Thermoelectric Performance Improvement in the ZrNiSn-Based Composite via Modulating Si Addition

To ensure optimal performance, ZrNiSn is required to possess a low thermal conductivity and exhibit minimal bipolar effects under high-temperature conditions. This study demonstrates the integration of silicon (Si) at different doping levels into ZrNiSn. The composites consist of secondary phases of in situ ZrNiSi and Si. At a temperature of 873 K, the Seebeck coefficient experiences a 16% increase, despite the charge carrier concentration increasing three times as a result of the electron injection from ZrNiSi. The phenomenon can be elucidated by the introduction of Si, which causes energy filtering and inhibits the flow of minority charge carriers. When the doping levels in n- or p-type Si reach high levels (10¹⁹ to 10²⁰ cm^-3), the mixed interfaces ZrNiSn/ZrNiSi and ZrNiSn/Si reduce the thermal conductivity by 15%, resulting in a 50% increase in zT. These findings indicate that electron transfer in ZrNiSn can be regulated by precise doping in Si. They also demonstrate that incorporating an optimal p-type semiconductor can enhance the thermoelectric performance of n-type ZrNiSn. Additionally, a novel approach is proposed to separate electrical conductivity and the Seebeck coefficient by designing unique secondary phase interfaces.