Transition Elements and Nucleation in Glasses Using X-ray Absorption Spectroscopy

Selected results on the environment around Zr, Ti, and Ni in glasses and glass-ceramics using X-ray absorption spectroscopy (XAS) are presented to illustrate how this technique can provide information on the nucleation/crystallization processes. These elements actively participate to nucleation and, additionally, some of them bring new optical properties to the material. We show that extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) information, at K-edge or L-2,L-3-edges, can give short and medium range structural and bonding information. Nucleation activity of transition elements cannot be concluded from their local environment within the investigated parent glasses (at least for Zr and Ti, the main nucleating agents). On the contrary, medium range organization is important to understand nucleation processes with the evidence of heterogeneities or structural fluctuations that can be directly related to the first crystallizing phases. New developments in the spatial resolution or in situ high temperature measurements show the utility of the XAS technique with environmental changes around transition elements that can be detected prior to macroscopic crystallization. This can be useful to determine whether a specific ion (e. g., Ni2+) enters the crystalline phase and in which site, allowing a better control of the temperature or crystallization kinetics to optimize the material properties.

本文介绍了利用X射线吸收光谱（XAS）对玻璃和微晶玻璃中Zr、Ti和Ni周围环境的部分研究结果，以说明该技术如何为成核/结晶过程提供信息。这些元素积极参与成核，此外，其中一些元素还为材料带来了新的光学性能。我们表明，在K边或L - 2、L - 3边的扩展X射线吸收精细结构（EXAFS）和X射线吸收近边结构（XANES）信息能够提供短程和中程的结构及键合信息。从所研究的母体玻璃中过渡元素的局部环境（至少对于主要的成核剂Zr和Ti而言）无法推断出其成核活性。相反，中程结构对于理解成核过程非常重要，因为有证据表明不均匀性或结构波动与最初的结晶相直接相关。空间分辨率或原位高温测量方面的新进展表明，XAS技术在过渡元素周围环境变化方面具有实用性，这些变化在宏观结晶之前就能被检测到。这对于确定特定离子（例如Ni²⁺）是否进入结晶相以及进入哪个位置很有用，从而能够更好地控制温度或结晶动力学以优化材料性能。