Zone melting of Bi0,5Sb1,5Te3 crystals under microgravity
Zone melting of Bi0,5Sb1,5Te3 crystals under microgravity
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DOI：
10.1002/(sici)1521-4079(1998)33:2
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发表时间：
1998
影响因子：
1.5
通讯作者：
F. König
中科院分区：
文献类型：
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作者：
F. König
在1994年俄罗斯“和平号”空间站的空间飞行中，用区熔法生长了两个Bi_（0.5）Sb_（1.5）Te_3热电材料样品。通过将飞行样品与参考地面样品进行比较，可以得出关于熔体中不同质量传输情况对微观和宏观偏析的影响的相关结论。通过SEEBeck系数的局部分辨扫描和WDX测量，对样品进行金相分析。与地面样品相反，飞行样品显示在大体积中没有对流引起的条纹。因此，在微重力条件下，避免了熔体中的不稳定流动。飞行样品中Te组分的轴向分布显示出意想不到的Pfann样行为，这表明对流控制的生长。与此相反，金属组分的轴向分布是扩散控制的。在飞行样品中发现的碲的轴向宏观偏析可以解释为具有低分布系数的组分对最弱对流的高灵敏度。与地面样品相比，飞行样品中Te分量的径向分布更均匀。这些差异的解释仅部分成功的界面的曲率和Te浓度边界层的变化跨越界面。
Two samples of the thermoelectrical material Bi0.5Sb1.5Te3 were grown by zone melting technique during a space flight of the russian space station “MIR” in 1994. By comparing the flight samples with the reference ground samples relevant conclusions regarding the influence of different mass transport situations in the melt on micro- and macrosegregation are possible. The samples were analyzed metallographically, by local resolved scanning of the SEEBECK-coefficient and by WDX measurements. Contrary to the ground samples the flight samples showed no convection-induced striations in the bulk. Consequently under microgravity unsteady flow in the melt has been avoided. The axial distribution of the Te component in the flight samples showed an unexpected Pfann-like behaviour, which points to a convection-controlled growth. Contrary to this the axial distribution of the metal components was diffusion-controlled. The axial macrosegregation of tellurium found in the flight samples can be explained by the high sensitivity of components with a low distribution coefficient to weakest convective flows. The radial distribution of the Te component in the flight samples is more homogeneous compared to the ground samples. The explanation of these differences succeeds only partly by the curvature of the interface and by the variation of the Te concentration boundary layer across the interface.