Superconducting Open-Framework Allotrope of Silicon at Ambient Pressure (original) (raw)
Abstract
Diamond Si is a semiconductor with an indirect band gap that is the basis of modern semiconductor technology. Although many metastable forms of Si were observed using diamond anvil cells for compression and chemical precursors for synthesis, no metallic phase at ambient conditions has been reported thus far. Here we report the prediction of pure metallic Si allotropes with open channels at ambient pressure, unlike a cubic diamond structure in covalent bonding networks. The metallic phase termed P6/m−Si6 can be obtained by removing Na after pressure release from a novel Na-Si clathrate called P6/m−NaSi6, which is predicted through first-principles study at high pressure. We identify that both P6/m−NaSi6 and P6/m−Si6 are stable and superconducting with the critical temperatures of about 13 and 12 K at ambient pressure, respectively. The prediction of new Na-Si and Si clathrate structures presents the possibility of exploring new exotic allotropes useful for Si-based devices.
- Received 16 August 2017
- Corrected 13 April 2018
DOI:https://doi.org/10.1103/PhysRevLett.120.157001
© 2018 American Physical Society
Research Areas
Physical Systems
Techniques
Condensed Matter, Materials & Applied Physics
Corrections
13 April 2018
Correction: The third sentence in the caption to Fig. 2 was inconsistent with the image and has been replaced. The author list in Ref. [30] contained an error and was corrected.
Click to Expand
Authors & Affiliations
Ha-Jun Sung1, W. H. Han1, In-Ho Lee2, and K. J. Chang1,*
- 1Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea
- 2Korea Research Institute of Standards and Science, Daejeon 34113, Korea
- *Corresponding author. kjchang@kaist.ac.kr
Click to Expand
Article Text (Subscription Required)
Click to Expand
Supplemental Material (Subscription Required)
Click to Expand
References (Subscription Required)
Click to Expand
Authorization Required
×
Images
Figure 1
Formation enthalpies of stable and metastable configurations for Na1−xSix with various composition ratios at pressures of 10 GPa (top) and 20 GPa (bottom). The configurations on the convex hull are marked by solid symbols and connected by red lines.
Reuse & Permissions
Figure 2
(a) Top and side views of the atomic structures of P6/m−NaSi6 (left) and P6/m−Si6 (right) clathrates. In P6/m−NaSi6, the open channels filled with Na atoms are embedded in the metallic bonding networks of Si atoms that are exactly the same as that of a simple hexagonal lattice except for the open channels. The green and yellow spheres represent Na and Si atoms, respectively. (b) Relative enthalpies (ΔH) of various clathrate structures with respect to a mixture of Zintl and CD-Si as a function of pressure.
Reuse & Permissions
Figure 3
(a) Phonon spectra, phonon densities of states (PDOS in arb. unit), Eliashberg spectral functions α2F(ω), and electron-phonon couplings λ(ω) for P6/m−NaSi6 (top) and P6/m−Si6 (bottom) at 15 GPa. The magnitude of λ(ω) is indicated by the thickness of the red curves. (b) Band structures and electronic densities of states (DOS in arb. unit) of P6/m−NaSi6 (top) and P6/m−Si6 (bottom) at 15 GPa, with the Fermi level set to zero.
Reuse & Permissions
Figure 4
(a) Pressure dependences of Tc and λ for P6/m−NaSi6 and P6/m−Si6. (b) Pressure variation of the low-frequency modes of P6/m−Si6 along the Γ−A−L line in the BZ. The balls represent the Si atoms around the open channels and the arrows stand for the displacements of the TA mode at the A point. (c) Energy vs volume curves of various Si phases.
Reuse & Permissions
×