Long-range structural characterization of the CSP sintered ZnO ceramics has been carried out by means of XRD. Possible residual phases or structural modifications of the ZnO lattice in the samples prepared under the CSP conditions have been evaluated. Figure 1a shows the XRD patterns related to samples prepared by CSP with different fractions of NPs, as well as those prepared by the CN method from pure MPs and NPs, for comparison. In all cases, only the wurtzite reflections are identified [21], and no other phases are detected within the detection limit. In addition, no significant variations are found in the diffraction pattern between the dense ceramics obtained by CSP varying the percentage of ZnO NPs and those obtained by the CN technique. However, modifications on the crystallite size are recognized (see Figure 1b) depending on the sintered conditions and the starting powder. For the samples prepared by the CN method, a significant increase of the crystallite size is observed, from circa (ca.) 90 nm and ca. 32 nm for starting MPs and NPs, respectively, to 180 nm for sintered CN micro and 90 nm for sintered CN nano (see Figure 1b). For the sintered CSP ceramics, the crystallite size reaches a maximum value of ca. 143 nm for a NPs percentage of 5-10 wt% (CSP n5 and CSP n10), which is higher than the crystallite size of the starting MPs, but does not reach the value obtained for the CN micro. As the NPs percentage increases in the starting powder, the ceramic crystallite size decreases up to ca. 47 nm for CSP n100, indicating a low crystallite size growth related to the starting ZnO NPs (32 nm).