Fig. 3 compares the microstructures

Fig. 3 compares the microstructures of the as-cold-sintered ceramics made using the uncoated powders and coated powders. Fig. 3(a) and the higher-resolution Fig. 3(b) show that, in the as-cold-sintered ceramics made using uncoated powder, most of the particles are rectangle shaped and do not closely connect with each other. Particles made from the coated powder 1-5 have a deformation that facilitates close packing in the ceramic and thereby enhances the density of the ceramic [Fig. 3(c) and 3(d)]. The deformation of the particle confirms the speculation based on the TEM analysis that, after coating, the BaTiO3 surface easily decomposes and dissolves in the liquid phase. The other ceramics made from the coated powders 2-5 and 3-5 lead to a similar situation (data not shown).