Oxygen permeation measurements were performed on two layered bismuth based oxide ceramics: a rhombohedral phase belonging to the Bi 2 O 3 -CaO system, (Bi 2 O 3 ) 0.73 -(CaO) 0.27 (BICAO) and a BICOVOX phase. Oxygen permeability for these systems was compared to permeability of the cubic fluorite type structure with composition (Bi 2 O 3 ) 0.75 (Er 2 O 3 ) 0.25 (BE25). Low oxygen permeability was observed for the pure ceramic.As for BE25, permeability was considerably increased if 40 vol% of silver was added to BICAO. In contrast, permeability was not improved by addition of gold to BICOVOX. For this latter phase, the oxygen molecular exchange at the surface is clearly the limiting step in the oxygen transfer.
The thermal behavior of the oxide ion-conducting solid
electrolyte
Bi4YbO7.5 was investigated using a combination
of variable temperature X-ray and neutron powder diffraction, thermal
analysis (DTA and TGA), and ac impedance spectroscopy. The title compound
shows a fluorite-type structure throughout the measured temperature
range (20–850 °C), with a phase separation at ca. 600
°C into a cubic δ-type phase and an orthorhombic phase
of assumed stoichiometry Bi17Yb7O36. This type of transition is a relatively common feature in bismuth
oxide-based systems and can limit their practical application. Here,
the transition was carefully studied using isothermal measurements,
which showed that it is accompanied by changes in oxide-ion stoichiometry,
as well as significant disorder in the oxide ion sublattice in the
δ-type phase. These results correlate with the observed electrical
behavior. Analysis of the total neutron scattering through reverse
Monte Carlo (RMC) modeling reveals details of the coordination environments
for both cations. The oxide-ion vacancy distribution seems to be consistent
with a favoring of ⟨100⟩ vacancy pairs, although ⟨110⟩
vacancy pairs exhibit the highest frequency as they have the maximum
likelihood. A vacancy ordering model based on three vacancies per
cell is presented.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.