Degenerate Excited State in the Structure of B2O3

Abstract

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 $\text{(π≠1)}$ . The apparent two‐state behavior of the temperature derivatives, Δα and Δc_p, 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.