As outlined in literature, the subs

As outlined in literature, the substantial benefits of CSP was to reduce sintering/post heat treatment temperature required to achieve a dense material with high conductivity level compared to the conventional method. In this work, experiments were performed by lowering the annealing temperature, and even by eliminating the post heat treatment. As an initial result, the comparison between an as-CSP pellet (obtained under 375 MPa at 180 °C using 5 wt% of water) and a green pellet that was just dry pressed demonstrates a great improvement in the relative density from 62 % to 83 %. The SEM observations presented on Fig. 9A-B confirm this result, showing more aggregated particles with the formation of densification necks in the case of CSP (Fig. 9B). Fig. 10A shows that a further annealing at 1200 °C can enhance the densification (94 %) leading to a great increase of the conducting properties in the entire temperature range compared to the non-post annealed cold sintered pellet. As mentioned previously, at low temperature, the contribution of bulk and grain boundary can be clearlydistinguished and seems to be more important for the non-sintered pellet. In contrast, at high temperature we can only determine the total resistance of the electrolyte. At 685 °C for instance a decrease of the total electrolyte resistance from 84 to 5 Ω.cm² is observed after annealing at 1200 °C. Fig. 10B-C collects the evolution of grain and grain boundary conductivity before and after annealing in the temperature range within which they can be determined. The post heat treatment can drastically increase the conductivity of grain and especially grain boundary. To explain this evolution trend, the cross section microstructure of the two samples was investigated by SEM and illustrated in Fig. 9B-C. For the non-sintered sample, a small grain size with some distributed pores can be observed, consistent with the high measured total resistances. After annealing at 1200 °C, the sample showed a grain growth and well interconnected particle with clear edges resulting in a decrease of the total resistances.