High-temperature superconductivity in Th-B-H systems via nonclathrate design

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, ThBH₇, ThB₂H₁₀, ThB₂H₃, ThB₂H₁₃, Th₂BH₁₆, and ThB₆H₆, in which B atoms are bonded with H atoms, giving rise to diverse structural motifs, including BH₄ tetrahedra, B₂H₈ (H₄B-BH₄) units, BH₆ octahedra, an interpenetrating framework constructed from orthogonal zigzag BH₃ chains and corrugated B-H layers. In addition to the existence of conventional atomic H, we uncover exotic hydrogen species, such as isolated H₅ planar pentagons and H₄ pyramidal units. Further electron-phonon coupling calculations reveal that nonclathrate hydride Th₂BH₁₆ exhibits a Tc 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 Tc of 115 K in the isostructural Th₂BH₁₅. 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.