Research on nano-microstructure control of the thermoelectric semiconductor by a solid phase process

碲化铋（Bi_2Te_3）基化合物在室温下具有菱面体结构，其大部分物理性质具有高度的各向异性。由于Bi_2Te_3化合物具有明显的垂直于c轴的（111）解理面，因此它们的力学性能和微加工性能较差，不能用于制备微型热电组件。将护套管改造为双层结构，即内部为铝管，外部为铜管。轧槽后，晶粒直径变小，结晶方向沿着轧制方向向a轴方向重新取向。这证明了纳米-微米结构控制是可能的。随着加工温度的变化，无掺杂的沟槽轧制Bi_2Te_3从137.0μV/K（473 K）的p型导电转变为-142.2 V/K（673 K）的n型导电。此外，后热处理改变了槽轧Bi_2Te_3的热电性能（300 K）。在性能的各向异性方面，Seebeck系数和热导率表现出较高的各向异性，且各向异性程度与铸锭或烧结体相同。Seebeck系数的值与烧结体相当，电阻率变为约2倍。导热系数降低约20%。通过沟槽轧制，晶粒的细化被加速。该制造工艺已申请专利。

Bismuth telluride (Bi_2Te_3) based compounds have a rhombohedral structure at room temperature and are distinguished by a high degree of anisotropy for most of the physical properties. Since the compounds have distinct (111) cleavage planes perpendicular to the c-aixs, they have low mechanical properties and poor ability in micro-processing for fabricating the miniature thermoelectric modules.The ingot and powder of Bi_2Te_3 was sealed in the sheath pipes and groove-rolled at 300K〜673K. The sheath pipe was modified to the dual structure, which was the Al pipe inside and Cu pipe outside. After the groove-rolled, the diameter of crystal grains became small, and the crystal direction along the rolling direction became the re-orientation to the a-axis. It proved that nano-micro structure control is possible. The groove-rolled Bi_2Te_3 with non-doping changed from the p-type conduction of 137.0μV/K (at 473K) to n-type conduction of -142.2μV/K (at 673K) by the processing-temperature. Moreover, post heat treatment changed thermoelectric properties of the groove-rolled Bi_2Te_3 (at 300K). As for the anisotropy of the properties, the Seebeck coefficient and thermal conductivity showed high anisotropy, and the degree of anisotropy was the same as the ingot or the sintered compact. The value of Seebeck coefficient was equivalent to the sintered compact, and resistivity became about 2 times. And thermal conductivity was lowered about 20%. The refinement of a crystal grain was accelerated by the groove-rolling. The patent of this manufacturing process applied.