Characteristics of transition metal oxide doping of YSZ: structure and electrical properties

Abstract

TiO₂, Mn₂O₃, Tb₄O₇, Nb₂O₅ and WO₃ can be doped into yttria-stabilised zirconia (YSZ) and from solid-state solutions. Five basic characteristics are found: (1) The phase of zirconia can be controlled by changing the oxygen vacancy concentration by doping. Dopants with valences lower than four tend to increase the oxygen vacancy concentration [V_O] and may convert ZrO₂· 3Y₂O₃ from the tetragonal to the cubic phase; dopants with valences higher than four tend to reduce [V_o] and may convert ZrO₂· 8Y₂O₃ from the cubic phase to the tetragonal phase. (2) p- or n-type conducting behaviour of the semiconducting dopant is maintained regardless of the change in the chemical environment. It is shown that the oxygen partial pressure dependence of the concentrations of holes and electrons is mainly determined by the dopants, i.e., the type and amount of transition metal oxide and yttria, which is an amphoteric semiconductor. (3) The ionic conductivity decreases when large amounts of dopants cause local lattice distortion. (4) The diffusion coefficients of electrons and ions are correlated. (5) The electrochemical redox potential of the dopant shows no obvious change when it is doped onto zirconia.