Melting of Dense Sodium

Gregoryanz, Eugene; Degtyareva, Olga; Somayazulu, Maddury; Hemley, Russell J.; Mao, Ho‐kwang

doi:10.1103/physrevlett.94.185502

Cited by 207 publications

(180 citation statements)

References 44 publications

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“…An example is the complexity of structure revealed at HP. Contrary to the conventional understanding that the crystal structures at HP becomes increasingly simple like arrays of closely packed balls, HP increases the interaction of the inner electrons, and atoms may become irregularly-shaped and non-spherical, resulting in very complicated crystal structures and very large unit cells [345,346] (Fig. 19).…”

Section: Hp Crystallographymentioning

confidence: 89%

High-pressure studies with x-rays using diamond anvil cells

2016

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Pressure profoundly alters all states of matter. The symbiotic development of ultrahighpressure diamond anvil cells, to compress samples to sustainable multi-megabar pressures; and synchrotron x-ray techniques, to probe materials' properties in situ, has enabled the exploration of rich high-pressure (HP) science. In this article, we first introduce the essential concept of diamond anvil cell technology, together with recent developments and its integration with other extreme environments. We then provide an overview of the latest developments in HP synchrotron techniques, their applications, and current problems, followed by a discussion of HP scientific studies using x-rays in the key multidisciplinary fields. These HP studies include: HP x-ray emission spectroscopy, which provides information on the filled electronic states of HP samples; HP x-ray Raman spectroscopy, which probes the HP chemical bonding changes of light elements; HP electronic inelastic x-ray scattering spectroscopy, which accesses high energy electronic phenomena, including electronic band structure, Fermi surface, excitons, plasmons, and their dispersions; HP resonant inelastic x-ray scattering spectroscopy, which probes shallow core excitations, multiplet structures, and spin-resolved electronic structure; HP nuclear resonant x-ray spectroscopy, which provides phonon densities of state and time-resolved Mössbauer information; HP x-ray imaging, which provides information on hierarchical structures, dynamic processes, and internal strains; HP x-ray diffraction, which determines the fundamental structures and densities of single-crystal, polycrystalline, nanocrystalline, and non-crystalline materials; and HP radial x-ray diffraction, which yields deviatoric, elastic and rheological information. Integrating these tools with hydrostatic or uniaxial pressure media, laser and resistive heating, and cryogenic cooling, has enabled investigations of the structural, vibrational, electronic, and magnetic properties of materials over a wide range of pressure-temperature conditions.

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Section: Hp Crystallographymentioning

confidence: 89%

High-pressure studies with x-rays using diamond anvil cells

2016

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“…Between 2002 and 2008, a number of phase transitions of sodium at pressures up to 160 GPa were observed [42][43][44]. In 2009, in three letters to Nature in the same issue [45][46][47], it was shown that both lithium and sodium lose their metallic character under pressure.…”

Section: From Solvated Electrons To Electridesmentioning

confidence: 99%

The alkali metals: 200 years of surprises

Dye

2015

Phil. Trans. R. Soc. A.

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Microscopic Origins of the Anomalous Melting Behavior of Sodium under High Pressure

et al. 2012

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Recent experiments have shown that sodium, a prototype simple metal at ambient conditions, exhibits unexpected complexity under high pressure [1][2][3][4] . One of the most puzzling phenomena in the behaviour of dense sodium is the pressureinduced drop in its melting temperature, which extends from 1000 K at ∼30 GPa to as low as room temperature at ∼120 GPa 1 . Despite significant theoretical effort to understand the anomalous melting 5-10 its origins have remained unclear. In this work, we reconstruct the sodium phase diagram using an ab-initio-quality neural-network potential 11,12 . We demonstrate that the reentrant behaviour results from the screening of interionic interactions by conduction electrons, which at high pressure induces a softening in the shortrange repulsion. It is expected that such an effect plays an important role in governing the behaviour of a wide range of metals and alloys.At ambient conditions, sodium crystallizes in the bodycentered cubic (bcc) structure, which transforms to the face-centered cubic (fcc) phase upon compression to 65 GPa 13 . At 105 GPa, the fcc phase undergoes a transformation to the cI16 phase -a distorted variant of the bcc structure 2 . Further compression results in the formation of a large variety of complex phases 3,4 , the existence of which is quite intriguing. However, the focus of this work is one of the most striking features of the sodium phase diagram -the anomalous melting curve. Diffraction measurements have revealed a maximum in melting temperature around 1000 K at ∼30 GPa followed by a pressure-induced drop, which extends to nearly room temperature at ∼120 GPa 1 and spans the regions of stability of three solid phases (Fig. 1a). This anomaly implies that in this range the liquid is denser than the solid.Although previous ab initio studies 5-10 have reproduced the reentrant melting behaviour of sodium the physical origin of this anomaly still remains unclear. The hypothesis of structural and electronic transitions in liquid sodium proposed in one of the studies 6 has not been confirmed by other authors 5 . The discrepancy between these simulation results has been attributed to a different treatment of the semicore states 8 .It is important to point out that due to the high computational cost of ab initio MD all simulations so far re- ported 5-8 have used small simulation cells and estimated melting temperatures (T m ) by heating the solid phase until it melts. In such simulations, the absence of nucleation centers and fast heating schedules delay melting relative to the thermodynamic coexistence point and, therefore, only an upper bound on T m can be obtained. A proper reconstruction of the melting curve requires comparing the free energies of the liquid and solid phases and involves long (∼10 ns) MD simulations on large systems (∼ 10 3 atoms). Performing such simulations with direct ab initio methods is computationally too expensive at present.

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Melting of Dense Sodium

Cited by 207 publications

References 44 publications

High-pressure studies with x-rays using diamond anvil cells

High-pressure studies with x-rays using diamond anvil cells

The alkali metals: 200 years of surprises

Microscopic Origins of the Anomalous Melting Behavior of Sodium under High Pressure

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