通过悬浮熔炼的方法制备了half-Heusler热电材料Zr(Hf)NiSn(Sb)合金, 并进一步通过快速凝固来细化晶粒, 通过放电等离子烧结制备块材并测试其热电性能. X射线衍射分析表明获得了单相Half-Heusler化合物. 扫描电子显微观察发现, 快速凝固后的样品晶粒尺寸在500nm左右, 放电等离子烧结后晶粒尺寸并未明显长大. 同时观察到在晶粒的表面还分布了很多几十纳米尺寸的小晶粒. 快速凝固的样品与熔炼样品相比具有较高的电导率及载流子浓度, 据此推断在快速凝固过程中产生的纳米晶粒应为金属相. 快速凝固后的样品晶界散射增多, 因而具有较低的晶格热导率.
Thermoelectric materials Zr(Hf)NiSn(Sb) alloys were prepared by levitation melting followed by melt- spinning to refine the microstructure, and then consolidated by spark plasma sintering for the property measurements. XRD analysis showed that the half-Heusler phases were obtained. The microstructures of the melt spun thin ribbons were studied by the scanning electron microscope and transmission electron microscope. The thin ribbons were in the size of a few hundreds nanometers which didn’t grow too much during the sintering process. Nanocrystals were found in the crystal grains. The carrier concentration increased for the melt-spinning samples compared with the levitation melting samples, indicating that the nanocrystals were metallic. The increasing boundary scattering after melt-spinning made the lattice thermal conductivity decrease.
参考文献
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