Two-State Model for the Free Volume of Vitreous B2O3

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Abstract
New data on the density of B2O3 from 25° to 230°C are given. A two‐state equation of state for the volume is presented which fits the volume data from 350° to 1400°C. A specific structure for the two states is suggested and shown to be consistent with Raman data. Below 350°C and at high pressures the data indicated that the two‐state expressions for free volume still hold but the volume of the close‐packed structure becomes temperature and pressure dependent. The viscosity of B2O3 from the glass transition up to 1400°C and at high pressure is consistent with the equation of state and the hybrid equation of Macedo and Litovitz. The viscosity values above 1400°C indicate a breakup of the two‐state structures and the beginning of multistate behavior which results in a temperature‐dependent activation energy. The onset of this effect causes the ``apparent'' activation energy to increase above 1400°C.

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