Hydrogen ion conduction in iron-substituted strontium titanate, SrT1-xFexO3-x/2 (0 ≤ x ≤ 0.8)

Conduction of hydrogen species in selected compositions of SrTi1-xFexO3-x/2 (0 less than or equal to x less than or equal to 0.8) has been investigated by ac conductivity and concentration cell emf transport number measurements, as a function of p(O2), p(H2O), and temperature (500-1100 degreesC). The main contributions to the total conductivity are n-type electronic, dominating at low p(O2), ionic (oxygen vacancies) at intermediate p(O2), and p-type electronic at high p(O2). Hydrogen ion conduction is measurable, but the hydrogen containing species are minority defects in this system at the temperatures investigated, both in terms of concentration and conductivity. When the conditions are not too reducing, hydrogen ions are positive, assumed to be protons, H+. At lower p(O2). however, there is a change in the sign of the emf of the water vapour concentration cell, and thus apparently of the charge of the hydrogen-containing charge carrying species. This can be rationalised by the presence and migration of substitutionally dissolved hydride ions, H-, but it is questioned whether these can be stable under the conditions used.(C) 2001 Elsevier Science B.V. All rights reserved.