MIDDLE RANGE ORDER IN GLASSES OF La2O3–Nb2O5–B2O3 AND BaO–Nb2O5–P2O5 SYSTEMS ACCORDING TO X-RAY TOTAL SCATTERING

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We have obtained the X-ray total scattering patterns at wavelength 0.20735 ? and corresponding to them radial distribution functions (RDF) of electron density for glasses in the La2O3–Nb2O5–B2O3 and BaO–Nb2O5–P2O5 systems. The RDF demonstrate separate peaks at distances below ~1 nm which points on the middle range ordering in the considered glasses. The consideration of RDF for BaO–Nb2O5–P2O5 glasses system with high concentration of BaO show that the middle range order is caused by the polyhedra chains of ideal BaO crystal, and these chains does not belong to any low-index crystal plane. For La2O3–Nb2O5–B2O3 glasses system the polyhedra chains are observed which resemble those in the LaB3O6 crystal, with polyhedra bound through borate groups. For all considered glasses the niobium polyhedra does not form extended chains.