Electron beam induced structure changes in borosilicate and borophosphate glasses: a comparison by energy loss spectroscopy

Electron energy loss spectroscopy (EELS) applied to boron-containing glasses can provide 'fingerprint' spectra for boron coordination. Potassium borosilicate glass and iron borophosphate glass both containing 20 mol% of boron oxide were analysed in a 200 kV field emission gun transmission electron microscope (TEM). Results have been recorded for both glasses as a function of electron irradiation time. It is confirmed for the first time, that iron borophosphate glasses (unlike alkali borosilicate glasses) are stable in their BO4 tetrahedral configuration under typical TEM electron irradiation. This confirms in turn, that the depletion of alkali species (absent in the phosphate glasses studied) is the main reason for the irradiation induced change of boron coordination in the borosilicate glasses. In an attempt to separate knock-on damage from thermally activated (diffusion assisted) damage, we have commenced cooling stage experiments by observing time series of EELS spectra at a near liquid nitrogen temperature (96 K). Preliminary results indicate persistent, but slower, alteration of boron coordination in alkali-containing glasses.