From the refinement of the molar fraction of the two phases, we find a clear two-phase behavior on the Al-rich side (linear trend). From the extrapolation of the phase amounts, we find and intersect of the x axis at x = 0.69, indicating the limit of the miscibility gap. Thus, at low Zn content (0 ≤ x ≤ 0.69), the system consists of a 2-phase mixture of the NAC and NZC-type phases. When x exceeds 0.69, a solid solution in the NZC-type phase remains. The Zn, Na1, and Na2 occupancies were refined in this solid solution (0.69 ≤ x ≤ 1) and are shown in Figures and. As was already discussed in Section 3.2, Na⁺ ions in the Na1 (Wyckoff 4a) site are expected to be more mobile, and lower occupancies for Na1 compared to Na2 are observed across all compositions, suggesting that vacancies tend to form in the Na1 channel. For x < 0.75, the Na1 occupancy stabilizes close to 0.7, while the Na2 site is more (but not fully) occupied, close to 0.95. At x = 0.75, the difference between the two sites is smaller, with site occupancy of Na1 = 0.84(4) and Na2 = 0.91 (5), details see Table . Consistent with the solid solution limit (x = 0.69), Zn occupancies remain constant at 0.67(4) when the nominal x decreases to 0.625, indicating that the crystallization of the NAC phase is energetically more favorable than the further substitution of Al³⁺ in the NZC-type phase. Finally, Figure displays the refined Zn content against the nominal total Zn content x. Since the refined Zn content considers all free parameters (molar amount of NAC-and NZC-type phase and refined Zn content in each phase), the linear relationship with a slope of 1 along the diagonal strongly supports the reliability of our analysis.