*3.1. Structural and Thermal Properties*

The amorphous nature of (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6 and 0.8) was confirmed by XRD. XRD patterns of (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6, and 0.8) bulk metallic glasses, as presented in Figure 1a, exhibit broad di ffraction peaks, and no traces of crystalline phases are detected. Therefore, the glassy nature of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6, and 0.8) bulk metallic glasses (BMG) was verified.

DSC curves of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6and 0.8) bulk metallic glasses are presented in Figure 1b. The main thermal events are the glass transition and subsequent crystallization. The glass transition temperatures *<sup>T</sup>*g, indicated by arrows in the figure, increase almost linearly with the substitution of Copper by Cobalt. While the Co-free ((La0.5Ce0.5)65Al10Cu25) alloy has a glass transition temperature of 372 K, the *T*g of (La0.5Ce0.5)65Al10(Co0.8Cu0.2)25 alloy increases up to 404 K. Crystallization temperatures *T*x show a less predictable behavior. Given that the di fference between the crystallization and glass transition temperatures is a parameter largely related to the glass stability, it is observed that (La0.5Ce0.5)65Al10(Co0.2Cu0.8)25 metallic glass is the most stable glass. The XRD patterns and DSC curves corroborate the amorphous properties of the studied alloys.

**Figure 1.** (**a**) XRD patterns of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6, and 0.8), as-cast state. (**b**) Differential scanning calorimeter (DSC) curves of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6, and 0.8) at a heating rate of 10 K/min. The glass transition temperature *Tg* of the different metallic glasses is pointed out in the figure.
