Degenerate Excited State in the Structure of B2O3

A degenerate excited state is essential to the description of structural rearrangements which account for the relaxational heat capacity, thermal expansion, and compressibility of vitreous B2O3. These relaxational responses cannot be simultaneously described by a two-state model, or by any model involving a single ordering parameter, as shown by the magnitude of the Prigogine—Defay ratio (π≠1). The apparent two-state behavior of the temperature derivatives, Δα and Δcp, and failure of a two-state model to predict a sufficiently large compressibility (pressure derivative), suggest an analysis of structural rearrangements in vitreous B2O3 in terms of a single ground state and a twofold degenerate excited state which is characterized by different volumes.