Suchergebnisse

The crystal structures and properties of boron-silicon (B-Si) compounds under pressure have been systematically explored using particle swarm optimization structure prediction method in combination with first-principles calculations. Three new stoichiometries, B2Si, BSi, and BSi2, are predicted to be stable gradually under pressure, where increasing pressure favors the formation of silicon rich B-Si compounds. In the boron-rich compounds, the network of boron atoms changes from B12 icosahedron in the ambient phases to the similar buckled graphenelike layers in the high-pressure phases, which crystalize in the same P¯3m1 symmetry but with different numbers of boron layers between adjacent silicon layers. Phonon calculations show that these structures might be retained to ambient conditions as metastable phases. Further electron-phonon coupling calculations indicate that the high-pressure phases of boron-rich compounds might superconduct at 1 atm, with the highest Tc value of 21 K from the Allen-Dynes equation in P¯3m1 B2Si, which is much higher than the one observed in boron doped diamond-type silicon. Moreover, further fully anisotropic Migdal-Eliashberg calculations indicate that B2Si is a two-gap anisotropic superconductor and the estimated Tc might reach up to 30 K at 1 atm. On the silicon-rich side, BSi2 is predicted to be stable in the CuAl2-type structure. Our current results significantly enrich the phase diagram of the B-Si system and will stimulate further experimental study. ; The work was supported by Fostering Program of Major Research Plan of NSFC (91963115), National Key R & D Program of China (2018YFA0703400), National Natural Science Foundation of China (No. 51732010, 11674176, 11874224), Funding Program for Recruited Oversea Scholars of Hebei Province (Grant No. 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 (Grant No. FIS2016-76617-P) and the Department of Education, Universities and Research of the Basque Government and the University of the Basque Country (Grant No. IT756-13). ; Peer reviewed

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).

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).