Sps. Badwal, GRAIN-BOUNDARY RESISTIVITY IN ZIRCONIA-BASED MATERIALS - EFFECT OF SINTERING TEMPERATURES AND IMPURITIES, Solid state ionics, 76(1-2), 1995, pp. 67-80
The role of grain boundary phases and their influence on grain boundar
y resistivity in ZrO2-based electrolyte systems have been investigated
by impedance spectroscopy and microstructural analysis. The effect of
sintering temperature on the grain boundary and intragrain resistivit
y of seven ZrO2-Y2O3 systems varying in impurity and Y2O3 contents has
been described. For each system six to eight different sintering temp
eratures between 1200 and 1700 degrees C were used. Changes in the int
ragrain resistivity with increasing sintering temperature were small a
nd related mainly to densification of the ceramic. The grain boundary
resistivity exhibited a complex behaviour which was different for diff
erent ceramics and varied with the impurity content. The grain boundar
y resistivity versus sintering temperature plots showed inflection or
peaks. This type of behaviour has been attributed to the dynamic natur
e of the grain boundary phase (composition, location and wetting prope
rties all of which change with the sintering temperature and atmospher
e, cooling rates from the sintering temperature and subsequent heat tr
eatments) and the amount and type of impurities in the starting powder
s. The activation energy for oxygen-ion conduction across grain bounda
ries was independent of the impurity content or nature of the glassy p
hase. It has been shown that the oxygen-ion conduction across grain bo
undaries takes place through direct grain to grain contact rather than
through the intermediate grain boundary glassy phase which has an ext
remely low oxygen-ion conductivity.