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Nonexistence of the s−f volume-collapse transition in solid gadolinium at pressure

DOI: 10.1103/PhysRevB.104.144108 DOI Help

Authors: Qingchen Li (University of Edinburgh) , Hossein Ehteshami (University of Edinburgh) , Keith Munro (University of Edinburgh) , Miriam Marqués (University of Edinburgh) , Malcolm Mcmahon (University of Edinburgh) , Simon G. Macleod (University of Edinburgh; AWE) , Graeme J. Ackland (University of Edinburgh)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Physical Review B , VOL 104

State: Published (Approved)
Published: October 2021
Diamond Proposal Number(s): 11768

Abstract: Gadolinium has long been believed to undergo a high-pressure phase transition with a volume collapse around 5%. Theoretical explanations have focused on the idea of electrons transferring from the extended s -orbital to the compact f -orbital. However, experimental measurement has been unable to detect any associated change in the magnetic properties of the f -electrons [Fabbris et al., Phys. Rev. B 88, 245103 (2013)]. Here we resolve this discrepancy by showing that there is no significant volume collapse, beyond what is typical in high-pressure phase transformations. We present density functional theory calculations of solid gadolinium under high pressure using a range of methods, and revisit the experimental situation using x-ray diffraction (XRD). The standard lanthanide pressure-transformation sequence involving different stackings of close-packed planes h c p → 9 R → dhcp → fcc → d − fcc is reproduced. The so-called “volume-collapsed” high-pressure phase is shown to be an unusual stacking of close-packed planes, with Fddd symmetry and a density change of less than 2%. The distorted fcc (d-fcc) structure is revealed to arise as a consequence of antiferromagnetism. The theoretical results are shown to be remarkably robust to various treatments of the f -electrons. The key result is that there is no XRD evidence for volume collapse in gadolinium. The sequence of phase transitions is well described by standard density functional theory. There is no need for special treatment of the f -electrons or evidence of f -electron bonding. Noting that in previous spectroscopic evidence there is no change in the f -electrons we conclude that high-pressure gadolinium has no complicated f -electron physics such as Mott-Hubbard, Kondo, or valence transitions.

Journal Keywords: Crystal binding; Density of states; Electronic structure; First order phase transitions; Magnetic phase transitions; Phase diagrams

Diamond Keywords: Antiferromagnetism

Subject Areas: Materials, Physics

Instruments: I15-Extreme Conditions

Added On: 20/10/2021 09:25

Discipline Tags:

Materials Science Quantum Materials Physics Hard condensed matter - structures Magnetism

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