Boron environments and irradiation stability of iron borophosphate glasses analysed by EELS

The coordination and stability under electron irradiation of boron in glasses with nominal molar composition 60P2O5 − (40 − x)Fe2O3 − xB2O3, for which x = 0, 5, 10, 15 and 20, have been investigated for the first time by electron energy loss spectroscopy (EELS) with transmission electron microscopy (TEM). Analyses confirm that boron is present in un-irradiated samples as tetrahedral BO4 units; there is no evidence of any trigonal BO3 units. TEM analysis reveals no tendency for sub-micron phase separation of the as-annealed glass. Iron borophosphate glasses exhibit high resistance to structural damage by electron beam irradiation by comparison with literature values for a range of other silicate and phosphate glasses. Large doses of highly intense irradiation result in the conversion of BO4 to BO3 units. The high irradiation resistance of these glasses could be related to the absence of mobile classical network modifiers such as alkalis and their associated non-bridging oxygens.

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