微波快速合成—烧结制备ZrNiSn半赫斯勒热电合金

Rapid Microwave Synthesis and Sintering of ZrNiSn Half-Heusler Thermoelectric Alloy

开展了ZrNiSn热电块体材料的微波快速合成-烧结研究,并对样品的物相组成、电性能、热性能、微观结构和综合热电性能进行了测试和表征分析。相组成分析表明,采用微波固相合成在4~5 min内即获得了单一相纯度很高的ZrNiSn合金,但存在少量杂质Sn;合成样品经30 min微波烧结后,部分Sn因二次反应而消除。电性能分析表明,电阻率较高为13.7~16.9μ?·m,从而对功率因子产生较大影响,功率因子最高为1683μW·m^(-1)·K^(-2)。热性能分析表明,ZrNiSn样品的热导率随着温度升高而降低,热导率最大为4.288 W·m^(-1)·K^(-1),晶格热导率仅为2.86~3.96 W·m^(-1)·K^(-1),热性能良好。微观结构分析表明,微波烧结抑制了ZrNiSn晶粒长大,ZrNiSn基体晶内和晶界分布有大量纳米晶粒,绝大部分属于晶内析出,且分布较均匀,少部分分布在晶界。综合热电性能ZT值随测试温度的增加显著上升,在573~673 K获得最大值0.25。

The rapid microwave synthesis and sintering of Zr Ni Sn bulk was studied. The phase composition and microstructure of samples were characterized by X-ray diffractometer（XRD） and transmission electron microscope（TEM）, respectively. The thermoelectric properties i.e. Seebeck coefficient（S）, electrical resistivity（ρ）, and thermal conductivity（κ） were measured through Seebeck coefficient/resistance analysis system（S/RAs） and laser flash thermal analyzer（LFT）. The results show that a relatively high purity single phase of Zr Ni Sn alloy is synthesized within 4～5 min in microwave field, and a small amount of impurity Sn is almost eliminated by 30 min microwave sintering via secondary reaction. The variation trends of S, ρ and power factor with temperature were analyzed. The electrical resistivity is relatively high, 13.7～16.9 μ？·m. The highest power factor is 1683 μW·m～（-1）·K^（-2）, lower than the previously reported, which should be attributed to the high electrical resistivity. The thermal conductivity is decreased with temperature, and its maximum value is 4.288 W·m^（-1）·K^（-1）. The lattice thermal conductivity is merely 2.86～3.96 W·m^（-1）·K^（-1）. The microstructure analysis shows that the growth of Zr Ni Sn grain is inhibited during microwave sintering. A large number of nanometer grains are precipitated in the interior of Zr Ni Sn grain and on the boundary. The calculated thermoelectric figure of merit（ZT） is rapidly increased with temperature, and a maximum ZT of 0.25 is achieved at 573～673 K.