Effect of B2O3 concentration on the local atomic structure of lanthanum in lanthanum-borate glasses: XANES study and the principle of crystal-chemical similarity of the short-range order in glasses and crystals

Dependence of lanthanum local atomic structure in borate glasses La ₂O ₃-Nb ₂O ₅-B ₂O ₃ upon component composition was studied combining XANES, computer simulations using crystal chemical similarity (CCS) of a short-range order in glass and crystal, and multidimensional interpolation of spectra as the function of structural parameters. By this approach, the values of La-O bond lengths and angles in chains O-La-O were determined. Comparison of the obtained radial and angle distribution functions of oxygen atoms around La in the studied glasses with the same functions of the reference crystals revealed that within the existing CCS of La local structure in glasses and in B ₃LaO ₆, there is a decrease in the average length of La-O bonds by ∼ 0.1 Å and decrease of FWHF by ∼ 0.2 Å in the radial distribution of nearest O atoms, under retaining angle distribution of these atoms. It was shown that the ratio of intensities of the first two peaks in experimental La L₃ -edge XANES is an effective fingerprint of the number of nearest oxygen neighbors of lanthanum. Using the dependence of this ratio upon the component composition of glasses, the changes in the local structure of La under decreasing of B ₂O ₃ fraction from 72.5 to 47.5% were determined.