Structural origins of the boson peak in metals: From high-entropy alloys to metallic glasses
Structural origins of the boson peak in metals: From high-entropy alloys to metallic glasses
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DOI：
10.1103/physrevb.94.224203
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发表时间：
2016-12-14
影响因子：
3.7
通讯作者：
Albe, Karsten
中科院分区：
文献类型：
--
作者：
Brink, Tobias;Koch, Leonie;Albe, Karsten
玻色子峰出现在所有非晶固体中，并且与相应晶体的声子谱相比，在低频下是过量的振动态。直到最近，人们的共识是，它起源于玻璃中的“缺陷”。这些缺陷的性质仍在讨论中，但局部干扰短程有序和/或弹性常数降低的区域的图片已经获得了一些牵引力。最近，一种不同的理论被提出：玻色子峰被归因于晶格的第一个货车霍韦奇异性，它只被无序所模糊。这个新的观点假设，货车霍韦奇异性是简单地移动的密度降低的非晶态，因此不是一个玻璃特有的异常。为了解决这个问题，我们使用四组分合金的计算机模型，交替使用化学无序（高熵合金），结构无序和约化密度。与相同组成的参考玻璃的比较表明，玻色子峰由可以仅由结构无序引起的额外的振动模式组成。虽然化学无序引入的弹性常数的波动，我们发现，这些不会导致足够的局部软化，以诱导这些模式。对于本金属系统，可以排除由于密度降低而导致的玻色子峰。
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.