Local Mid-Range Order in La 2 O 3 –Nb 2 O 5 –B s O 3 and BaO–Nb 2 O 5 –P 2 O 5 Glasses According to Full X-Ray Scattering Data

Curves of full x-ray scattering at wavelength 0.20735 Å were measured and the corresponding radial distribution functions (RDFs) of the electron density for glasses in the systems La 2 O 3 –Nb 2 O 5 –B 2 O 3 and BaO–Nb 2 O 5 –P 2 O 5 were separated out. Peaks indicating the presence of a pronounced medium-range order in the glasses under study are clearly observed in the RDF at distances up to about 1 nm. Consideration of the RDF shows that for the BaO–Nb 2 O 5 –P 2 O 5 glasses with high BaO content, the medium-range order manifests in the form of chains of barium polyhedra that do not lie in the low-index planes of an ideal BaO crystal. For the La 2 O 3 –Nb 2 O 5 –B 2 O 3 glasses, chains of lanthanum polyhedra are observed, which are similar to polyhedra in the LaB 3 O 6 crystal linked via borate groups. In the considered glasses of both systems, niobium polyhedra do not form extended chains.