YbCd2-xMgxSb2 열전 합금의 열전 성능 증대 메커니즘 분석

초록

YbCd2Sb2 is a promising Zintl compound for waste heat recovery applications due to its low thermalconductivity, originating from its complex crystal structure. Many strategies such as alloying or doping havebeen suggested to further reduce the thermal conductivity of YbCd2Sb2 to improve its thermoelectricperformance. However, the effects of alloying or doping on the electronic transport properties of YbCd2Sb2have not been evaluated in detail. Here, previously reported thermoelectric properties of YbCd2-xMgxSb2 (x =0, 0.2, 0.4) with drastic thermal conductivity suppression were evaluated using the Single Parabolic Band(SPB) model and Callaway von Bayer (CvB) model. The SPB and CvB models evaluate any changes inelectronic band parameters and phonon scattering strength, respectively, due to Mg alloying. Based on theSPB model, Mg alloying deteriorated the weighted mobility, mostly due to non-degenerate mobility reduction. However, the magnitude of point-defect phonon scattering significantly increased with Mg alloying, asevaluated by the CvB model. As a result, the maximum zT is achieved when x = 0.4 at 700 K despite thedecreased electronic transport properties from Mg alloying. Our work suggests that carefully designed alloyingcan improve the thermoelectric performance of the Zintl compound even when it changes its electronic andthermal transport properties in opposite directions.

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