Cold sintering process of ZnO ceramics: Effect of the nanoparticle/microparticle ratio

We show the efficiency in the preparation of >95 % dense ZnO ceramics by cold sintering process through the incorporation of ZnO nanoparticles in the 1−10 wt% range at temperatures of 170 °C, pressures of 750 MPa and a pellet height/diameter ratio of 0.38. Morphological, structural and physical properties are dependent on the amount of ZnO nanoparticles incorporated into the system. After the densification by cold sintering process, ZnO ceramics show a reduction of the average valence indicating the deficiency of oxygen, similar to ceramics sintered by the conventional route. Besides, the generation of structural disorder and modifications into the ZnO lattice are identified in sintered ceramics, inducing intrinsic defects related to the loss of oxygen ions, the diffusion of zinc and zinc vacancies, which depend on the sintering process and the starting powders. These characteristics influence the final functional properties of the sintered ZnO ceramics, such as the visible photoluminescence signal.