Rare-earth (RE) elements exhibit diverse crystal structures and unique physicochemical properties under pressure, such as complex magnetic behavior and intriguing superconducting properties. Among them, lanthanum (La) exhibits enhanced superconductivity under compression. However, pressure-induced structural distortion and symmetry reduction modify its electronic properties, significantly reducing its superconducting temperature ($T_{\mathrm{c}}$) from its maximum value of 13.1 K at pressures exceeding 78 GPa. To optimize its $T_{\mathrm{c}}$, we employ an alloying strategy in this study, partially substituting La with yttrium (Y) to modulate its structural symmetry under high pressure, a key factor for $T_{\mathrm{c}}$. X-ray diffraction measurements reveal a phase transition in the La-Y alloy from an ambient hexagonal structure to a face-centered cubic phase at ∼11 GPa, maintaining high symmetry up to at least 170 GPa. Electrical transport measurements confirm that this cubic phase exhibits robust superconductivity, reaching a maximum $T_{\mathrm{c}}$ of 13.6 K at 65 GPa. These findings provide a platform for modulating structural symmetry and physical properties through alloying, highlighting the potential for discovering superior superconductivity in RE materials under extreme conditions.

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• Phase transitions
• Superconductivity
• Rare-earth alloys
• Solid solutions
• Crystal structures
• Resistivity measurements
• X-ray diffraction