Formation of Paramagnetic Defects in Oxide Glasses During the Bombardment of Their Surface with Charged Particles

Abstract

ABSTRACTHeavy-ion bombardment of a glass surface is a conventional laboratory technique for producing damage of interest for radioactive waste encapsulation. At energy of order 100 keV such a bombardment simulates the damage produced by α-recoil nuclei and fission fragments resulting from the nuclear decay. The damage region is 100–500 nm depending on conditions of the bombardment.In the present work some results of EPR study of point defects formed in silicate, borate, borosilicate, phosphate and other oxide glasses irradiated with different charge particles (C, N, O, Ar. Mn, Cu, Pb) at energy E=150 keV and large total fluence of ions (up to 1017 cm-2) are reported. Electron paramagnetic resonance (EPR) is a very sensitive technique which gives an information on the structure of point defects and their content. It is shown that in some cases (for example, in borate glasses) the oxygen hole centers similar to ones observed in γ-irradiated glasses are formed after ion bombardment. However, in the majority of cases new defects which are not typical of γ-irradiated oxide glasses were found They were large molecular oxygen ions (O2-O3-O4-) located in the cavities formed under ion bombardment in the near surface layer of glass. It should be noted that the relative content of these defects is of the order of several tens per 1000 incident ions. This content decreases with increasing fluence and atomic mass of incident ions. It indicates indirectly that point defects are clustered when the damage of the near surface layer becomes strong. The formation of gaseous oxygen is possible in cavities of the damage surface layer.It was found that some elements (for example C, N and transition metals) form chemical compounds with oxygen. The migration of alkali ions promotes the formation of such compounds since the chemical compounds were detected by means EPR in glasses rich in alkali oxides.