PROTONS IN LAERO3

The ac electrical conductivity of Ca-, Sr-, and Ba-doped LaErO3 has be en measured with the van der Pauw method as a function of P(H2O) (10(- 5)-10(-2) atm) P(O2) (10(-20)-1 atm), and temperature (500-1200-degree s-C). The total conductivity is modelled assuming a defect structure w hich comprises protons and oxygen vacancies compensating the acceptor dopants. Furthermore, it is assumed, and supported by EMF measurements , that the conductivity has contributions from protons, oxygen vacanci es, and electron holes. Data fitting allows the pre-exponential terms and enthalpies of mobilities and equilibrium constants to be determine d. The alkaline-earth-doped LaErO3 is mainly a protonic conductor at h igh P(H2O) and low P(O2) and temperature. The equilibrium constant for the reaction H2O(g) + V(o)'' = 2H(i)' + O(o)x is found to decrease wi th increasing temperature; oxygen vacancies are the dominant carrier a t high temperatures and protons at lower temperatures. The type of dop ant examined plays only a modest role on the type of defects that are preferred in this system.