In this paper the results of X-ray diffraction experiments of
Ln-Si-Al-O-N (Ln = La, Gd, Yb) glasses are presented. Total structure
factors and pair correlation functions allow the determination of the
first coordination sphere of Ln atoms. The bond lengths observed
correspond to the ionic radii of the Ln-ions surrounded by oxygen and
nitrogen atoms. The presence of non-bridging nitrogen is discussed
together with results of neutron diffraction, NMR-experiments and
XPS-studies of other authors.