Structure and relaxation in liquid and amorphous selenium

Caprion, D.; Schober, H. R.

doi:10.1103/physrevb.62.3709

Cited by 73 publications

(71 citation statements)

References 55 publications

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“…Amorphous Se has branched chains that include rings of different bond lengths, and both chain and ring-type local configurations should coexist (39,40). Theoretical calculations predict that a volume expansion occurs in the initial stages of formation of crystal nuclei (41).…”

Section: Resultsmentioning

confidence: 99%

Anomalous high-pressure behavior of amorphous selenium from synchrotron x-ray diffraction and microtomography

Liu

Wang

Xiao

et al. 2008

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

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The high-pressure behavior of amorphous selenium has been investigated with time-resolved diamond anvil cell synchrotron x-ray diffraction and computed microtomography techniques. A two-step dynamic crystallization process is observed in which the monoclinic phase crystallized from the amorphous selenium and gradually converted to the trigonal phase, thereby explaining previously observed anomalous changes in electrical conductivity of the material under pressure. The crystallization of this elemental system involves local topological fluctuations and results in an unusual pressure-induced volume expansion. The metastability of the phases involved in the transition accounts for this phenomenon. The results demonstrate the use of pressure to control and directly monitor the relative densities and energetics of phases to create new phases from highly metastable states. The microtomographic technique developed here represents a method for determination of the equations of state of amorphous materials at extreme pressures and temperatures.crystallization ͉ volume expansion ͉ equation of state ͉ phase transition ͉ metastability T he behavior of amorphous materials under pressure is a problem of great current interest. Unusual behavior, such as pressure-induced amorphization of crystalline forms, pressureinduced polyamorphism low-to high-density forms of insulating and metallic glasses, and the dynamics of pressure-induced crystallization are reported but not fully understood (1-10). The nature of the behavior of amorphous solids under pressure is complicated by their metastability and the possibility of irreversible relaxation of their properties and structure (11). Amorphous selenium (a-Se) is a model system for examining pressure effects in amorphous materials because of the wide range of structure and bonding properties expected based on the behavior of the crystalline polymorphs of the element. In experiments designed to understand the high-pressure behavior of a-Se, we have discovered an unexpected pressure-induced dynamic crystallization process associated with a volume expansion in the material. The origin of this unusual phenomenon is examined by using a microtomography technique that allows direct measurement of the equation of state (EOS) of the amorphous phase.Recent efforts to characterize the structural evolution of group VI elements under pressure, such as novel dense chain structures in sulfur and selenium (12), and the alternating phase transition sequence in sulfur at high pressure and temperature (13), have led to a new level of understanding of the phase diagrams and structures of these materials. Under pressure, selenium exhibits a complex polymorphism, and the diversity of phases and transition sequences observed depend strongly on the starting material (12,(14)(15)(16)(17)(18)(19)(20)(21). First studied by x-ray diffraction (XRD) in 1972 (22), a-Se was found to crystallize in a trigonal structure (t-Se) at Ϸ10 GPa (23-27). However, its electrical resistance was clearly different from pure t-Se i...

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Section: Resultsmentioning

confidence: 99%

Anomalous high-pressure behavior of amorphous selenium from synchrotron x-ray diffraction and microtomography

Liu

Wang

Xiao

et al. 2008

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

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“…7), which grows with increasing rod lengthin analogy to decreasing temperature in supercooled liquids or increasing density in colloids. As also observed in these latter systems [11,12,13,14,15,16,17,18], the region around the maximum of the peak corresponds to the time interval corresponding to the end of the caging and the beginning of the long-time diffusive regime. Thus, the breaking of the cage leads to a finite probability of jumps much longer that the size of the cage, resulting in a strongly heterogeneous dynamics at that intermediate time and spatial scale, which is reflected by a peak in the non-Gaussian parameter.…”

Section: Non-gaussian Effectsmentioning

confidence: 84%

“…For simplicity simulations have been done in two dimensions, reducing the degrees of freedom to the center-of-mass position and the orientation of the rod axis. As in the case of supercooled liquids [11,12,13,14,15] or dense colloidal systems [16,17,18], one observes at intermediate times a caging regime for the rod center-of-mass motion, which is due to the steric hindrance produced by the presence of the neighboring obstacles.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast to this, for long rods a crossover regime between both limits, showing a weaker time dependence that the ballistic motion, is present over 1-2 decades of intermediate times. Such a crossover corresponds to the wellknown caging regime [11,12,13,14,15,16,17,18] observed in supercooled liquids or dense colloidal systems. Due to the presence of the neighboring obstacles, the particle is trapped within an "effective cage" for some time until it escapes from it and begins to show a diffusive behavior.…”

Section: Mean-squared Displacementsmentioning

confidence: 99%

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Dynamics of a rod in a homogeneous/inhomogeneous frozen disordered medium: Correlation functions and non-Gaussian effects

Moreno¹

2004

AIP Conference Proceedings

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We present molecular dynamics simulations of the motion of a single rigid rod in a disordered static 2d-array of disk-like obstacles. Two different configurations have been used for the latter: A completely random one, and which thus has an inhomogeneous structure, and an homogeneous "glassy" one, obtained from freezing a liquid of soft disks in equilibrium. Small differences are observed between both structures for the translational dynamics of the rod center-of-mass. In contrast to this, the rotational dynamics in the glassy host medium is strongly slowed down in comparison with the random one. We calculate angular correlation functions for a wide range of rod length L and density of obstacles ρ as control parameters. A two-step decay is observed for large values of L and ρ, in analogy with supercooled liquids at temperature close to the glass transition. In agreement with the prediction of the Mode Coupling Theory, a time-length and time-density scaling is obtained. In order to get insight on the relation between the heterogeneity of the dynamics and the structure of the host medium, we determine the deviations from Gaussianity at different length scales. Strong deviations are obtained even at spatial scales much larger than the rod length. The magnitude of these deviations is independent of the nature of the host medium. This result suggests that the large scale translational dynamics of the rod is affected only weakly by the presence of inhomogeneities in the host medium.

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“…These polymorphs distinguished by the correlation between neighboring dihedral angles. The amorphous selenium has relatively low molecular weight polymer with low concentration of rings (Bichara & pellegatti, 1993, Caprion & Schober, 2000& 2002, Echeveria et. al., 2003, Malek et.…”

Section: Binary Chalcogenidesmentioning

confidence: 99%

Crystallization Kinetics of Chalcogenide Glasses

Singh¹

2012

Crystallization - Science and Technology

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Structure and relaxation in liquid and amorphous selenium

Cited by 73 publications

References 55 publications

Anomalous high-pressure behavior of amorphous selenium from synchrotron x-ray diffraction and microtomography

Anomalous high-pressure behavior of amorphous selenium from synchrotron x-ray diffraction and microtomography

Dynamics of a rod in a homogeneous/inhomogeneous frozen disordered medium: Correlation functions and non-Gaussian effects

Crystallization Kinetics of Chalcogenide Glasses

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