Abstract
We report on the electrical resistivity and the Seebeck coefficient for the p-type half-Heusler compounds ZrNi1-xMxSn with M=Co, Rh and Ir, and x=0-0.30, in addition to the doping effect on the thermal conductivity at 300 K. While a slight substitution of Ir causes a significant decrease in the electrical resistivity at 300 K, the Co doping results in a large enhancement in the Seebeck coefficient, reaching 170 μV/K at 300 K for x=0.05. The net effect of doping is most likely to cause a modification in the band structure around the band gap. Although the thermal conductivity remains in the range of 6-7 W/mK for the Co substitution, it decreases more rapidly for the Ir substitution, reaching 2.6 W/mK at x=0.2. Further doping of heavier atoms like Hf for the Co substitution reduces more effectively the lattice thermal conductivity while retaining the low electrical resistivity as well as the large Seebeck coefficient, so that the thermal conductivity for Zr0.5Hf0.5Ni0.85Co0.15Sn is as low as 3.8 W/mK, in spite of the possession of a large power factor of the order of 10-3 W/mK2 at 800 K.
