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Structural origins of the boson peak in metals: From high-entropy alloys to metallic glasses

Brink, Tobias and Koch, Leonie and Albe, Karsten (2016):
Structural origins of the boson peak in metals: From high-entropy alloys to metallic glasses.
In: Physical Review B, pp. 224203(1, 94, (22), ISSN 2469-9950, [Online-Edition: http://dx.doi.org/10.1103/PhysRevB.94.224203],
[Article]

Abstract

The boson peak appears in all amorphous solids and is an excess of vibrational states at low frequencies compared to the phonon spectrum of the corresponding crystal. Until recently, the consensus was that it originated from “defects” in the glass. The nature of these defects is still under discussion, but the picture of regions with locally disturbed short-range order and/or decreased elastic constants has gained some traction. Recently, a different theory was proposed: The boson peak was attributed to the first van Hove singularity of crystal lattices which is only smeared out by the disorder. This new viewpoint assumes that the van Hove singularity is simply shifted by the decreased density of the amorphous state and is therefore not a glass-specific anomaly. In order to resolve this issue, we use computer models of a four-component alloy, alternatively with chemical disorder (high-entropy alloy), structural disorder, and reduced density. Comparison to a reference glass of the same composition reveals that the boson peak consists of additional vibrational modes which can be induced solely by structural disorder. While chemical disorder introduces fluctuations of the elastic constants, we find that those do not lead to sufficient local softening to induce these modes. A boson peak due to a reduction of density could be excluded for the present metallic system.

Item Type: Article
Erschienen: 2016
Creators: Brink, Tobias and Koch, Leonie and Albe, Karsten
Title: Structural origins of the boson peak in metals: From high-entropy alloys to metallic glasses
Language: English
Abstract:

The boson peak appears in all amorphous solids and is an excess of vibrational states at low frequencies compared to the phonon spectrum of the corresponding crystal. Until recently, the consensus was that it originated from “defects” in the glass. The nature of these defects is still under discussion, but the picture of regions with locally disturbed short-range order and/or decreased elastic constants has gained some traction. Recently, a different theory was proposed: The boson peak was attributed to the first van Hove singularity of crystal lattices which is only smeared out by the disorder. This new viewpoint assumes that the van Hove singularity is simply shifted by the decreased density of the amorphous state and is therefore not a glass-specific anomaly. In order to resolve this issue, we use computer models of a four-component alloy, alternatively with chemical disorder (high-entropy alloy), structural disorder, and reduced density. Comparison to a reference glass of the same composition reveals that the boson peak consists of additional vibrational modes which can be induced solely by structural disorder. While chemical disorder introduces fluctuations of the elastic constants, we find that those do not lead to sufficient local softening to induce these modes. A boson peak due to a reduction of density could be excluded for the present metallic system.

Journal or Publication Title: Physical Review B
Volume: 94
Number: 22
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ) > Hochleistungsrechner
11 Department of Materials and Earth Sciences > Material Science
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ)
11 Department of Materials and Earth Sciences
Zentrale Einrichtungen
Date Deposited: 16 Dec 2016 12:10
Official URL: http://dx.doi.org/10.1103/PhysRevB.94.224203
Identification Number: doi:10.1103/PhysRevB.94.224203
Funders: Financial support by the Deutsche Forschungsgemeinschaft (DFG) through Grant No. AL 578/6-2, as well as a travel grant to Finland through the PPP program of the Deutscher Akademischer Austauschdienst (DAAD) are gratefully acknowledged.
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