Speaker
Mr
Masilo Ramafemo
(University of Witwatersrand)
Description
Bismuth-oxide based electrolytes are well known for their high oxide ion conductivity at intermediate temperatures (300-700°C). Indeed, the defect fluorite structured δ-phase of Bi2O3 shows the highest known oxide ion conductivity of any material. Unfortunately, this phase is only stable above 730°C and much research has been carried out on stabilizing this phase to lower temperatures through solid solution formation with other oxides. The aim is to work towards a better understanding of these materials in terms of structure and ion conductivity so that better SOFC electrolytes can be designed to run at lower temperatures (between 300 – 600°C). These materials will thus be studied at elevated temperature ranges. The longer-term stability of promising materials will also be investigated to determine how thermal cycling degrades the material and affects the conductivity.
The effects of Y3+ and Pb2+ double substitutions in Bi2O3 has been examined in the Bi2O3-PbO-Y2O3 system using X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), and VT-Raman spectroscopy. All these characterization techniques show that samples having Y3+ as a major substituent have a single (δ-phase) phase structure. Pb2+ is isoelectronic with Bi3+, thus the aim of including Pb2+ is to eventually try and gain insight into the effects of the lone pair of electrons in the mobility of the oxide ions through the lattice.
Primary author
Mr
Masilo Ramafemo
(University of Witwatersrand)
