First-principles investigation of Sc-III/IV under high pressure

Abstract

Using ab initio evolutionary structure prediction method in conjunction with density functional theory, we performed a systematic investigation on the structural transition of elemental scandium under pressure up to 250 GPa. Our prediction successfully reproduced several allotropes which have been reported in the previous literature, including the Sc-I, Sc-II and Sc-V. Moreover, we observed a series of energetically degenerate and geometrically similar structures at 110-195 GPa, which are likely to explain the unsolved phases III and IV reported by Akahama [Phys. Rev. Lett., 94, 19, 195503, (2005)]. A detailed comparison on powder X-ray diffraction pattern (PXRD) suggested that the Ccca-20 phase may account for the observed Sc-III, while Sc-IV is likely to be explained by a mixture of multiple energetically competing structures. We also used the candidate Sc-III structure as the model system to explore its superconducting behavior under pressures between 80-130 GPa. The predicted superconducting transition temperature Tc values are in satisfactory agreement with previous experimental results. *

Pressure tuned incommensurability and guest structure transition in compressed scandium from machine learning atomic simulation

“…S1 in the ESI †. In addition to our previous work, 41 SSW–NN enabled much extensive structural search and the global minima structure of the Ccca-type phase eventually reached an agreement with the experiment, 41 which is not the P 4 1 2 1 2 structure. 42 By comparing the energy, we found that the P 4 1 2 1 2 structure has a higher energy than the Ccca structure.…”

Record high $T_{\rm c}$ and robust superconductivity in transition metal $δ$-Ti phase at megabar pressure

“…Unlike the simple alkaline (earth) metals, in which N (E F ) is dominated by s states, the T c of TMs usually exhibits a highly nonlinear dependent T c on pressure [11]. Such complexity is associated with the nature of their partially filled d electrons and SPT under pressure [11,74], which is consistent with our results.…”

Superconductivity above 30K Achieved in Dense Scandium

“…[4,[9][10][11][12][13][14] The structure instability associated with the pressure induced tendency and occurrence of phase transitions favors superconductivity because of the lattice softening enhanced electron-phonon coupling strength. [9] The crystal structure and physical properties of Sc metal under pressure were examined in previous studies, [15][16][17][18][19][20][21][22][23][24] which showed that Sc has the hcp structure (Sc I) under ambient conditions, and pressure generates four structural transitions at about 23, 104, 140, and 240 GPa, respectively, producing high-pressure phases of Sc II, Sc III, Sc IV, and Sc V, respectively. [17][18][19] Sc II phase crystallizes in an incommensurate composite structure comprising a body centered host structure and a 𝐶 face centered guest structure, [18] and Sc V phase has a hexagonal lattice consisting of six screw helical chains, [17] while Sc III and Sc IV phases are not fully determined.…”

“…[9] The crystal structure and physical properties of Sc metal under pressure were examined in previous studies, [15][16][17][18][19][20][21][22][23][24] which showed that Sc has the hcp structure (Sc I) under ambient conditions, and pressure generates four structural transitions at about 23, 104, 140, and 240 GPa, respectively, producing high-pressure phases of Sc II, Sc III, Sc IV, and Sc V, respectively. [17][18][19] Sc II phase crystallizes in an incommensurate composite structure comprising a body centered host structure and a 𝐶 face centered guest structure, [18] and Sc V phase has a hexagonal lattice consisting of six screw helical chains, [17] while Sc III and Sc IV phases are not fully determined. [19] Previous work reported that Sc starts to show superconductivity at 21 GPa with 𝑇c ∼ 0.35 K. [21] With further compression, 𝑇c reaches as high as 19.6 K at 107 GPa, which occurs just at the phase boundary of Sc II and Sc III.…”

“…[17][18][19] Sc II phase crystallizes in an incommensurate composite structure comprising a body centered host structure and a 𝐶 face centered guest structure, [18] and Sc V phase has a hexagonal lattice consisting of six screw helical chains, [17] while Sc III and Sc IV phases are not fully determined. [19] Previous work reported that Sc starts to show superconductivity at 21 GPa with 𝑇c ∼ 0.35 K. [21] With further compression, 𝑇c reaches as high as 19.6 K at 107 GPa, which occurs just at the phase boundary of Sc II and Sc III. However, 𝑇c was reported to drop to ∼ 10 K when pressure is further increased and Sc III phase appears.…”