High-pressure transformations in simple melts

Бражкин, В. В.; Попова, С. В.; Волошин, Р. Н.

doi:10.1080/08957959708240477

Cited by 153 publications

(87 citation statements)

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“…Above 2.4 GPa, the melting curve of Bi-V exhibits a steep positive slope. An electrical resistivity and thermobaric study (12) claims that molten Bi has several liquid phases up to 6 GPa. However, no structural studies have been reported to confirm these phases.…”

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confidence: 99%

Deep melting reveals liquid structural memory and anomalous ferromagnetism in bismuth

Shu

Wang

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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As an archetypal semimetal with complex and anisotropic Fermi surface and unusual electric properties (e.g., high electrical resistance, large magnetoresistance, and giant Hall effect), bismuth (Bi) has played a critical role in metal physics. In general, Bi displays diamagnetism with a high volumetric susceptibility (∼10 −4 ). Here, we report unusual ferromagnetism in bulk Bi samples recovered from a molten state at pressures of 1.4-2.5 GPa and temperatures above ∼1,250 K. The ferromagnetism is associated with a surprising structural memory effect in the molten state. On heating, low-temperature Bi liquid (L) transforms to a more randomly disordered high-temperature liquid (L ) around 1,250 K. By cooling from above 1,250 K, certain structural characteristics of liquid L are preserved in L. Bi clusters with characteristics of the liquid L motifs are further preserved through solidification into the Bi-II phase across the pressure-independent melting curve, which may be responsible for the observed ferromagnetism.bismuth | high pressure | ferromagnetism | melt structure B ismuth (Bi) has played important roles in metal and condensed matter physics. The extremely low carrier density of Bi allows quantum limits of the Landau level to be studied under high magnetic field (1) and quantum size effects to be observed at ∼100-nm length scale (2). At ambient condition, Bi is known to crystallize in the rhombohedral A-7 type structure (space group R-3m, D 5 3d ), with the primitive unit cell containing two atoms at positions (u, u, u) and (−u, −u, −u). Each atom has three equidistant nearest neighbors tightly bonded at a distance of ∼3.062Å (3). The Bi4 motifs form puckered bilayers ( Fig. S1A) with a thickness of 1.59Å stacked along the rhombohedral [111] direction. The distance between adjacent bilayers is 2.35Å (4), slightly smaller than the next nearest distance of 3.512Å (5). Each atom's next nearest neighbors are in the adjacent bilayers, and the bonding within each bilayer is much stronger than the interbilayer bonding. As such, Bi exhibits rather complex interatomic binding, with coexisting covalent (within the bilayers), metallic, and weaker van der Waals-like (between bilayers) bonding (4).The phase diagram of Bi is rich and complex ( Fig. 1). At ambient pressure, Bi melts at 544 K (6) with a liquid-liquid transition at 1,010 K (7). With increasing pressure, Bi undergoes structural transitions in both solid and liquid states. The A-7 structured Bi-I phase transforms successively into the monoclinic (Bi-II), incommensurate host-guest (Bi-III), and body-centered cubic (Bi-V) phases (8-10) with increasing pressure to ∼6 GPa. On pressure release, these high-pressure metallic crystalline phases are unstable and revert to the Bi-I phase. Below ∼1.6 GPa, the melting temperature of Bi-I decreases with increasing pressure, a behavior similar to that of ice. Between 1.6 and 2.4 GPa (11), the solid just below melting is the Bi-II phase, which has a similar bilayer structure to that of Bi-I, except that the distance betwe...

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confidence: 99%

Deep melting reveals liquid structural memory and anomalous ferromagnetism in bismuth

Shu

Wang

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…For example, the two-liquid models [4] assume that liquids at high pressure are a mixture of two liquid phases whose relative concentration depends on external parameters. Other explanations for the liquid-liquid phase transition assume an anisotropic potential [2,[11][12][13].…”

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Generic mechanism for generating a liquid–liquid phase transition

Franzese

Malescio

Skibinsky

et al. 2001

Nature

381

326

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Recent experimental results [1] indicate that phosphorus, a single-component system, can have two liquid phases: a high-density liquid (HDL) and a low-density liquid (LDL) phase. A firstorder transition between two liquids of different densities [2] is consistent with experimental data for a variety of materials [3,4], including singlecomponent systems such as water [5][6][7][8], silica [9] and carbon [10]. Molecular dynamics simulations of very specific models for supercooled water [2,11], liquid carbon [12] and supercooled silica [13], predict a LDL-HDL critical point, but a coherent and general interpretation of the LDL-HDL transition is lacking. Here we show that the presence of a LDL and a HDL can be directly related to an interaction potential with an attractive part and two characteristic short-range repulsive distances. This kind of interaction is common to other single-component materials in the liquid state (in particular liquid metals [14-21,2]), and such potentials are often used to decribe systems that exhibit a density anomaly [2]. However, our results show that the LDL and HDL phases can occur in systems with no density anomaly. Our results therefore present an experimental challenge to uncover a liquid-liquid transition in systems like liquid metals, regardless of the presence of the density anomaly.Several explanations have been developed to understand the liquid-liquid phase transition. For example, the two-liquid models [4] assume that liquids at high pressure are a mixture of two liquid phases whose relative concentration depends on external parameters. Other explanations for the liquid-liquid phase transition assume an anisotropic potential [2,[11][12][13]. Here we shall see that liquid-liquid phase transition phenomena can arise solely from an isotropic pair interaction potential with two characteristic lengths.For molecular liquid phosphorus P 4 (as for water), a tetrahedral open structure is preferred at low pressures P and low temperatures T , while a denser structure is favored at high P and high T [1,6,8]. The existence of these two structures with different densities suggests a pair interaction with two characteristic distances. The first distance can be associated with the hard-core exclusion between two particles and the second distance with a weak repulsion (soft-core), which can be overcome at large pressure. Here we will use a generic three dimensional (3D) model composed of particles interacting via an isotropic soft-core pair potential. Such isotropic potentials can be regarded as resulting from an average over the angular part of more realistic potentials, and are often used as a first approximation to understand the qualitative behavior of real systems [14][15][16][17][18][19][20][21][22]2]. For Ce and Cs, Stell and Hemmer proposed a potential with nearest-neighbor repulsion and a weak long-range attraction [15]. By means of an exact analysis in 1D, they found two critical points, with the high-density critical point interpreted as a solid-solid transition. Then analytic calc...

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