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 tam. The grain boundary conductivity is strongly influenced by the gsain size, impurities and cooling procedure. The grain boundary conductivity increases linearly with the grain size for small grain sizes (0.3 to 2-4 tam) 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 rim. The activation energy of the grain boundary conductivity is 7 kJ mole -1 higher than that of the bulk. 0 378-5963]82/0000-0000/$ 02.75

The effect of low concentrations of Fe203, AI203 and Bi203 on the sintering behaviour of (ZrO2)o.83 (YO1.s)o.17, made by alkoxide synthesis, has been investigated. The best results are achieved with Bi203 as a sinter agent and a relative density of 95% is obtained at 1200 K. The effects of these impurities on the electrical conductivity of the bulk and the grain boundaries has been investigated using frequency dispersion analysis (101-106 Hz). All investigated impurities have a negative influence on both the bulk and grainboundary conductivity. For Fe203 and AI203 grain-boundary segregation factors of about two are calculated.

The phase diagram of the Bi2 O3-Er2 O3 system was investigated. A monophasic fc c structure was stabilized for samples containing 17.5-45.5 mol% Er2 03. Above and below this concentration range polyphasic regions appear. The fcc phase showed high oxygen ion conduction. The ionic transference number is equal to one for specimens containing 30 mol% Er2 03 or less, while an electronic component is introduced at low temperatures for specimens containing 40-60 mol% Er2 03. Between 673 K and 873 K a maximum in the conductivity was found at 20 mol% Er2 03. (Bi2Oa)o~o(Er203)o.2o is found to be the best oxygen ion conductor so far known. The conductivity at 773 K and 973 K is 2.3 YZ-1 m-~ and 37 ~2-1 m-1 respectively. These values are 2-3 times higher than the best oxygen ion conductor reported for substituted Bi2 O3 systems and 50-100 times higher than those of stabilized zirconia (Zr02)o.915 (Y203)o.oss at corresponding temperatures.

The phase diagram of the Bi203-Dy203 system was investigated. A monophasic fcc structure was stabilized for samples containing 28.5-50.0 mole percent (m/o) Dy203. Above and below this concentration range polyphasic regions appear. The fcc phase showed high oxygen ion conduction. The ionic transference number is equal to one for specimens containing 28.5-40.0 m/o Dy203, whereas an electronic component is introduced at low temperatures for specimens containing 50.0 m/o Dy203. The conductivity of(Bi203)0.715 (Dy203)0.2s5 is 0.71 ~-1m-1 and 14.4 a-lm-1 at 773 and 973 K, respectively. Relations were found between the ionic radius, the conductivity, and the minimum concentration of lanthanide necessary to stabilize the fcc phase. It is concluded that the highest ionic conductivity will be found in the system Bi20~-Er203 or Bi2Os-Tm203. From a study of relations between the activation energy, log ~o and the composition it is concluded that two conductivity mechanisms play a role.

The electrode behavior of Ptosputtered and PT-gauze electrodes on ZrO2-Y203, Bi20~-Er20.~, and CeO~-Gd203 solid electrolytes was investigated by means of d-c measurements in the temperature region of 770-1050 K and in the oxygen partial pressure region of 10 -~ -1 atm O2 using N2-O2 mixtures. On these different materials the same electrode morphology was realized and was preserved during the subsequent experiments. The electrode process is strongly influenced by the nature of the electrolyte. The electrode resistance for Pt electrodes on Bi203-Er203 was found to be many times lower than on ZrO2-Y20~ and CeO2-Gd20~. On zirconia-and ceria-based materials-diffusion of atomic oxygen on the Pt electrode is the rate-determining step in the electrode process, whereas for bismuth sesquioxide-based materials diffusion on the oxide surfaces is rate determining.There is a considerable interest in solid electrolytes for use in oxygen sensors, oxygen pumps, and high temperature fuel cells. In these applications the electrode polarization and the electrolyte resistance both play an important role. These effects influence the response of an oxygen sensor and give rise to energy losses and therefore to a decreased efficiency, of oxygen pumps and fuel cells. Many studies are performed on electrode processes. However, the dominant elementary steps of the overall process are still unknown in most cases.The kinetics of the electrode process is strongly influenced by the electrode structure (1-6), electrode material (4, 5, 7-9), and the electrolyte (4, 5, 7). Information about the role of the electrolyte in the electrode process is very scarce and is limited to the role of the dopant. Schouler (4) found that the oxygen partial pressure dependence of the electrode resistance of a sputtered platinum electrode depends on the Y203 content of the ThO2 electrolyte. Fabry and Kleitz (7) found that the activation energy of the electrode resistance of a point electrode on calcia-stabilized zirconia is higher than that on yttria-stabilized zirconia. Wang anal Nowick (5) reported that the exchange current of a Pt-paste electrode is not influenced by the nature and the. concentration of the dopant of the CeO2 electrolyte.Even less attention is paid to the influence of the nature of the electrolyte on the overall electrode proi Present address: