Electron-hole transport in (La0.9Sr0.1)0.98Ga0.8Mg0.2O3−δ electrolyte: effects of ceramic microstructure

The oxygen ion transference numbers of a series of (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3−δ (LSGM) ceramics with different microstructures, prepared by sintering at 1673 K for 0.5-120 h, were determined at 973-1223 K by a modified Faradaic efficiency technique, taking electrode polarization into account. In air, the transference numbers vary in the range 0.984-0.998, decreasing when temperature or oxygen partial pressure increases. Longer sintering times lead to grain growth and to the dissolution of Sr-rich secondary phases and magnesium oxide, present in trace amounts at the grain boundaries, into the major perovskite phase. This is accompanied with a slight decrease of the total grain-interior resistivity and thermal expansion, while the boundary resistance evaluated from impedance spectroscopy data decreases 3-7 times. The electron-hole transport in LSGM ceramics was found to decrease when the sintering time increases from 0.5 to 40 h, probably indicating a considerable contribution of acceptor-enriched boundaries in the hole conduction. Due to reducing boundary area in single-phase materials, further sintering leads to higher p-type conductivity. The results show that, as for ionic conductivity, electronic transport in solid electrolytes significantly depends on ceramic microstructure.