We present the elastic and dynamical properties of YB4 from first-principles calculations. It is found that the optimized lattice constants and bulk modulus （182 GPa） agree well with the experimental data. The struc...We present the elastic and dynamical properties of YB4 from first-principles calculations. It is found that the optimized lattice constants and bulk modulus （182 GPa） agree well with the experimental data. The structural stability of tetragonal YB4 is confirmed by the calculated elastic constants and phonon spectra. YB4 holds a Debye temperature of 874 K and has small elastic anisotropy. The estimated hardness of YB4 is about 17 GPa, indicating that YB4 is a hard solid while not a superhard one.展开更多
As a fundamental thermodynamic variable, pressure can alter the bonding patterns and drive phase transitions leading to the creation of new high-pressure phases with exotic properties that are inaccessible at ambient ...As a fundamental thermodynamic variable, pressure can alter the bonding patterns and drive phase transitions leading to the creation of new high-pressure phases with exotic properties that are inaccessible at ambient pressure. Using the swarm intelligence structural prediction method, the phase transition of TiF_(3), from R-3c to the Pnma phase, was predicted at high pressure, accompanied by the destruction of TiF_6 octahedra and formation of TiF_8 square antiprismatic units. The Pnma phase of TiF_(3), formed using the laser-heated diamond-anvil-cell technique was confirmed via high-pressure x-ray diffraction experiments. Furthermore, the in situ electrical measurements indicate that the newly found Pnma phase has a semiconducting character, which is also consistent with the electronic band structure calculations. Finally, it was shown that this pressure-induced phase transition is a general phenomenon in ScF_(3), VF_(3), CrF_(3), and MnF_(3), offering valuable insights into the high-pressure phases of transition metal trifluorides.展开更多
Hydrogen-rich compounds are promising candidates for high-Tc or even room-temperature superconductors. The search for high-Tc hydrides poses a major experimental challenge because there are many known hydrides and eve...Hydrogen-rich compounds are promising candidates for high-Tc or even room-temperature superconductors. The search for high-Tc hydrides poses a major experimental challenge because there are many known hydrides and even more unknown hydrides with unusual stoichiometries under high pressure. The combination of crystal structure prediction and first-principles calculations has played an important role in the search for high-Tc hydrides, especially in guiding experimental synthesis. Crystal structure AnaLYsis by Particle Swarm Optimization(CALYPSO) is one of the most efficient methods for predicting stable or metastable structures from the chemical composition alone. This review summarizes the superconducting hydrides predicted using CALYPSO. We focus on two breakthroughs toward room-temperature superconductors initiated by CALYPSO: the prediction of high-Tc superconductivity in compressed hydrogen sulfide and lanthanum hydrides, both of which have been confirmed experimentally and have set new record Tc values. We also address the challenges and outlook in this field.展开更多
The recent observation of high critical temperature T_(c) in lanthanum and Yttrium hydrides confirms the key role of hydrogen cage(H-cage)in determining high superconductivity.Here,we present a new class of metastable...The recent observation of high critical temperature T_(c) in lanthanum and Yttrium hydrides confirms the key role of hydrogen cage(H-cage)in determining high superconductivity.Here,we present a new class of metastable H_(12) clathrate structures based on the icosahedral cI 24-Na that can be stabilized by incorporation of metal elements.Analysis shows that the charge transfer from metal atoms to H atoms contributes to forming the H_(12) clathrate.Nine dynamically stable structures are identified to exhibit superconductivity,and a maximum T_(c) of 28K is found in voids-doped Mo_(6)H_(24).Calculations reveal that the low T_(c) is attributed to the weak interaction between H atoms in each cage due to the long H–H distance.The current results provide a possible route to design H-cage containing superconductors.展开更多
Considering that pressure-induced formation of short,strong covalent bonds in light-element compounds can produce superhard materials,we employ structure searching and first-principles calculations to predict a new cl...Considering that pressure-induced formation of short,strong covalent bonds in light-element compounds can produce superhard materials,we employ structure searching and first-principles calculations to predict a new class of boron nitrides with a stoichiometry of BN_(2),which are stable relative to alpha-B and alpha-N_(2) at ambient pressure.At ambient pressure,the most stable phase has a layered structure(h-BN_(2)) containing hexagonal BN layers between which there are intercalated N_(2) molecules.At 25 GPa,a three-dimensional P4_(2)/mmc structure with single N-N bonds becomes the most stable.Dynamical,thermal,and mechanical stability calculations reveal that this structure can be recovered under ambient conditions.Its calculated stress-strain relations demonstrate an intrinsic superhard nature with an estimated Vickers hardness of ~43 GPa.This structure has a potentially high energy density of ~4.19 kJ/g.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11347007, the Colleges and Universities in Jiangsu Province Natural Science Research Project under Grant No 14KJB460013, and the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘We present the elastic and dynamical properties of YB4 from first-principles calculations. It is found that the optimized lattice constants and bulk modulus （182 GPa） agree well with the experimental data. The structural stability of tetragonal YB4 is confirmed by the calculated elastic constants and phonon spectra. YB4 holds a Debye temperature of 874 K and has small elastic anisotropy. The estimated hardness of YB4 is about 17 GPa, indicating that YB4 is a hard solid while not a superhard one.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12034009, 91961204, and 11974134)。
文摘As a fundamental thermodynamic variable, pressure can alter the bonding patterns and drive phase transitions leading to the creation of new high-pressure phases with exotic properties that are inaccessible at ambient pressure. Using the swarm intelligence structural prediction method, the phase transition of TiF_(3), from R-3c to the Pnma phase, was predicted at high pressure, accompanied by the destruction of TiF_6 octahedra and formation of TiF_8 square antiprismatic units. The Pnma phase of TiF_(3), formed using the laser-heated diamond-anvil-cell technique was confirmed via high-pressure x-ray diffraction experiments. Furthermore, the in situ electrical measurements indicate that the newly found Pnma phase has a semiconducting character, which is also consistent with the electronic band structure calculations. Finally, it was shown that this pressure-induced phase transition is a general phenomenon in ScF_(3), VF_(3), CrF_(3), and MnF_(3), offering valuable insights into the high-pressure phases of transition metal trifluorides.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11804128 and 11722433)the Qing Lan Project of Jiangsu Province,Chinathe Six Talent Peaks Project of Jiangsu Province,China
文摘Hydrogen-rich compounds are promising candidates for high-Tc or even room-temperature superconductors. The search for high-Tc hydrides poses a major experimental challenge because there are many known hydrides and even more unknown hydrides with unusual stoichiometries under high pressure. The combination of crystal structure prediction and first-principles calculations has played an important role in the search for high-Tc hydrides, especially in guiding experimental synthesis. Crystal structure AnaLYsis by Particle Swarm Optimization(CALYPSO) is one of the most efficient methods for predicting stable or metastable structures from the chemical composition alone. This review summarizes the superconducting hydrides predicted using CALYPSO. We focus on two breakthroughs toward room-temperature superconductors initiated by CALYPSO: the prediction of high-Tc superconductivity in compressed hydrogen sulfide and lanthanum hydrides, both of which have been confirmed experimentally and have set new record Tc values. We also address the challenges and outlook in this field.
基金Supported by the National Natural Science Foundation of China(Grant Nos.12074154,11722433,11804128,11804129,and 11904142)the Qing Lan Project of Jiangsu Province.
文摘The recent observation of high critical temperature T_(c) in lanthanum and Yttrium hydrides confirms the key role of hydrogen cage(H-cage)in determining high superconductivity.Here,we present a new class of metastable H_(12) clathrate structures based on the icosahedral cI 24-Na that can be stabilized by incorporation of metal elements.Analysis shows that the charge transfer from metal atoms to H atoms contributes to forming the H_(12) clathrate.Nine dynamically stable structures are identified to exhibit superconductivity,and a maximum T_(c) of 28K is found in voids-doped Mo_(6)H_(24).Calculations reveal that the low T_(c) is attributed to the weak interaction between H atoms in each cage due to the long H–H distance.The current results provide a possible route to design H-cage containing superconductors.
基金Supported by the National Natural Science Foundation of China(Grant Nos.12074154,11904142 and 11722433)the Science and Technology Project of Xuzhou(Grant No.KC19010)+1 种基金the Six Talent Peaks Project and the 333 High-Level Talents Project of Jiangsu Provincethe Natural Science Research Projects of Colleges and Universities in Jiangsu Province(Grant No.19KJB140001)。
文摘Considering that pressure-induced formation of short,strong covalent bonds in light-element compounds can produce superhard materials,we employ structure searching and first-principles calculations to predict a new class of boron nitrides with a stoichiometry of BN_(2),which are stable relative to alpha-B and alpha-N_(2) at ambient pressure.At ambient pressure,the most stable phase has a layered structure(h-BN_(2)) containing hexagonal BN layers between which there are intercalated N_(2) molecules.At 25 GPa,a three-dimensional P4_(2)/mmc structure with single N-N bonds becomes the most stable.Dynamical,thermal,and mechanical stability calculations reveal that this structure can be recovered under ambient conditions.Its calculated stress-strain relations demonstrate an intrinsic superhard nature with an estimated Vickers hardness of ~43 GPa.This structure has a potentially high energy density of ~4.19 kJ/g.
