The potential of XANES spectroscopy for studying the structure of boron-containing compounds is assessed by theoretical modelling of B K edge spectra of minerals. Spectra arising from three-fold coordinated boron sites differ considerably from spectra arising from four-fold coordinated sites. The characteristic shape of the spectra is governed first of all by short range order and, to a lesser extent, by medium range order. Areas of main spectral peaks depend only on the coordination of the photoabsorbing site and can thus be used for quantifying the portion of boron atoms in BO3 and in BO4 units, in minerals as well as in glasses. The width of the main peak of spectrum at a four-fold coordinated boron site generally increases with the the spread of the B-O distances but deviations from this correlation may be substantial. In contrast to spectra of minerals, XANES of BPO4 crystal is governed by long range order and is thus not a suitable model for studying XANES of borate glasses.
Connection between spectral features of BK edge XANES of minerals and the local structure
Rocca, Francesco
2006-01-01
Abstract
The potential of XANES spectroscopy for studying the structure of boron-containing compounds is assessed by theoretical modelling of B K edge spectra of minerals. Spectra arising from three-fold coordinated boron sites differ considerably from spectra arising from four-fold coordinated sites. The characteristic shape of the spectra is governed first of all by short range order and, to a lesser extent, by medium range order. Areas of main spectral peaks depend only on the coordination of the photoabsorbing site and can thus be used for quantifying the portion of boron atoms in BO3 and in BO4 units, in minerals as well as in glasses. The width of the main peak of spectrum at a four-fold coordinated boron site generally increases with the the spread of the B-O distances but deviations from this correlation may be substantial. In contrast to spectra of minerals, XANES of BPO4 crystal is governed by long range order and is thus not a suitable model for studying XANES of borate glasses.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
