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Structure and Dynamics of Excited States in Glasses Studied by Pulsed Neutron Scattering

脉冲中子散射研究玻璃激发态的结构和动力学

基本信息

批准号：
10440094
负责人：
ARAI Masatoshi
金额：
$ 8.19万
依托单位：
High Energy Accelerator Research Organization
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10440094/
关键词：
pulsed neutron source medium range order inelastic neutron scattering phonon dispersion relation dynamical structure factor boson peak non-crystalline materials ガラスダイナミクス中性子

项目摘要

The dynamical structure factors S(Q,E) of SiOィイD22ィエD2 glass and NiィイD267ィエD2ZrィイD233ィエD2 glass were measured by inelastic neutron scattering. The advance of pulsed neutron scattering technique enabled us to obtain the S(Q,E) in a wide momentum-energy space with high resolution and high neutron flux.The dispersive excitations in these glasses are clearly observed for the first time, whose periodicity is defined by the respective static structure factors S(Q). This feature suggests the existence of quasi-Brillouine zone which originate from short range structure. However, the first sharp diffraction peak in S(Q), which correlate with the medium range order of glass structure, has no relation with dispersive behavior. The dispersive excitations in SiOィイD22ィエD2 glass is acoustic-like behavior, while that of NiィイD267ィエD2ZrィイD233ィエD2 glass optic-like one. This difference may be attributed to the rigidity of short range structure. It is considered that NiィイD267ィエD2ZrィイD233ィエD2 glass has no rigid structural units which surely appear in SiOィイD22ィエD2 glass. The Boson peak, which is a universal feature of glassy materials, is also proved to be strongly localized mode.It must be noted that the dispersive behavior exists above the energy range of Boson peak. Our result is contrary to the Ioffe-Regel criteria which argue that no collective excitations should exist above an energy determined from correlation length of local density fluctuation. We can say that the observations of dynamic structure factor S(Q,E) over a wide range of momentum-energy space bring us fruitful information on structure and dynamics of glassy materials.

用中子非弹性散射法测量了SiO_2 O_2玻璃和Ni_2 O_2玻璃的动力学结构因子S（Q，E）。脉冲中子散射技术的发展使我们能够在宽动量-能量空间内获得高分辨率和高中子通量的S（Q，E），并首次清晰地观察到了这些玻璃中的色散激发，其周期性由各自的静态结构因子S（Q）定义。这一特征表明存在着源于短程构造的类布里渊区。而S（Q）中的第一个尖锐衍射峰与玻璃结构的中程有序度有关，与色散行为无关。SiO_（22）Al_（23）Al_（2这种差异可能归因于短程结构的刚性。认为Ni_（267）Zr_（233）Zr_（233）D_2玻璃不具有SiO_（22）Zr_（233）D_2玻璃中必然存在的刚性结构单元。玻色峰是玻璃材料的普遍特征，也证明了玻色峰是强局域模，必须指出的是，在玻色峰的能量范围以上存在色散行为。我们的结果与Ioffe-Regel准则相反，该准则认为在由局部密度波动相关长度确定的能量以上不应存在集体激发。我们可以说，动态结构因子S（Q，E）在很宽的动量-能量空间范围内的观测为我们提供了丰富的关于玻璃材料结构和动力学的信息。