Phase transitions and electrical properties of Bi 2O 3 up to 2.5 GPa

Abstract

The effect of pressure between 0.5 and 2.5 GPa on the phase transitions and electrical conductivity of Bi 2O 3 has been studied by the use of electrical impedance spectroscopy. By analyzing the Arrhenius plots gained from the electrical conductivity measurements in the temperature range of the α – δ phase transition, the pressure dependence of the critical temperature ( T c ) and activation energy were determined. The measurements demonstrated that the pressure effect between 0.5 and 2.5 GPa has a significant effect on the α – δ phase transition temperature in Bi 2O 3, and the increase of T c for the α – δ phase transformation is more than 60 ∘C compared to previous research with DTA [E.M. Levin, R.S. Roth, Polymorphism of Bismuth Sesquioxide. I. Pure Bi 2O 3, Journal of Research of the National Bureau of Standards–A. Physics and Chemistry 68A (2) (1964) 189–195]. The activation energies of electric conductivity in α – δ phases seem not to be affected by raising the pressure. During cooling, the δ – α transformation occurred approximately at the temperature corresponding to T c monitored during the heating cycle. Neither a δ – β , a δ – γ phase transformation nor a hysteresis effect has been found under pressure, which is in contrast with normal pressure studies that used DTA, electrical conductivity measurements and XRD [E.M. Levin, R.S. Roth, Polymorphism of Bismuth Sesquioxide. I. Pure Bi 2O 3, Journal of Research of the National Bureau of Standards–A. Physics and Chemistry 68A (2) (1964) 189–195; H.A. Harwig, A.G. Gerards, Electrical Properties of the α -, β -, γ - and δ -Phases of Bismuth Sesquioxide, Journal of Solid State Chemistry 26 (1978) 265–274].