X-ray diffraction study of Na+ ions coordination in sodium borate glasses

X-ray diffraction measurements were performed on glasses of the type Na2O–B2O3 and Li2O–B2O3, in which the maximum content of Me2O is 0.3 mol per 1 mol of B2O3. By subtracting the radial distribution functions of the Li2O–B2O3 samples from those of Na2O–B2O3 glasses having the same molar ratios, difference curves were obtained in which peaks coming from the distribution of nearest neighbor atoms around Na+ ions were observed. The quantitative analysis showed that the environment of Na+ ions is not a regular polyhedron. About 5.0–5.5 O atoms surround Na+ ions; on the average 3.4–3.6 O atoms are 2.40–2.44 Å distant from Na+ ions while 1.5–2.0 other O atoms are at a distance of 2.75–2.80 Å.