Fig. 2a presents the density and gr

Fig. 2a presents the density and grain size behavior as a function of the composite composition. We obtained a high density for pure ZnO (98%±2%) that was in accordance with the fracture micrograph (Fig. 2b). This micrograph reveals a well-sintered sample and homogeneous grain growth of hexagonal geometry (0.9±0.5 μm). We attributed the unconformity of equivalent particle size (Fig. 1a) with the grain size of sintered ceramics to the tendency of the agglomeration of ZnO particles. The introduction of 10 wt% of BT in ZnO decreased the density (94%±2%) and the grain size (0.4±0.2 μm). Besides, the sintered microstructure did not incorporate the BT particles that are viewed in Fig. 2c as isolated particles (white grains). With 20 wt% of BT, the composite’s cold sinterability was drastically reduced, and the density was only 76%±2%. We observed that the grain size was ~0.35 μm for higher contents of BT. With 50% of BT, the microstructure was typical of green consolidated ceramic bodies and the cold sintering did not effectively promote mass transport. Fig. 2e presents an EDS compositional image for 50ZnO-50BT where the Ti elemental mapping was represented as blue points. We observed a homogeneous distribution of Ti atoms that can be extended for BaTiO3 distribution. The rapid density reduction together with the grain size reduction are indications that BT reduced the cold sinterability of ZnO ceramic. Some authors tend to separate the cold sintering into a two-stage process. In stage I, the compaction occurs by uniaxial mechanical force with enhanced lubricity between particles due to the liquid, and in stage II, the temperature is elevated under constant pressure and the solubility is enhanced 6), (7. During stage I, ~60% of density is expected for the compacted powder 12. The low density result for 10ZnO-90BT indicated that the cold sintering process (CSP) of this composition was limited to stage I and presented characteristics of a well-compacted powder. Finally, it should be recognized that the limit for cold sintering of these composites with high densities is 10 wt% of BT added to ZnO, at least for the experimental conditions reported here.