A pressure of 55kbar was applied to three cobalt-containing glasses by the use of a high-pressure apparatus of the simple squeezer type at room temperature for 30min. Compositsons of the glasses are; 72.0SiO
2, 10.2CaO, 13.9Na
2O, 1.54K
2O, 1.33B
2O
3, 0.25mole% Sb
2O
3 with 2.0wt% CoO to 100g of glass, 25.0K
2O, 75.0mole% B
2O
3 with 2.0wt% CoO to 100g of glass and 10.0K
2O, 90.0mole% B
2O
3 with 5.0wt% CoO to 100g of glass. Light absorption spectrum in the visible range of the specimens before and after application of the pressure were determined with a microspectrophotometer. From the experimental results changes in ionic distance between the Co
2+ ion and its neighbouring O
2+ ions and also changes in numbers of the O
2- ions coordinated around the Co
2+ ions were calculated by the Ligand Field Theory. Changes in refractive index of the specimens before and after the compression were also measured to determine the residual shrinkage of the glasses in bulk.
The results obtained are summerized as follows:
1) The three absorption peaks characteristic for both the four- and six- fold coordinated Co
2- ions in all of the glass specimens were shifted toward the shorter wave length by the compression; the three peaks at 535, 597 and 633mμ for the silicate glass were shifted to 532, 595 and 630mμ, those at 530, 595 and 633mμ for the high-alkali borate glass to 500, 573 and 613mμ, those at 463, 503 and 555mμ for the low-alkali borate glass to 440, 480 and 530mμ, each respectively.
2) The local shrinkage of the glass structure in the neighbourhood of the Co
2+ ions calculated from the shift of the absorption peaks were 0.005 for the silicate glass, 0.073 for the high-alkali borate glass and 0.078 for the low-alkali borate glass, whereas the shrinkages of the glasses in bulk calculated from their changes in refractive index were 0.02-0.05, 0.03-0.07 and 0.03-0.06 for the silicate and the high- and low-alkali borate glasses, respectively.
3) Besides the shift of the absorption peaks, developement of the new peaks at 440, 480 and 525mμ, which are probably attributed to the change in coordination number of the Co
2+ ions from four to six, were observed for the high-alkali borate glass.
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