Anomalies of physical properties in alpha-Bi2O3 - A phase transition governed by the electronic mechanism?

A number of physical properties of alpha-Bi2O3 was studied: the thermal expansion, thermally stimulated conductivity, electrical resistivity, and dielectric permeability. X-ray diffraction, DTA, and differential scanning calorimetry measurements were also carried out. Several anomalies were observed: a small maximum and drastic rise of the single crystal dielectric permeability, a sharp drop of the electric resistivity, a jump and change in sign Of the thermally stimulated current, and an exothermal maximum an differential heat capacity. At the same time, the monoclinic lattice symmetry of alpha-Bi2O3 was retained over the temperature range where these anomalies were found.