Oxygen Transfer on Substituted ZrO2, Bi2O3, and CeO2 Electrolytes with Platinum Electrodes II. A-C Impedance Study

An equivalent electrical circuit that describes the electrode processes on different electrolytes, using porous Pt electrodes,is given. Diffusional processes are important and have to be presented by Warburg components in the circuit. Theoverall electrode process is rate limited by diffusion of atomic oxygen on the electrode surface for stabilized zirconia andsubstituted ceria (low PO2). On stabilized bismuth sesquioxide diffusion of atomic oxygen on the electrolyte surface is ratelimiting at high PO2 while at low PO2 another process, probably diffusion of electronic species in the electrolyte, is dominant.One of these processes plays a role too on substituted ceria at high PO2, where a charge transfer process is dominant. Theseresults are consistent with the mechanisms developed in part I of this paper

M/V in de kerk : vrouwelijke gaven en mannelijke ambten

Deputaten ’M/V in de kerk’ constateren dat vrouwen in de Gereformeerde Kerken (GK) steeds vaker taken vervullen die voorheen vooral of uitsluitend door mannen werden vervuld. Ze geven catechisatie, zijn scriba of notulist van de kerkenraad, doen pastoraal werk en vervullen allerlei diaconale taken. Ook zien we dat vrouwen een steeds grotere rol vervullen in de kerkelijke besluitvorming

High oxygen ion conduction in sintered oxides of the Bi2O3---Ln2O3 system

The conditions leading to optimum conductivity of the Bi2O3---Ln2O3 system were investigated. The highest conductivity was found for Ln = Er or Tm. Ordering in the oxygen lattice was investigated using neutron diffraction. Correlations were found between the neutron diffraction data and the conductivity

Preparation and properties of new oxygen ion conductors for use at low temperatures

Two new systems, Bi2O3---Er2O3 and ZrO2---Y2O3(CaO)---Bi2O3 were investigated. The first system has a homogeneous cubic, fluorite phase between 17.5 and 45.5 mol % Er2O3 and can be sintered to densities near 95% at 1200 K. At temperatures between 700 K and 1000 K the highest value of the a.c. oxygen ion conduction in this system is twice as much as the highest value found in the literature. In the second system concentrations of 1–3 mol % Bi2O3 act as an excellent sintering aid for ZrO2---Y2O3 and ZrO2---CaO samples which can be sintered to densities higher than 95% at temperatures of 1350 K. During this procedure a liquid ZrO2---Bi2O3 phase exists from which Bi2O3 partly evaporates with increasing sintering time. The oxygen ion conduction is little affected by the Bi2O3-rich second phase. The influence of annealing procedures up to 1570 K on the conduction in the ZrO2---Y2O3---Bi2O3 system is small despite weight losses up to 4%

Effect of grain boundaries on the conductivity of high-purity ZrO2---Y2O3 ceramics

Grain boundary conductivities are determined by complex impedance measurements (1–106 Hz) on high-purity ceramics prepared by the alkoxide synthesis and on less pure ceramics obtained from a commercial powder. The grain size was varied systematically in the region 0.36–55 μm. The grain boundary conductivity is strongly influenced by the grain size, impurities and cooling procedure. The grain boundary conductivity increases linearly with the grain size for small grain sizes (0.3 to 2–4 μm) and is constant for larger grain sizes. The calculated specific conductivity of the grain boundary for pure materials is about 100 times smaller than that of the bulk. The grain boundary thickness was estimated to be 5.4 nm. The activation energy of the grain boundary conductivity is 7 kJ mole−1 higher than of the bulk