Prediction of enhanced superconductivity in cyclo-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mn>12</mml:mn></mml:msub><mml:mi>Bi</mml:mi><mml:mo>/</mml:mo><mml:mi>Pb</mml:m

Hydrogen-based compounds demonstrate high-temperature superconductivity under pressure, offering promising avenues for exploring metal hydrides with elevated critical temperatures (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>T</a:mi><a:mi mathvariant="normal">c</a:mi></a:msub></a:math>), while hydrides comprising <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msub><c:mi mathvariant="normal">H</c:mi><c:mn>2</c:mn></c:msub></c:math> molecular units were previously deemed unfavorable. Searching for new forms of hydrogen within metal hydrides promised a route for developing novel high-temperature superconductors. In this study, we utilized the evolutionary algorithm alongside first-principles calculations to investigate the high-pressure crystal structure of the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mi>Bi</e:mi><e:msub><e:mi mathvariant="normal">H</e:mi><e:mi mathvariant="normal">n</e:mi></e:msub></e:mrow></e:math> (<h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:mi>n</h:mi><h:mo>=</h:mo><h:mn>7</h:mn><h:mo>−</h:mo><h:mn>18</h:mn></h:mrow></h:math>) system. Notably, we discovered stable cyclo-<i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mrow><i:msub><i:mi mathvariant="normal">H</i:mi><i:mn>12</i:mn></i:msub><i:mi>Bi</i:mi><i:mo>/</i:mo><i:mi>Pb</i:mi></i:mrow></i:math> compounds in which the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:msub><k:mi mathvariant="normal">H</k:mi><k:mn>12</k:mn></k:msub></k:math> resembles cyclohexanelike cyclo-<m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msub><m:mi mathvariant="normal">H</m:mi><m:mn>12</m:mn></m:msub></m:math> rings. These compounds are stable above 180 GPa and exhibit a higher <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"><o:msub><o:mi>T</o:mi><o:mi mathvariant="normal">c</o:mi></o:msub></o:math> than <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"><q:mrow><q:mi>Bi</q:mi><q:msub><q:mi mathvariant="normal">H</q:mi><q:mn>8</q:mn></q:msub></q:mrow></q:math> composed of <s:math xmlns:s="http://www.w3.org/1998/Math/MathML"><s:msub><s:mi mathvariant="normal">H</s:mi><s:mn>2</s:mn></s:msub></s:math> units. In cyclo-<u:math xmlns:u="http://www.w3.org/1998/Math/MathML"><u:msub><u:mi mathvariant="normal">H</u:mi><u:mn>12</u:mn></u:msub></u:math>, the hydrogen has a slightly elongated intramolecular H-H length compared to <w:math xmlns:w="http://www.w3.org/1998/Math/MathML"><w:mrow><w:mi>Bi</w:mi><w:msub><w:mi mathvariant="normal">H</w:mi><w:mn>8</w:mn></w:msub></w:mrow></w:math>, while the intermolecular H-H distance is much shorter than in H cages, forming a resonant structure. The resonance led to in-/out-of-plane vibration modes for the six <y:math xmlns:y="http://www.w3.org/1998/Math/MathML"><y:msub><y:mi mathvariant="normal">H</y:mi><y:mn>2</y:mn></y:msub></y:math> units in cyclo-<ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML"><ab:msub><ab:mi mathvariant="normal">H</ab:mi><ab:mn>12</ab:mn></ab:msub></ab:math>, forming broad midfrequency vibrational bands and boosting the electron-phonon coupling. These findings highlight the cycloform of hydrogen-based hydrides as promising candidates for high <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML"><cb:msub><cb:mi>T</cb:mi><cb:mi mathvariant="normal">c</cb:mi></cb:msub></cb:math> superconductors, propelling further exploration of superconductivity in binary superhydrides with different forms of hydrogen. Published by the American Physical Society 2024