ON THE UNIQUE PROPERTIES OF HETEROGENEOUS SOLID ELECTROCHEMICAL-CELLS

Heterogeneous solid electrochemical cells that contain two mixed ionic -electronic conductors (MIECs) exhibit quite unexpected I-V relations when the two MIECs conduct ionic defects having different absolute val ues of their effective charge \z\. For example, the larger voltage dro p need not occur on the MIEC with the larger resistance to electronic (electron/hole) current. When the ionic transference number of one of the two MIECs is close to unity and its resistance to electronic curre nt is large enough, then a simple relation is imposed on the ionic and electronic currents in the other MIEC. This is an ambipolar motion of ionic and electronic charge carriers with a non zero total current. T he effect on the I-V relations of adding a solid electrolyte in series with a MIEC, conducting defects with different \z\, is discussed in d etail, including the implications on ionic conductivity measurements.