# Polymorphism in $Ca(BH_{x})_{2}$: Towards superconductivity in ternary hydrides.

Di Cataldo S., von der Linden W., Boeri L.

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Hydrides at high pressures are the most promising materials to achieve room-temperature superconductivity. The main open challenge is to lower the pressures currently needed to achieve high $T_c$. As most binaries have been explored, the next natural step is to consider ternary systems. In this work we investigate the high pressure thermodynamics of $Ca(BH_{x})_{2}$ with evolutionary crystal structure prediction and density functional theory. $Ca(BH_{x})_{2}$, already known for its hydrogen storage properties, shows carbon-like polymorphism with strong covalent bonding: a key element for high temperature superconductivity. Among the predicted phases, we identify promising candidates for high-$T_c$ superconductivity.