Electrical conductivity and nonstoichiometry in doped Sr3Ti2O7

A series of doped Ruddlesden-Popper phases, of general formula Sr3Ti2-xMxO7 -delta (M = Al, Ga, Co), were synthesized and their electrical conductivity characterized as a function of temperature and oxygen partial pressure. Fo r fixed-valent dopants, p-type conductivity predominates at p(O-2) > 10(-5) atm, followed by a p(O-2)-independent electrolytic regime, and n-type elec tronic conductivity at very low p(O-2) The electrolytic regime exhibits act ivation energies in the range 1.7-1.8 eV. Doping with transition metals suc h as Co results in a very significant increase in fetal conductivity with a p-type conductivity at high p(O-2). Furthermore, an apparent ionic regime at intermediate p(O-2) is observed characterized by high conductivity (> 10 (-2) S/cm at 700 degrees C) and low activation energy (0.6 eV). This interp retation is consistent with iodometric measurements as interpreted by a def ect chemical model. Other measurements are in progress to confirm this conc lusion. (C) 1999 Elsevier Science Limited. All rights reserved.