Abstract
Transmission electron microscopy and related analytical techniques have been widely used to study the microstructure of different materials. However, few research works have been performed in the field of glasses, possibly due to the electron-beam irradiation damage. In this paper, we have developed a method based on electron energy loss spectroscopy (EELS) data acquisition and analyses, which enables determination of the boron speciation in a series of ternary alkali borosilicate glasses with constant molar ratios. A script for the fast acquisition of EELS has been designed, from which the fraction of BO4 tetrahedra can be obtained by fitting the experimental data with linear combinations of the reference spectra. The BO4 fractions (N4) obtained by EELS are consistent with those from 11B MAS NMR spectra, suggesting that EELS can be an alternative and convenient way to determine the N4 fraction in glasses. In addition, the boron speciation of a CeO2 doped potassium borosilicate glass has been analyzed by using the time-resolved EELS spectra. The results clearly demonstrate that the BO4 to BO3 transformation induced by the electron beam irradiation can be efficiently suppressed by doping CeO2 to the borosilicate glasses.
Highlights
Irradiation effect is almost inevitable in the transmission electron microscope (TEM) and the N4 data have been reported to be lower than those measured by nuclear magnetic resonance (NMR), due to the transformation of BO4 into BO3 units during the signal acquisition[11]
In alkali borosilicate (ABS) glasses, one of the irradiation effects is the transformation of tetrahedral BO4 into planar BO3 units as a result of the removal of alkali species out of the illuminated area, and the speed of this transformation decreases with the size of the alkali ions increase (Li+, Na+, K+ and Cs+)[11]
It should be noted that the energy resolution of both reference spectra were about 0.5 eV, better than that of our experimental spectra (1.2 eV), which means that the peak height/width of our experimental spectra (Fig. 1(b)) may not be directly compared with the superposition of the two fingerprint spectra
Summary
The latter gives the N4 of 60%, which is much lower than that for the KBS glass without CeO2 doping. Even though the error in the measurement of the Ce valence is estimated to be about ± (0.05 ~ 0.1), the peak-shift towards lower energy of the M4,5 edges indicates that there should be some Ce3+ions accompanying the major fraction of Ce4+ in the glass This result is consistent with a previous study which shows that Ce favors the valence state of + 4 when Ce is totally dissolved in the ABS glass matrix[19,21]. This work has presented an alternative approach for quantifying the boron speciation in glass materials
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