Infrared absorption spectra of gamma irradiated glasses of the system Li20-B2o3-Al2o3

ABSTRACT

Spectroscopic studies on alkali metal borate glasses have revealed that the structure of alkali metal borate glasses is dependent not only upon the content of the alkali metal ion but also upon the difference in the alkali metal ion [1] Basic characteristics of borate glass structures are generally agreed upon. The fundamental building block in vitreous B[2]O[3]- is the BO[3] groups either as a random network of boroxol rings beside some fraction of BO[3] triangles [2] connected by B-O-B linkages [bridging atoms][2] The boroxol group is composed of three corner-sharing BO[3] triangles which form a very highly planar ring. Recent studies concluded that any model which attempts to give a full description of the structure of B[2]O[3] must include a high concentration of boroxol group. The addition of alkali oxides modifies the boroxol rings; complex borate groups with one or two four-coordinated boron atoms are formed[4]. Alkali oxide is usually incorporated into B[2]O[3] glass ionically. The initial effect upon the introduction of alkali oxide into B[2]O[3] is the conversion of Sp [2] planar BO[3] units into more stable Sp3 tetrahedral BO[4]. units thereby preserving the B-O bonding without the creation of non bridging oxygen [NBO] ions. Early NMR studies [5] indicated that the conversion of 3-to-4 coordinated boron extends for levels of alkali oxide up to about 30 mol percent and that the NBO ions should be created in large numbers at alkali oxide concentrations above the 30 mol percent level The alkali borate glasses will be composed of structural groupings [boroxol, tetraborate, diborate, metaborate, pyroborate, and orthoborate] present in the various crystal structures of the alkali borate compounds. The abundance and type of structural units present depend upon the amount of alkali oxide incorporated into the glass. Detailed recent investigations of the infrared spectra of borate glasses and their corresponding crystalline derivatives have been carried by Kamitsos et al[6]'. The interpretation of the results is believed to be tough task, due to the complexity originating from the glassy nature of the materials and to the large number of possible structural groups found in borate glasses. In a previous investigation [7] the effect of progressive increasing gamma rays dose on the infrared spectra of ternary borosilicate glasses of the system BaO-B[2]O[3]-SiO[2] was studied Experimental results indicate that the intensities of the characteristic absorption bands generally decrease with radiation, the frequencies of all the observed bands remain unchanged, and new bands are formed. In this paper, the work is continued to make a vibrational analysis by comparing the spectra obtained before and after gamma-ray irradiation to search for a further support to the previous published work and emphasizing to the role of changing glass composition on the infrared spectra of the. ternary Li[2]O-B[2]O[3]-Al[2]O[3] glasses