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，将垂直于re电极的圆柱形透镜展开的蓝色氩离子激光（488nm）和红色二极管激光（690nm）同时照射到细颗粒上，通过彩色滤光片获得蓝光的顶视图和红光的侧面视图。用这种方法在同一位置同时观察顶视图和侧视图，可以进行准确的分析。库仑晶体结构的转变过程也可以每1/30秒进行一次分析。利用这些分析方法，我们观察到，在三维库仑晶体中，体心立方（bcc）状结构（011）或（001）面平行于电极，面心立方（fcc）状结构（111）面平行，六边形紧密堆积状结构（0001）平行。类bcc结构的三个晶格常数之比为1:1.56:1.53，表明该晶体应称为体心四边形（bct）晶格。对于类fcc结构，密排面的晶格常数与相邻平面之间的距离之比为1:0 .83，与fcc晶格之比非常接近。观察和分析了fcc和bct结构的共存以及两种结构之间的转变。结果表明，fcc（111）和bct（001）之间的晶面向fcc[110]和bct[111]方向滑移导致了结构变化。这种转变与碳钢的马氏体相变相对应。

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.