| 1. |
- Dubrovinsky, L., et al.
(author)
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Noblest of all metals is structurally unstable at high pressure
- 2007
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 98:4
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Journal article (peer-reviewed)abstract
- In a series of experiments in externally electrically heated diamond anvil cells we demonstrate that at pressures above similar to 240 GPa gold adopts a hexagonal-close-packed structure. Ab initio calculations predict that at pressures about 250 GPa different stacking sequences of close-packed atomic layers in gold become virtually degenerate in energy, strongly supporting the experimental observations.
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| 2. |
- Ahuja, Rajeev, et al.
(author)
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High-pressure structural transitions in Cm and Am0.5Cm0.5 binary alloy
- 2006
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In: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 26:4, s. 377-381
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Journal article (peer-reviewed)abstract
- The high-pressure behaviour of Cm and Am0.5Cm0.5 binary alloy is investigated theoretically using ab initio electronic structure methods. Our calculations reproduce the structural phase transitions, which are observed in recent experiment performed by Heathman et al. [S. Heathman, R.G. Haire, I Le Bihan et al., Science 309 110 (2005)] and Lindbaum et al. [A. Lindbaum, S. Heathman, T. Le Bihan et al., J. Phys: Condens. Matter 15 S2297 (2003)]. Calculated transition pressures are in reasonable agreement with the experimental values. Calculations performed for an antiferromagnetic state are essential to reproduce the stability of Cm-III phase.
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| 3. |
- Heathman, S., et al.
(author)
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The unique high-pressure behavior of curiurn probed further using alloys
- 2007
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In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 444, s. 138-141
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Journal article (peer-reviewed)abstract
- The changing role of the 5f electrons across the actinide series has been of prime interest for many years. The remarkable behavior of americium's 5f electrons under pressure was determined experimentally a few years ago and it precipitated a strong interest in the heavy element community. Theoretical treatments of americium's behavior under pressure followed and continue today. Experimental and theoretical findings regarding curium's behavior under pressure have shown that the pressure behavior of curium was not a mirror image of that for americium. Rather, one of the five crystallographic phases observed with curium (versus four for americium) was a unique monoclinic structure whose existence is due to a spin stabilization effect by curium's 5f(7) electronic configuration and its half-filled 5f-shell. We review briefly the behavior of pure curium under pressure but focus on the pressure behaviors of three curium alloys with the intent of comparing them with pure curium. An important experimental finding confirmed by theoretical computations, is that dilution of curium with its near neighbors is sufficient to prevent the formation of the unique C2/c phase that appears in pure Cm metal under pressure. As this unique C2/c phase is very sensitive to having a 5f7 configuration to maximize the magnetic spin polarization, dilution of this state with adjacent actinide neighbors reduces its stability.
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| 4. |
- Johansson, Börje, et al.
(author)
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Cerium; Crystal Structure and Position in The Periodic Table
- 2014
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 6398-
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Journal article (peer-reviewed)abstract
- The properties of the cerium metal have intrigued physicists and chemists for many decades. In particular a lot of attention has been directed towards its high pressure behavior, where an isostructural volume collapse (gamma phase -> alpha phase) has been observed. Two main models of the electronic aspect of this transformation have been proposed; one where the 4f electron undergoes a change from being localized into an itinerant metallic state, and one where the focus is on the interaction between the 4f electron and the conduction electrons, often referred to as the Kondo volume collapse model. However, over the years it has been repeatedly questioned whether the cerium collapse really is isostructural. Most recently, detailed experiments have been able to remove this worrisome uncertainty. Therefore the isostructural aspect of the a-c transition has now to be seriously addressed in the theoretical modeling, something which has been very much neglected. A study of this fundamental characteristic of the cerium volume collapse is made in present paper and we show that the localized reversible arrow delocalized 4f electron picture provides an adequate description of this unique behavior. This agreement makes it possible to suggest that an appropriate crossroad position for cerium in The Periodic Table.
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| 5. |
- Luo, Wei, et al.
(author)
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Dynamical stability of body center cubic iron at the Earth's core conditions
- 2010
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 107:22, s. 9962-9964
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Journal article (peer-reviewed)abstract
- Here, using self-consistent ab initio lattice dynamical calculations that go beyond the quasiharmonic approximation, we show that the high-pressure high-temperature bcc-Fe phase is dynamically stable. In this treatment the temperature-dependent phonon spectra are derived by exciting all the lattice vibrations, in which the phonon-phonon interactions are considered. The high-pressure and high-temperature bcc-Fe phase shows standard bcc-type phonon dispersion curves except for the transverse branch, which is overdamped along the high symmetry direction Gamma-N, at temperatures below 4,500 K. When lowering the temperature down to a critical value T-C, the lattice instability of the bcc structure is reached. The pressure dependence of this critical temperature is studied at conditions relevant for the Earth's core.
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| 6. |
- Shi, H., et al.
(author)
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Electronic and elastic properties of CaF2 under high pressure from ab initio calculations
- 2009
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 21:41
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Journal article (peer-reviewed)abstract
- Calcium fluoride CaF2 has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). Our results demonstrate that the sequence of the pressure-induced structural transition of CaF2 is the fluorite structure (Fm (3) over barm), the orthorhombic cotunnite-type structure (Pnma), and the hexagonal Ni2In-type structure (P6(3)/mmc). The two transitions occur at pressures of 8 GPa and 105 GPa, accompanied by volume collapses of 8.4% and 1.2%, respectively. The energy band gap increases with pressure in the (Fm (3) over barm) and the forepart of Pnma phases. However, on increasing the pressure beyond 60 GPa, the gap decreases, which is due to the fluorine p(z)-states shifting toward the Fermi energy. In addition, the elastic properties versus pressure are also discussed. Our calculated elastic constants for the cubic phase at ambient pressure are in agreement with the experimental values. The stress-strain coefficient calculations show that shear transformations in the Pnma phase are more difficult than in the cubic phase and the compressibility along the c(h) (or a(o)) direction for the orthorhombic phase is stronger than that in the hexagonal crystal.
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| 7. |
- Shi, H., et al.
(author)
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First-principles calculations of the electronic structure and pressure-induced magnetic transition in siderite FeCO3
- 2008
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:15
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Journal article (peer-reviewed)abstract
- Rhombohedral siderite FeCO3 has been studied by using density-functional theory with the generalized gradient approximation (GGA). In order to take into account the strong on-site Coulomb interaction U present in FeCO3, we also performed the GGA+U calculations. We observe a pressure-induced magnetic transition (high spin -> low spin) at pressures of 15 and 28 GPa, which are underestimated with respect to the experiment, for the GGA and GGA+U calculations, respectively. This phase transition was with a volume collapse of 10% around, also accompanied by increases in bulk modulus, Young's modulus and sound velocity. The electronic density of states and charge-density calculations revealed that the magnetic transition was due to the pressure-induced Fe 3d electron delocalization.
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| 8. |
- Springell, R., et al.
(author)
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Elemental engineering : Epitaxial uranium thin films
- 2008
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:19
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Journal article (peer-reviewed)abstract
- Epitaxial films of the well-known alpha (orthorhombic) structure and an unusual hcp form of uranium have been grown on Nb and Gd buffers, respectively, by sputtering techniques. In a 5000 A film of alpha-U a charge-density wave has been observed, and its properties are different from those found in the bulk. The 500 A hcp-U film has a c/a ratio of 1.90(1), which is unusually large for the hcp structure. Theoretical calculations show that this hcp form is metastable and predict that it orders magnetically.
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| 9. |
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| 10. |
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