Ternary hydrides have recently been predicted to exhibit exceptional superconducting properties under high pressure, positioning them as promising candidates for room-temperature superconductivity. In this work, we perform a systematic investigation of the Th-B-H system at 100 and 200 GPa using state-of-the-art structural prediction method combined with first-principles calculations. Our results identified seven thermodynamically stable compounds, namely ThBH, ${\mathrm{ThBH}}_7$, ${\mathrm{ThB}}_2{\mathrm{H}}_{10}$, ${\mathrm{ThB}}_2{\mathrm{H}}_3$, ${\mathrm{ThB}}_2{\mathrm{H}}_{13}$, ${\mathrm{Th}}_2{\mathrm{BH}}_{16}$, and ${\mathrm{ThB}}_6{\mathrm{H}}_6$, in which B atoms are bonded with H atoms, giving rise to diverse structural motifs, including ${\mathrm{BH}}_4$ tetrahedra, ${\mathrm{B}}_2{\mathrm{H}}_8$ (${\mathrm{H}}_4\mathrm{B}\text{−}{\mathrm{BH}}_4$) units, ${\mathrm{BH}}_6$ octahedra, an interpenetrating framework constructed from orthogonal zigzag ${\mathrm{BH}}_3$ chains and corrugated B-H layers. In addition to the existence of conventional atomic H, we uncover exotic hydrogen species, such as isolated ${\mathrm{H}}_5$ planar pentagons and ${\mathrm{H}}_4$ pyramidal units. Further electron-phonon coupling calculations reveal that nonclathrate hydride ${\mathrm{Th}}_2{\mathrm{BH}}_{16}$ exhibits a $T_c$ of 72 K at 200 GPa, which increases to 102 K upon decompression to 120 GPa. Moreover, the further results show hole doping could enhance superconductivity, leading to an increased $T_c$ of 115 K in the isostructural ${\mathrm{Th}}_2{\mathrm{BH}}_{15}$. These findings provide valuable insights for the design and synthesis of ternary hydrides with high-temperature superconductivity, particularly in rare-earth metal hydrides under high pressure.

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• BCS theory
• Band structure methods
• First-principles calculations