Two-State Model for the Free Volume of Vitreous B2O3

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.