Phase Engineering Enabled Excellent Power Factor and Reduced Thermal Conductivity in ZrCoSb ‐Based Half‐Heusler Compounds

The output power density of thermoelectric (TE) devices scales with power factor (PF); thus, maximizing PF is crucial for TE materials with comparable dimensionless figure of merit ( zT ). Half‐Heusler (HH) alloys are promising for medium‐ and high‐temperature applications due to their thermal stability, but most studies focus on decoupling electrical transport parameters and reducing thermal conductivity, rather than enhancing PF by boosting electrical conductivity. Here, we report a phase engineering strategy for ZrCoSb‐based HH alloys that simultaneously improves electrical conductivity and reduces thermal conductivity. Introduced Si reacts with Zr and Co to form microscale semi‐metallic Zr ₆ Co ₁₆ Si ₇ precipitates, which inject holes into the matrix without degrading carrier mobility. Consequently, ZrCoSb _0.74 Sn _0.2 Si _0.06 achieves a high PF of 3.36 mW m ⁻¹  K ⁻² at 973 K, among the highest for p‐type ZrCoSb‐based TE materials. The abundant precipitates also suppress phonon transport, lowering lattice thermal conductivity. The combined enhancement of electrical conductivity and reduction of thermal conductivity leads to a peak zT of 0.65, a 38.3% improvement over the pristine sample. This work provides a new approach for PF optimization in HH alloys and offers insights for enhancing TE performance in other materials.