Grain-boundary effect on conductivity

The grain-boundary conductivity could be improved by the addition of small amounts of transition-metal oxides, especially at intermediate temperatures. For example, 

Solid Oxide Fuel Cells Materials Properties and Performance 

FIGURE1.9 The grain boundary and bulk conductivities at 300°C for 8YSZ ceramics doped with ZnO with reference to the undoped YSZ sintered at the same temperature as a function of ZnO content [52]. 

FIGURE 1.10 Conductivity of zirconia stabilized with various dopants. 

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