“…It is noteworthy that the bulk conductivity of the sintered (CeO 2 ) 0.5 (BiO 1.5 ) 0.5 is the only contribution which is clearly measurable in the present work. This is because the grain boundary effects involve complex contributions, such as those from the interphases due to the strong reaction between the metallic electrodes and bismuth-containing electrolytes. , Our XRD did not reveal any evidence of the presence of interphases on the sample surface after the conduction measurements, probably owing to a content below the experimentally detectable limit. 7 Comparison of the impedance spectra measured at 300 °C for the sintered solid solution (CeO 2 ) 0.50 (BiO 1.5 ) 0.50 using different electrodes. 8 The temperature dependence of (a) the bulk and (b) grain boundary conductivities of the sintered solid solution (CeO 2 ) 0.50 (BiO 1.5 ) 0.50 using a silver electrode.…”
A series of nanocrystalline solid solutions (CeO2)1
-
x
(BiO1.5)
x
(x = 0.0−0.5) were synthesized
by mild hydrothermal conditions at 240 °C. The products were characterized by X-ray
diffraction (XRD), scanning electronic microscope (SEM), X-ray photoelectron spectroscopy
(XPS), and electron paramagnetic resonance (EPR). Different from the solid-state reaction
systems, the solution limit of Bi2O3 in ceria by hydrothermal conditions was as high as ca.
50%. XRD data showed that all solid solutions crystallized in single-phase cubic fluorite-type structure. The average grain size of all solid solutions was within nanometer scale.
XPS data gave evidence of the presence of Bi(III) and Ce(IV) on the surface of the doped
ceria. EPR measurements confirmed Ce(III) ions in the bulk of the sintered solutions. When
the content of dopant Bi2O3 in ceria was lower than the limit, air firing of the as-made doped
ceria up to 800 °C did not lead to any structural transformation. For the solution (CeO2)0.5(BiO1.5)0.5, however, sintering it in air at 800 °C would destabilize the cubic fluorite structure
and result in segregation of an unknown phase. The ionic conduction measured by impedance
spectroscopy showed that the solid solutions with dopant content lower than the limit
exhibited primarily the bulk conduction, whereas for the sintered (CeO2)0.5(BiO1.5)0.5, both
the bulk and grain boundary resistance decreased dramatically with increasing temperature
when using silver electrode. The solution (CeO2)0.6(BiO1.5)0.4 was determined to be the best
conducting phase. For the nanocrystalline solutions (CeO2)1
-
x
(BiO1.5)
x
, the bulk conduction
was due to oxide ions. The variations of the activation energy and conductivity with dopant
content were interpreted in terms of the relative content of the dopant−defect complexes,
CeCe‘Vö/BiCe‘Vö
@mx@
.
“…It is noteworthy that the bulk conductivity of the sintered (CeO 2 ) 0.5 (BiO 1.5 ) 0.5 is the only contribution which is clearly measurable in the present work. This is because the grain boundary effects involve complex contributions, such as those from the interphases due to the strong reaction between the metallic electrodes and bismuth-containing electrolytes. , Our XRD did not reveal any evidence of the presence of interphases on the sample surface after the conduction measurements, probably owing to a content below the experimentally detectable limit. 7 Comparison of the impedance spectra measured at 300 °C for the sintered solid solution (CeO 2 ) 0.50 (BiO 1.5 ) 0.50 using different electrodes. 8 The temperature dependence of (a) the bulk and (b) grain boundary conductivities of the sintered solid solution (CeO 2 ) 0.50 (BiO 1.5 ) 0.50 using a silver electrode.…”
A series of nanocrystalline solid solutions (CeO2)1
-
x
(BiO1.5)
x
(x = 0.0−0.5) were synthesized
by mild hydrothermal conditions at 240 °C. The products were characterized by X-ray
diffraction (XRD), scanning electronic microscope (SEM), X-ray photoelectron spectroscopy
(XPS), and electron paramagnetic resonance (EPR). Different from the solid-state reaction
systems, the solution limit of Bi2O3 in ceria by hydrothermal conditions was as high as ca.
50%. XRD data showed that all solid solutions crystallized in single-phase cubic fluorite-type structure. The average grain size of all solid solutions was within nanometer scale.
XPS data gave evidence of the presence of Bi(III) and Ce(IV) on the surface of the doped
ceria. EPR measurements confirmed Ce(III) ions in the bulk of the sintered solutions. When
the content of dopant Bi2O3 in ceria was lower than the limit, air firing of the as-made doped
ceria up to 800 °C did not lead to any structural transformation. For the solution (CeO2)0.5(BiO1.5)0.5, however, sintering it in air at 800 °C would destabilize the cubic fluorite structure
and result in segregation of an unknown phase. The ionic conduction measured by impedance
spectroscopy showed that the solid solutions with dopant content lower than the limit
exhibited primarily the bulk conduction, whereas for the sintered (CeO2)0.5(BiO1.5)0.5, both
the bulk and grain boundary resistance decreased dramatically with increasing temperature
when using silver electrode. The solution (CeO2)0.6(BiO1.5)0.4 was determined to be the best
conducting phase. For the nanocrystalline solutions (CeO2)1
-
x
(BiO1.5)
x
, the bulk conduction
was due to oxide ions. The variations of the activation energy and conductivity with dopant
content were interpreted in terms of the relative content of the dopant−defect complexes,
CeCe‘Vö/BiCe‘Vö
@mx@
.
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