Transport Numbers in Stabilized Zirconia

Abstract

A simple theoretical t reatment of conduction in solids shows that apparent electron transport numbers determined by different exper imental techniques are not identical. The techniques considered for stabil ized zireonia were oxygen-transfer measurements and emf measurements on galvanic cells having oxygen at two different activities at the electrodes. Transport numbers for stabil izing cations can be determined by measuring compositional changes that result from passage of an electric urrent through the electrolyte. The principal current carr ier in stabil ized zirconia is known to be the oxide ion. The apparent electron transport number in an yttr ia-stabi l ized zirconia at 90O~176 is found to be ~0.005 in an oxidizing atmosphere and ~0.011 in a reducing atmosphere. The apparent transport number for yt t r ium ions is found to ~4 X 10-9. T ranspor t numbers in sol id oxides are of consid-erab le impor tance in the i r use as e lectro lytes in ga l-vanic cells for h igh- temperature thermodynamic measurements (1) and in the i r possib le use in fuel cells (2). Wagner (3) and Schot tky (4) are pr i-mar i ly respons ib le for the ear ly deve lopment of the theory of t ranspor t numbers in solids. Recent ly, Pa l 'guev and Neu imin (5), We issbar t and Ruka (6), and Schmalzre id (7) have repor ted results of t rans-por t-number measurements i ca lc ia-s tab i l i zed z i r-conia. Certa in aspects of t ranspor t-number deter-minat ion in such systems are discussed below, and some exper imenta l resul ts on y t t r ia-s tab i l i zed z i r-conia are presented.