Isotope effects on the glass transition phenomena and thermal properties of B2O3 glass

Boron isotope effects on the glass transition phenomena and low-temperature heat capacity of B ₂O ₃ glass with various ¹⁰B to ¹¹ B ratios were examined. The apparent activation enthalpy (H*) of the glass transition shows a large isotope mixing effect. H* of the glass with ¹⁰B: ¹¹B = 0.5:0.5 is 451 kJ/mol, while that of ¹⁰B-glass is 404 kJ/mol and that of ¹¹B-glass is 348 kJ/mol. This is attributed to the fact that the glass transition is a cooperative phenomenon; mixing the isotopes should diminish the cooperative behavior. The isotope effect below the glass transition region is small. The low temperature heat capacity, from 160 to 300 K, of the glass with ¹⁰B: ¹¹B = 0.5:0.5 is slightly (<6%) larger than that of pure ¹⁰B-and pure ¹¹B-glasses.