Through systematic structural predictions and electronic-structure analyses of La-Al intermetallic compounds at ambient pressure, we identify a previously unknown hexagonal phase, ${\mathrm{LaAl}}_5$. In this phase, planar Al-Al bonds assemble into a graphenelike sublattice, while adjacent Al layers are interconnected through additional Al-Al bonds. Extended structural searches of all rare-earth ($R$ = Sc-Lu) and selected actinide ($\mathit{AC}$ = Ac, Th, Pa, U, and Np) aluminides with the composition $(R/AC){\mathrm{Al}}_5$ reveal 16 dynamically stable compounds, confirming the robustness and universality of this graphenelike configuration. Electronic-structure calculations reveal that all these compounds are metallic, with conductivity arising from pronounced hybridization between $\mathrm{Al}\text{−}3p$ and $R/\mathit{AC}-d/f$ states near the Fermi level. The formation of $\sigma$-like Al-Al bonds is driven by electron transfer from $R/\mathit{AC}$ atoms to the Al sublattice, accompanied by redistribution of Al valence electrons. Furthermore, electron-phonon coupling calculations predict weak superconductivity in ${\mathrm{LaAl}}_5$, which is moderately enhanced in ${\mathrm{AcAl}}_5$. Gibbs free-energy calculations show that $(\mathrm{La}/\mathrm{Y}/\mathrm{Sc}){\mathrm{Al}}_5$ could become energetically stable at temperature below 800 K, a regime routinely accessible in aluminide synthesis. These findings provide direct evidence for the existence of graphenelike structures formed by Al atoms and establish a foundation for the experimental realization of this intriguing class of rare-earth aluminides.

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• Electronic structure
• Phase transitions
• Superconductivity
• Crystal structures
• First-principles calculations