**6. Magnesium–Zinc–Cerium Ternary Phase Diagram**

Experimental investigation and thermodynamic modeling of the Mg-Zn-Ce received considerable attention by many researchers [141–153]. However, the reported ternary phases and ternary solid solutions were confusing. Table 1 summarizes the reported ternary phases in the Mg-Zn-Ce system [151].


**Table 1.** Reported ternary phases in the Mg-Zn-Ce system in comparison with literature.

Ternary solid solution designated by Mg3Ce was reported by [149,152] where zinc atom substitutes magnesium atom in the binary Mg3Ce phase. The solubility of zinc in Mg3Ce and crystallographic data are shown in Table 2. Recently, this phase was verified in the work of Shi et al. [153].


**Table 2.** Crystallographic data and Zn solubility in Mg3Ce.

Ternary solid solution, denoted as τ<sup>3</sup> in the work of [152,153], was reported by [144,150] with a prototype of AlMnCu2. The percentage of zinc in this phase was 38 to 50 at.% [150], whereas Kevorkov and Pekguleryuz [148] reported this percentage as 45 to 50 at.%. Moreover, Mel'nik et al. [144] and Chiu et al. [149] reported that this phase contained 35 to 45, and 0 to 48 at.% Zn, respectively. It is worth noting that Chiu et al. [149] reported Mg3Ce solid solution with two different prototypes, namely BiF3 and AlMnCu2. Whereas Shi et al. [153] verified the existence of τ<sup>3</sup> and indicated the difficulty to distinguish between τ<sup>3</sup> and Mg3Ce because of the structural similarity. The authors of [153] declared the difficulty of detecting the difference using XRD. According to the BSE image in the work of [153], Mg3Ce showed diamond shape whereas τ<sup>3</sup> exhibited irregular shape. Meanwhile, τ<sup>3</sup> exists in equilibrium with Mg3Ce in accord with [152,153]. Reported comparisons between the crystallographic data and solid solubility for other ternary phases were summarized in the work of Chiu et al. [149] and Zhu et al. [152].

Liquidus projections of the Mg-Zn-Ce ternary phase diagram were calculated by [148–153]. The calculated ternary phase diagram by Chiu et al. [149] proposed that τ<sup>3</sup> and Mg3Ce were similar phase, which contradicts the findings in [152,153]. Moreover, ternary phase diagram presented by Zhu et al. [152] was an amendment to the work of Mostafa and Medraj [151]. Primary crystallization regions of ternary phases could not be found in the liquidus projection of Shi et al. [153]. Liquidus projections of Mg-Zn-Ce calculated by Zhu et al. [152] and Shi et al. [153] are shown in Figure 8a,b, respectively.

**Figure 8.** Calculated liquidus projections of Mg-Zn-Ce presented in (**a**) Zhu et al. [152] and (**b**) Shi et al. [153].
