New Helical Chain Structure for Scandium at 240 GPa

Akahama, Yuichi; Fujihisa, Hiroshi; Kawamura, Haruki

doi:10.1103/physrevlett.94.195503

Cited by 65 publications

(69 citation statements)

References 20 publications

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“…Sc falls somewhat out of line since it transforms at ∼ 23 GPa from the hcp to an incommensurate host-guest structure [30,31] instead of to the canonical Sm-type structure. In fact, recent X-ray diffraction experiments on Sc to 297 GPa reveal four successive structure changes, the final being to a new helical chain structure above 240 GPa [32]. It has been suggested that the differences between Sc and the other trivalent d-electron metals may arise at least in part from the changes in electronic structure associated with the complete absence of delectrons in Sc's ionic core, thus allowing its 3d valence electrons to penetrate further into the core region (no orthogonality condition) and thus to assume a higher degree of localization [33,34].…”

Section: Resultsmentioning

confidence: 99%

Pressure-induced superconductivity in Sc to74GPa

Hamlin

Schilling

2007

Phys. Rev. B

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Using a diamond anvil cell with nearly hydrostatic helium pressure medium we have significantly extended the superconducting phase diagram T c (P ) of Sc, the lightest of all transition metals. We find that superconductivity is induced in Sc under pressure, T c increasing monotonically to 8.2 K at 74.2 GPa. The T c (P ) dependences of the trivalent d-electron metals Sc, Y, La, and Lu are compared and discussed within a simple s → d charge transfer framework.

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Section: Resultsmentioning

confidence: 99%

Pressure-induced superconductivity in Sc to74GPa

Hamlin

Schilling

2007

Phys. Rev. B

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“…3b) [25,26]. Whereas no T c (P ) data is available across the I→II boundary, T c is seen to drop sharply at the II→III boundary and then rise slowly as the pressure is increased further.…”

Section: Sc Metalmentioning

confidence: 99%

“…Whereas in Lu T c increases monotonically with pressure to 12.4 K at 174 GPa, in Sc T c increases rapidly with pressure, reaching a maximum value of 19.6 K at 107 GPa in the Sc-II phase. If the pressure is increased further, Sc-II transforms to Sc-III [25,26] whereupon T c drops to 8.31 K at 111 GPa. Sc possesses with 19.6 K the second highest value of T c of any elemental superconductor.…”

Section: Introductionmentioning

confidence: 99%

Comparison of the pressure dependences ofTcin the trivalentd-electron superconductors Sc, Y, La, and Lu up to megabar pressures

2008

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Whereas dhcp La superconducts at ambient pressure with T c ≃ 5 K, the other trivalent d-electron metals Sc, Y, and Lu only superconduct if high pressures are applied. Earlier measurements of the pressure dependence of T c for Sc and Lu metal are here extended to much higher pressures. Whereas T c for Lu increases monotonically with pressure to 12.4 K at 174 GPa (1.74 Mbar). T c for Sc reaches 19.6 K at 107 GPa, the 2nd highest value observed for any elemental superconductor. At higher pressures a phase transition occurs whereupon T c drops to 8.31 K at 111 GPa. The T c (P ) dependences for Sc and Lu are compared to those of Y and La. An interesting correlation is pointed out between the value of T c and the fractional free volume available to the conduction electrons outside the ion cores, a quantity which is directly related to the number of d electrons in the conduction band.

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“…But the magnitude of the effect seems improbably large, noting that the spacing of 1.957 Å at 101 GPa is even smaller than the closest contact distance of 2.052͑2͒ Å in Sc-V at the very much higher pressure of 242 GPa. 10 In this paper we propose a different incommensurate composite solution. It has the same host structure but a guest component that has a larger spacing along the c axis and is C-face-centered rather than body-centered, isostructural with Sr-V rather than Bi-III.…”

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confidence: 99%

Different incommensurate composite crystal structure for Sc-II

et al. 2006

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The long uncertain crystal structure of the high-pressure phase of scandium, Sc-II, is found to have an incommensurate composite structure comprising a body-centered host structure and a C-face-centered guest structure. At 23 GPa, the shortest distance between guest atoms is ϳ2.7 Å, comparable to the average hosthost distance of 2.8 Å. This differs from the structure proposed recently ͓H. Fujihisa et al., Phys. Rev. B 72, 132103 ͑2005͔͒ which has a body-centered guest structure, with anomalously short guest-guest distances.The development of advanced angle-dispersive powder and single-crystal diffraction techniques has led to the discovery of a number of complex incommensurate crystal structures in the elements at high pressures. 1 The group II and V elements, Ba and Sr, 2,3 and As, Sb, and Bi, 4-6 have high-pressure phases comprising an 8-atom body-centered host structure and linear chains of guest atoms lying in channels, along the c axis, through the host framework ͓Fig. 1͑a͔͒. And these guest chains form a simple body-centered ͓Fig. 1͑a͔͒ or C-face-centered structure which is incommensurate with the host along their common c axis. The group I elements K and Rb ͑Refs. 1, 7, and 8͒ also have a composite host-guest structure at high pressure, but with a 16-atom host structure ͓Fig. 1͑b͔͒.Recently, Fujihisa et al. 9 have reported that scandium, the first of the 3d transition metals, also possesses an incommensurate composite structure above 22 GPa ͑Sc-II͒, with the same body-centered host and guest structures as Bi-III and Sb-II ͓as in Fig. 1͑a͔͒. This is an important result in revealing the stability of host-guest composite structures in another group of elements with a quite different electronic configuration, and it suggests that still more such phases may be found. However, this solution has an anomalously short guest-guest distance along the chains, as Fujihisa et al. acknowledge, 9 although the fit to the powder diffraction profiles is good. At 23 GPa, the guest-guest distance ͑d 4 in Ref.9͒ is only 2.285 Å, some 18% shorter than the average hosthost contact distance of 2.79 Å ͑d 1 and d 2 in Ref. 9͒. And this difference increases to 21% at 101 GPa, where the guest-guest spacing is only 1.957 Å. This is quite unlike all the other composite structures found to date ͑Ba-IV, Sr-V, K-III, Rb-IV, As-III, Sb-II, Sb-IV, and Bi-III͒, in which the spacing of the guest atoms differs from the host-host contact distances by no more than 2%. Fujihisa et al. suggest that the short spacing might arise from a difference in the electronic structure of the host and guest atoms. But the magnitude of the effect seems improbably large, noting that the spacing of 1.957 Å at 101 GPa is even smaller than the closest contact distance of 2.052͑2͒ Å in Sc-V at the very much higher pressure of 242 GPa. 10 In this paper we propose a different incommensurate composite solution. It has the same host structure but a guest component that has a larger spacing along the c axis and is C-face-centered rather than body-centered, isostructural w...

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New Helical Chain Structure for Scandium at 240 GPa

Cited by 65 publications

References 20 publications

Pressure-induced superconductivity in Sc to74GPa

Pressure-induced superconductivity in Sc to74GPa

Comparison of the pressure dependences ofTcin the trivalentd-electron superconductors Sc, Y, La, and Lu up to megabar pressures

Different incommensurate composite crystal structure for Sc-II

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