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Pressure-Induced Phase Transformation of Quasicrystals

准晶的压力诱导相变

基本信息

批准号：
03650530
负责人：
KAWAMURA Haruki
金额：
$ 1.15万
依托单位：
Himeji Institute of Technology Grant-in-Aid for Scientific Research (C)
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-03650530/
关键词：
Quasicrystal High pressure X-ray diffraction Phase transformation 相転移

项目摘要

Since the discovery of quasicrystals with an icosahedral symmetry, there has been a great deal of effort to investigate their stability or structure. Quasicrystals were obtained as metastable phase (i-Al-Mn) at first, but now are synthesized also as thermodynamically stable phase (i-Al-Li-Cu, i-Al-Ru-Cu). To investigate the stability of quasicrystals, we have performed x-ray diffraction experiment under high pressure.For Al-Mn and Al-Ru-Cu, the i-phase was isotropically compressed and stable up to 23 and 30 GPa, respectively. On the other hand, in Al-Li-Cu i-phase, a successive phase transformation was observed to occur in two stage under high pressure. The first is from the i-phase to an amorphous state. The transition starts at the pressure of around 10 GPa, and the i-phase and the amorphous phase coexist over a wide pressure range. After disappearance of the i-phase, the second stage of transition from the amorphous to a long-range ordered state was caused by application of pressure of around 28 GPa.To reveal details of the transition from the i-phase to the amorphous phase, we measured the dependence of x-ray diffraction peak widths on pressure. Peak widths of all lines become broader with an increase in pressure but the increment of the peak widths exhibited no clear systematic dependence on momentum transfer (G_*) nor phason momentum (G_*). Such a G-independent broadening of x-ray peaks suggests that a fragmentation of the structure takes place on increasing the pressure. The fragmentation of the structure may possibly be realized by producing variants of small grains of approximate crystals by introducing phasons. High temperature experiments were also performed at the pressure where the i-phase and the amorphous phase coexist. At around 100 ﾟC, the i-phase was more stable than the amorphous phase, but at around 250 ﾟC, the i-phase turned into crystal phase.

自从发现具有二十面体对称性的准晶以来，人们一直在努力研究它们的稳定性或结构。准晶最初是以亚稳相（i-Al-Mn）的形式合成的，但现在也合成了以热力学稳定相（i-Al-Li-Cu，i-Al-Ru-Cu）的形式。为了研究准晶的稳定性，我们在高压下进行了X射线衍射实验，结果表明：Al-Mn和Al-Ru-Cu的i相在23 GPa和30 GPa的压力下是各向同性压缩的，并且是稳定的。Al-Li-Cu i相在高压下发生两阶段连续相变。第一个是从i相到非晶态。转变开始于约10 GPa的压力，i相和非晶相共存在一个宽的压力范围内。消失后的i相，从非晶到长程有序状态的过渡的第二阶段所造成的压力约28 GPa的应用程序。为了揭示从i相到非晶相的过渡的细节，我们测量的X射线衍射峰宽度对压力的依赖性。所有谱线的峰宽都随压力的增加而变宽，但峰宽的增加与动量传递（G *）和相子动量（G *）没有明显的系统关系。这种与G无关的X射线峰的加宽表明，在增加压力时发生结构的碎裂。通过引入相子产生近似晶体的小晶粒的变体，可以实现结构的破碎。在i相和非晶相共存的压力下进行了高温实验。在100 ℃左右，i相比非晶相更稳定，但在250 ℃左右，i相变成晶相。