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The high-pressure phases and superconductivity of CaYH12 have been explored by using a particle swarm optimization structure prediction methodology in combination with first-principles calculations. Our results show that CaYH12 becomes stable with a cubic Fd3m structure above 170 GPa, where metal atoms form body-centered-cubic (bcc) lattices and hydrogens occupy all the tetrahedral interstices of these bcc lattices, completing sodalitelike cages. The electron-phonon coupling calculations indicate that the Fd3m structure is a potential high-temperature superconductor, with a calculated Tc of 258 K at 200 GPa. Our current study provides a possibility for searching new high-Tc superconductors in ternary hydrides., The work was supported by National Natural Science Foundation of China (Grants No. 11604290 and No. 51732010), the Science Foundation for the Youth Topnotch Talent from Universities of Hebei Province (Grant No. BJ2017023), Funding Program for Recruited Oversea Scholars of Hebei Province (CL201729), and the Ph.D. Foundation by Yanshan University (Grant No. B970). A.B. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (FIS2016-76617-P) and the Department of Education, Universities and Research of the Basque Government and the University of the Basque Country (IT756-13).

We have performed a systematic study on the crystal structures and electronic properties of two ternary hydrides, YSH6 and LaSH6, under pressure, using the particle swarm optimization method and first-principles calculations. As a result of extensive structure searches, metallic YSH6 and LaSH6 are thermodynamically stable between 195-237 and 170-300 GPa, respectively. Interestingly, in YSH6 eight neighboring hydrogen atoms form octagons, and the octagons in different layers are connected by four sulfur atoms, forming a cagelike structure with a Y atom at the center, while those octagons in the same layer form polyphenylene-like chains via one shared side. In LaSH6, however, hydrogen atoms form both curved >H5> chains or straight chains when bonded to sulfur atoms. Furthermore, electron-phonon coupling calculations indicate that YSH6 and LaSH6 are promising superconductors with estimated Tc values of 91 and 35 K at 210 and 300 GPa, respectively. These results provide guidance for future experimental studies and stimulate more exploration on ternary hydrides., The work was supported by the National Natural Science Foundation of China (Grants No. 11604290 and No. 51732010), National Key R & D Program of China (Grant No. 2018YFA0703400), Funding Program for Recruited Oversea Scholars of Hebei Province (Grant No. CL201729), the Ph.D. Foundation by Yanshan University (Grant No. B970), and the Natural Science Research Project of Education Department of Anhui Province (KJ2018A0342). A.B. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (FIS2016-76617-P) and the Department of Education, Universities and Research of the Basque Government and the University of the Basque Country (IT756-13).