Thermoelectric properties of Ni_0.15Co_3.85Sb₁₂ and Fe_0.2Ni_0.15Co_3.65Sb₁₂ skutterudites prepared by HPHT method

N-type polycrystalline skutterudite compounds Ni_0.15Co_3.85Sb₁₂ and Fe_0.2Ni_0.15Co_3.65Sb₁₂ with the bcc crystal structure were synthesized by high pressure and high temperature (HPHT) method. The synthesis time was sharply reduced to approximately half an hour. Typical microstructures connected with lattice deformations and dislocations were incorporated in the samples of Ni_0.15Co_3.85Sb₁₂ and Fe_0.2Ni_0.15Co_3.65Sb₁₂ after HPHT. Electrical and thermal transport properties were meticulously researched in the temperature range of 300 K to 700 K. The Fe_0.2Ni_0.15Co_3.65Sb₁₂ sample shows a lower thermal conductivity than that of Ni_0.15Co_3.85Sb₁₂. The dimensionless thermoelectric figure-of-merit (zT) reaches the maximal values of 0.52 and 0.35 at 600 K and 700 K respectively, for Ni_0.15Co_3.85Sb₁₂ and Fe_0.2Ni_0.15Co_3.65Sb₁₂ samples synthesized at 1 GPa.