-rays and neutrons

Local- and intermediate-range atomic order in a (Ga₂Se₃)_0.25(GeSe₂)_0.75, or Ga₂Ge₃Se₉ glass, having a high infrared transparence coefficient, was investigated by using a combination of anomalous X-ray scattering (AXS), X-ray and neutron diffraction (XRD and ND), and reverse Monte Carlo (RMC) modeling. By adding the ND pair distribution function to AXS and XRD results, reasonable partial structure factors and partial pair distribution functions were obtained, even applying no constraints of shortest interatomic distances during the RMC calculation procedure. Total coordination numbers around Ga, Ge, and Se atoms are 3.80, 4.68, and 2.25, respectively, which contradict the 8 − N rule. The numbers of Ga-Ga, Ga-Ge, Ge-Ga, and Ge-Ge wrong bonds were found to be 0.71, 1.32, 0.76, and 1.12, respectively. In the three-dimensional atomic configuration, the structure looks inhomogeneous in both density and concentration. (author)