TRANSPORTED ENTROPY IN ZIRCONIA WITH 3 TO 12 MOLE PERCENT YTTRIA

Seebeck coefficients were measured for the cell (T1, p)Pt\O2(g)\YSZ\02(g)\Pt(T2, p). The electrolyte was yttria-stabilized zirconia (YSZ) and the content of yttria in the electrolyte varied between 3 and 12 mole percent (m/o). Thus tetragonal and cubic crystal structures were investigated. Different sintering temperatures and times were used in sample preparation to produce different grain sizes in the electrolyte. The reference temperature is T1 = 1000-degrees-C and T2 has been varied up to 1200-degrees-C. Two different oxygen pressures were used. The transported entropy of oxygen ions, S(O2-)* calculated from the Seebeck coefficient at 1273 K, is constant and equal to 42 +/- 2 J K-1 F-1 for all samples. The heat of transport q* is irrelevant to the Seebeck coefficient as q* is related to diffusion, which does not take place. The Thomson coefficient of the material is estimated to be 18 J K-1 F-1. This result is used to compare values for the transported entropy of oxygen ions, S(O2-)*, calculated from literature reports. Common expressions from thermoelectric theory are rejected on theoretical as well as experimental grounds.