Large Structural Modulations in Incommensurate Te-III and Se-IV

Hejny, Clivia; McMahon, M. I.

doi:10.1103/physrevlett.91.215502

Cited by 98 publications

(131 citation statements)

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“…For instance, modulated structures are often found in the highpressure phases of elements. Lattice modulations have been found in group Vb elements, including As, Sb, and Bi [1,2], and the group VIb elements S [3], Se [4], and Te [5]. Modulated structures have also been reported in the halogens I [6] and Br [7].…”

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confidence: 77%

Determining the Structure of Phosphorus in Phase IV

et al. 2006

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We explore the unknown structure of phosphorus in phase IV (P-IV phase) based on first-principles calculations using the metadynamics simulation method. Starting from the simple cubic structure, we find a new modulated structure of the monoclinic lattice. The modulation is crucial to the stability of the structure. Through refining the structure further by changing the modulation period, we find the structure whose x-ray powder diffraction pattern is in best agreement with the experimental pattern. We expect that the modulation period of the structure in the P-IV phase is very close to that found in this study and probably incommensurate. DOI: 10.1103/PhysRevLett.96.095502 PACS numbers: 61.50.Ah, 62.50.+p, 64.70.Kb Recent progress in high-pressure physics has enhanced our recognition of a wide variety of crystal structures. Development of high-pressure techniques has also enabled the identification of structures that are stabilized only in a narrow pressure range. Interesting structures were found unexpectedly through high-pressure experiments. For instance, modulated structures are often found in the highpressure phases of elements. Lattice modulations have been found in group Vb elements, including As, Sb, and Bi Scarcity of experimental ultrahigh-pressure data restricts high-pressure studies. Thus, researchers often encounter difficulties in the identification of a crystal structure on the basis of experimental data alone. A theoretical approach provides additional information on the same problem. First-principles theory for determining crystal structures is believed to be sufficiently accurate. However, the limitations of computational resources sometimes impede full structure searches.We will focus on the case of phase IV of the phosphorus (P-IV) phase. Observation of the P-IV phase was first reported by Akahama et al. [8] in 1999. In the sequence of pressure-induced transformations, the simple cubic (sc) phase (P-III) appears at 10 GPa at low temperature. Akahama et al. [8] reported the appearance of a simple hexagonal (sh) phase, i.e., the P-V phase, which stabilizes above 137 GPa, and an intermediate phase, i.e., the P-IV phase, between sc and sh on the basis of x-ray diffraction data. At even higher pressures, the bcc structure (P-VI) has been theoretically predicted [9] and later identified in an experiment at 262 GPa [10]. The structure of phase IV, however, has not been identified experimentally. Ordinary Rietveld analysis based on a knowledge of the monoclinic symmetry alone has not been successful, presumably owing to the complexity of the lattice. Thus, we must guess the crystal structure or a pseudocrystal.Several structures have been tested as candidate structures for P-IV. Ahuja considered a structure of space group Imma [11]. Ehlers and Christensen studied relative stability of the Ba-IV structure against sc and sh in the pressure range from 100 to 200 GPa [12]. The Ba-IV structure is a kind of modulated structure. Despite these extensive studies, the structure of P-IV remains unidentifi...

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confidence: 77%

Determining the Structure of Phosphorus in Phase IV

et al. 2006

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“…1. The Bragg reflections can be indexed using four Miller indices (h,k,l,m) according to H = ha * + kb * + lc * + mq, where a * ,b * ,c * define the reciprocal lattice of the mC4 average structure and q is the modulation vector, according to the 4D superspace formalism [18] as described in our previous work [7,19]. Only first-order (m = ±1) satellite reflections were observed.…”

Section: A Transition To Eu-vmentioning

confidence: 99%

Incommensurate-to-incommensurate phase transition in Eu metal at high pressures

et al. 2014

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High pressure x-ray powder-diffraction experiments were performed on europium metal up to ∼70 GPa. Above 38 GPa, europium transforms from the incommensurately modulated Eu-IV phase to a second phase with an incommensurately modulated crystal structure, Eu-V. This is a previously unseen incommensurately modulated to incommensurately modulated transition in the elements at high pressure. High-pressure high-temperature experiments were also performed up to 449 K in order to make an initial estimate of the positions of the phase boundaries of the incommensurate phases.

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“…Incommensurate modulated structure can be viewed as a basic structure with the atoms displaced by a modulation wave, which is incommensurate with the basic unit cells. Examples of these types of structures include Te, Se, S, I, and Br [349,350,[358][359][360]. Modulated layer structures consist of various different stacking sequences of similar 8-atom and 10 atom layers at HP, such as in Li [361], Cs [362], Rb [363], and Ga [364].…”

Section: Hp Crystallographymentioning

confidence: 99%

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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Large Structural Modulations in Incommensurate Te-III and Se-IV

Cited by 98 publications

References 24 publications

Determining the Structure of Phosphorus in Phase IV

Determining the Structure of Phosphorus in Phase IV

Incommensurate-to-incommensurate phase transition in Eu metal at high pressures

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

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