Analyses of Phase Transition by Coulomb Crystals in Fine-Particle Plamas

为了分析三维库仑晶体的三维结构，将蓝色氩离子激光（488 nm）和红色半导体激光（690 nm）同时照射到微细颗粒上，通过与稀土电极垂直的圆柱形透镜将其扩展，并通过彩色滤光片获得蓝色光的顶视图和红色光的侧视图。通过使用这种方法在同一时间和同一位置观察顶视图和侧视图，可以进行精确的分析。利用这些分析方法，我们在三维库仑晶体中观察到平行于电极的体心立方（bcc）类结构（011）或（001）面，平行于电极的面心立方（fcc）类结构（111）面，和平行的六边形紧密堆积状结构（0001）。体心立方结构的三个晶格常数之比为1：1.56：1.53，这表明该晶体应该被称为体心四方晶格（bct）。对于类面心立方结构，在密排平面中的晶格常数与相邻平面之间的距离的比率为1：0.83，这非常接近于面心立方晶格的比率。观察并分析了fcc和bct结构的共存以及两种结构之间的转变。根据该结果，确认了通过fcc（111）和bct（001）之间的晶面向fcc [110]和bct [111]方向的滑移而发生的结构变化。该转变对应于碳钢的马氏体转变。

In order to analyze the three-dimensional structure of three-dimensional Coulomb crystals, blue argon-ion-laser light (488nm) and red diode-laser light (690nm), which was expanded by a cylindrical lens perpendicular to an re electrode, were irradiated at the same time to fine-particles, and top views were obtained by the blue light and side views by the red light through a optical filter of the color. By the observation of top and side views at the same time and at the same position using this method, accurate analyses have become possible. The analysis of transition process of Coulomb crystal structures has become also possible every 1/30 seconds.Using these analytical methods, we observed, in three-dimensional Coulomb crystals, body-centered-cubic (bcc)-like structures (011) or (001) planes parallel to the electrode, face-centered-cubic (fcc)-like structures (111) planes parallel, and hexagonal-close-packed-like structures (0001) parallel. The ratio among three lattice constants for the bcc-like structure was 1 : 1.56 : 1.53, which shows that the crystal should be called the body-centered-tetragonal (bct) lattice. For the fcc-like structure, the ratio of the lattice constant in the close-packed plane to the distance between the neighboring planes was 1 : 0.83, which is very close to the ratio for fcc lattice. The coexistence of fcc and bct structures and the transition between the two structures were observed and analyzed. From the results, it was confirmed that the structural change occurred by the slip in crystal planes between fcc (111) and bct (001) to the direction of fcc [110] and bct [111]. The transition corresponds to the martensitic transformation of carbon steel.