Structural relaxation as seen by quasielastic neutron scattering on viscous Zr–Ti–Cu–Ni–Be droplets
Structural relaxation as seen by quasielastic neutron scattering on viscous Zr–Ti–Cu–Ni–Be droplets
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粘性 Zr-Ti-Cu-Ni-Be 液滴上的准弹性中子散射所见的结构弛豫
DOI：
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发表时间：
2011
期刊：
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通讯作者：
A. Meyer
中科院分区：
文献类型：
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作者：
Fan Yang;Tobias Kordel;D. Holland;T. Unruh;A. Meyer
在大块非晶形成的Zr46.8Ti8.2Cu7.5Ni10Be27.5(Vit4)中，镍、钛和铜在液相线的平均自扩散系数约为10−10 m2 S−1。与这些值相比，由各种已报道的粘度数据通过斯托克斯-爱因斯坦关系重新标度得到的扩散系数表现出不同的温度依赖性，绝对值小5-10倍。这就提出了一个问题：当熔体的温度远高于液相线温度时，熔体中是否存在一个缓慢的锆子系统。在这里，我们通过研究利用准弹性中子散射的微观动力学来解决这个问题。我们在一种新型的静电悬浮装置中使用了无容器样品处理。这排除了样品和坩埚材料之间的反应，并提供了大约0.22.6ä−1的广泛动量传递范围。我们研究了由Ni、Ti和Cu扩散运动以及集体Zr运动控制的动力学。在1255K，两个关联函数在约20ps的时间尺度上都衰减到零。这表明在平衡熔体中既不存在各组分的原子动力学之间的解耦，也不存在缓慢的锆子系统。
In bulk glass forming Zr46.8Ti8.2Cu7.5Ni10Be27.5 (Vit4) the mean Ni, Ti, and Cu self-diffusion coefficient at the liquidus is about 10 − 10 m2 s − 1. Compared with these values, diffusion coefficients derived from various reported viscosity data by rescaling them via the Stokes–Einstein relation exhibit different temperature dependence and absolute values are a factor of 5–10 smaller. This raises the question of whether a slow Zr subsystem exists in the melt at temperatures well above the liquidus temperature. Here, we address this question by studying microscopic dynamics employing quasielastic neutron scattering. We utilized containerless sample processing in a novel electrostatic levitation apparatus. This excludes reactions between samples and crucible materials and gives access to a wide momentum transfer range of about 0.2–2.6 Å − 1. We studied the dynamics governed by the Ni, Ti, and Cu diffusive motion as well as by collective Zr motion. At 1255 K, both correlation functions decay to zero on a timescale of about 20 ps. This shows that there is neither a decoupling between the atomic dynamics of the various components nor a slow Zr subsystem in the equilibrium melt.