The slow β, or Johari–Goldstein (JG) relaxation process, has been widely observed in glasses and is known to induce the stress relaxation associated with mechanical properties. So far, jumping motions of only a fraction of the particles were believed to contribute to the JG process in glass. However, there is no direct experimental evidence of the atomic-scale images due to the difficulties in microscopic observation. In this study, atomic motions in the quasi-spherical model ionic-glass-former Ca_0.4K_0.6(NO₃)_1.4 were microscopically observed with one-angstrom resolution, the highest resolution to date, using X-ray time-domain interferometry. The microscopic experiment directly indicated that most particles underwent angstrom-scale motions in the time scale of the JG relaxation. This result was further supported by molecular dynamics (MD) simulations. A combined study of experiments and MD simulations revealed that most particles contributed to the JG process through unexpected collective nonjumping motions with angstrom-scale displacement, activated by jumping motions of a fraction of particles. The discovery of nonjumping motions by our atomic-scale dynamic observations has considerably advanced our understanding of the puzzling mechanism of the JG process.

中文翻译：

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在模型离子玻璃中发现导致应力松弛的 Johari-Goldstein 过程的集体非跳跃运动


慢速β或 Johari-Goldstein （JG） 弛豫过程已在眼镜中广泛观察到，并且已知会诱导与机械性能相关的应力弛豫。到目前为止，只有一小部分颗粒的跳跃运动被认为有助于玻璃中的 JG 过程。然而，由于显微镜观察的困难，没有原子尺度图像的直接实验证据。在这项研究中，使用 X 射线时域干涉测量法，以 1 埃分辨率（迄今为止最高的分辨率）微观观察准球形模型离子玻璃形成剂 Ca_0.4K_0.6（NO₃）_1.4 中的原子运动。微观实验直接表明，大多数粒子在 JG 弛豫的时间尺度上经历了埃尺度的运动。分子动力学 （MD） 模拟进一步支持了这一结果。实验和 MD 模拟的联合研究表明，大多数粒子通过具有埃级位移的意外集体非跳跃运动对 JG 过程做出贡献，由一小部分粒子的跳跃运动激活。通过原子尺度动力学观测发现非跳跃运动，大大推进了我们对 JG 过程令人费解的机制的理解。