296 CHEMICAL SENSORS: FUNDAMENTALS. VOLUME 3: POLYMERS & OTHER MATERIALS Table 6.1. Ionic conductivity of selected solid electrolytes I ONIC C ONDUCTOR YSZ (9 mol% Y 2 O 3 ) MSZ (15 mol% MgO) SrCeO 3 (5 mol% Yb) CaZrO 3 (10 mol% In) Nafion Na -alumina Sr -alumina C ONDUCTING I ON O 2- O 2- H + H + H + Na + Sr 2+ C ONDUCTIVITY (S cm -1 ) 0.12 0.038 0.1 0.06 0.01 (100% humidity) 0.02 4.2­10 -4 T EMPERATURE (K) 1273 1273 1000 1000 300 500 1573 A CTIVATION ENERGY (eV) 0.85 1.1 0.55 0.7 0.05 0.16 1.24 nature of the application. The conductivity at any other temperature can be calculated using Eq. (6.6) and the data provided in the table. It has been found by experience that the ionic conductivity must be reasonably high for a material to be applied successfully as an electrolyte in a sensor. An empirical value of 10 -3 S cm -1 or more is often considered as a guide. For example, 8 mol% yttria-stabilized zirconia, YSZ, is used at temperatures above 350°C, and is not suffi ciently conducting for use in sensors at lower temperatures. Lower-conductivity versions, such as 3 mol% partially yttria-stabilized zirconia and 15