Effect of Sb Doping on the Thermoelectric Properties of MNiSn (M=Ti, Zr, Hf) Half-Heusler Alloys Fabricated by a Rapid Solidification Process

초록

Among half-Heusler alloys, MNiSn (M = Ti, Zr, Hf) compounds have been extensively investigateddue to their unique crystal structure and promising thermoelectric properties. However, forming the MNiSnhalf-Heusler single phase directly during the solidification process is challenging, necessitating a prolongedannealing step for homogenization. Rapid Solidification Processing (RSP) was employed to synthesizematerials with controlled microstructures and high thermoelectric performance within a short processingtime. Optimized RSP processes were then used to produce ribbon-shaped samples, aiming to enhancethermoelectric performance through grain size reduction and the synthesis of half-Heusler alloys withminimal amounts of detrimental phases. In the alloy design step, Ti, Zr, and Hf were typically mixed at theM sites to reduce lattice thermal conductivity. To address cost and production efficiency concerns associatedwith incorporating Hf, alloy compositions with reduced Hf content were designed. A comparative analysis ofthe thermoelectric properties of Ti0.5Zr0.17Hf0.33NiSn(1-x)Sbx (x = 0.02~0.08) was conducted by varying dopinglevels of Sb as the dopant element. The addition of Sb led to a gradual increase in electron concentration,resulting in a significant rise in electrical conductivity. However, this increase in electronic thermalconductivity had a detrimental effect on the overall dimensionless Fig. of merit ZT value. The maximum ZTvalue of 0.92 was achieved in Ti0.5Zr0.17Hf0.33NiSn0.98Sb0.02 at 773K, demonstrating the potential of Hf-reducedhalf-Heusler alloys synthesized by RSP for thermoelectric applications.

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