Nonetheless, it is known that halide solid electrolytes synthesized by ball milling may contain an amorphous phase, which may or may not play a role in the conductivity. To verify this possibility, the amorphous fraction of our samples has been determined using an internal reference. The analysis conducted with Al2O3 and Si internal references is reported in Figure . Indeed, our samples contain an amorphous phase ranging from 30% for NAC to 50% for NZC. The amount of amorphous phase is similar in all samples and increasing from NAC to NZC. The fact that our Rietveld analysis led to consistent Na and Zn contents in the crystalline part of the samples suggests that the crystalline and amorphous phases have similar compositions and possibly local structures. To verify that our structural analysis also holds at a more local scale, we employ Na magic angle spinning (MAS) ss-NMR, and the results are gathered in Figure . The NMR data further confirms that NaAlCl4 does not appear to be doped with Zn 2+ . As shown in Figure through the unchanged peak position (-14.2 ppm) and quadrupolar line shape of Na1, the local environment of Na in NAC is similar for all the compositions. With varying amounts of Zn (x) only the intensity of the peak changes following the phase ratios extracted from Rietveld refinements (Fig. ). The spectra obtained for NZAC (x = 0, 0.045, 0.25, 0.5, 0.75, 1) are also shown in Figure . The 23 Na MAS NMR spectrum of NZC (x = 1) displays two Na signals at 4.8 and 0.4 ppm with rather small apparent quadrupolar coupling constants of CQ = 0.7 MHz (η~0.5) and 0.5 MHz (η~0), respectively, which are assigned to the Na1 and Na2 sites in NZC. These signals related to the NZC phase appear even at x = 0.045, indicating that Zn²⁺ prefers to form the NZC phase rather than substitute for Al³⁺ in NAC. The significant peaks of NZC are distinguishable for x values ranging from 0.045 to 1. However, for samples x = 0.75, x = 0.5, and x = 0.25, additionally, a distribution of signals appears between 0 and -10 ppm indicating the presence of Na environments, which can be explained neither by pure NZC nor NAC. As we will discuss in the following, these environments are related to Na in the Al-doped NZC phase (NZAC).