Temperature dependence of Bi₂O₃ structural parameters close to the α–δ phase transition

Abstract

This article presents the results of in situ X-ray powder diffraction, Raman spectroscopy, and electrical impedance spectroscopy of the α-phase of Bi₂O₃, at 0.1 MPa in the temperature range below and above the α–δ-phase transition. This work demonstrated subtle nonlinear temperature variations of the cell parameters, of the hard-mode Raman shift, and of the activation energy of electrical conductivity in the temperature range about 100–120°C below the α–δ phase transition temperature T _Tr ≈ 725°C in Bi₂O₃. At T < 600°C, the linear variation of the inverse dielectric susceptibility (χ ⁻¹) correlates well with the hard mode frequency shift Δ(ω ²) of Raman A_1g mode as Δ(χ ⁻¹)/Δ(ω ²) ≈ 5.5 × 10⁻⁷ cm². A structural model describing the mechanism of O²⁻ anion distribution and electric dipole disordering in the vicinity of T _Tr is discussed.

Keywords:

• Bi₂O₃
• anionic conductor
• Raman shift
• phase transition
• cell parameters

Acknowledgements

F. Schröder and N. Bagdassarov are grateful to DAAD for financing the cooperation project with Linköping University, Sweden. F. Schröder thanks Prof. W. Aßmus, Institute of Physics, Crystal Physics Lab, University of Frankfurt, Dr L. Fink and T. Bernert, Institute of Analytical Chemistry, X-Ray Lab, University of Frankfurt, for their support of the experimental work.