Publication date: 10th April 2024
Development of new fast ionic conductors requires a good understanding of factors critical for long-range ion transport. In this work, we focus on the Bi0.8Pr0.2O1.5 system, which is known to show very high oxide ion conductivity and high stability. At ca. 730 °C a β2 « β1 phase transition of order-disorder type occurs. Correlated with this phase transition are step-like changes in total conductivity (of 1 order of magnitude) and lattice volume [1]. In our previous work on this system [1], we concluded that with the increasing presence of oxide ions in the van der Waal gap, a significant change in the ionic conductivity mechanism occurs. At lower temperatures, oxygen migration occurs mainly via the oxygen atoms at the edge of the fluorite blocks (intra-planar conduction pathway); at higher temperatures, anions also migrate via sites in the van der Waals gap (inter-planar conduction pathway). The observed step change in total conductivity is mostly related to the presence of this additional conduction pathway.
In this work, we seek to determine the processes responsible for the β2 « β1 phase transition. A detailed study of the rhombohedral Bi0.8Pr0.2O1.5 system, including detailed analysis of the local structure using both reverse Monte Carlo (RMC) analysis of total neutron scattering data and ab intio DFT simulations. These results have been used to clarify details of the conduction mechanism, particularly the interplay between the electronic structure of bismuth (specifically its 6s² lone electron pair) and the redistribution of oxygen ions, thereby influencing ion transport dynamics.
This work has been supported by the National Science Centre, Poland grant number UMO-2018/31/B/ST5/03161