New Mixed Conductors Based on Doped Layered Perovskites

摘要

A series of doped Rudlesden-Popper phases, of general formula Sr_3TI_(2-x)M_xO_(7-#delta#), were synthesized and their electrical conductivity characterized as a function of temperature and oxygen partial pressure. For fixed-valent dopants, p-type ocnductivity predominates at p(O_2)>10~(-5) atm, folllowed by a p(O_2)-independent electrolytic regime, and n-type electronic conductivity at very low p(O_2). The electrolytic regime exhibits activation energies in the range 1.7-1.8 eV. Doping with transition metals such as Co results in a very significant increase in total ocnductiivty with a p-type ocnductivity at high p(O_2). Furthermore, an apparent ionic regime at intermediate p(O_2) is observed, characterized by high conductivity and low activation energy. This interpretation is consistent with iodometric measurements as interpreted by a defect chemical model. Other measuremens are in progress to confirm this conclusion.