Improved total conductivity of nanometric samaria-doped ceria powders sintered with molten LiNO₃ additive

Nanometric 20% molar Sm-doped ceria (SDC20) powders were synthesized by co-precipitation in the presence of N, N, N′, N′ tetramethylethylendiamine (TMEDA). SDC20 powders were sintered using lithium nitrate salt in various concentrations (0.1, 1, 3, and 10 mol% with respect to the SDC20 total moles) as an additive to promote the liquid phase sintering and without additive for comparison. The addition of the Li salt allowed reducing significantly the sintering temperature of SDC. Electrochemical impedance spectroscopy (EIS) measurements were performed to estimate the contribution of grain boundary and bulk to the electrical conductivity in different sintering conditions. Liquid phase sintering allowed to produce dense samples with enhanced ionic conductivity especially at the grain boundary when compared to the samples sintered without additive. The additive liquid phase was evaporated in large part at the high temperatures throughout the sintering process. Residual extra phases were segregated at the grain boundary, generated probably by reaction of the Li salt with impurities, which were removed by a chemical etching.