High thermoelectric figure of merit by resonant dopant in half-Heusler alloys

Abstract

Half-Heusler alloys have been one of the benchmark high temperature thermoelectric materials owing to their thermal stability and promising figure of merit ZT. Simonson et al. early showed that small amounts of vanadium doped in Hf 0.75 Zr 0.25 NiSn enhanced the Seebeck coefficient and correlated the change with the increased density of states near the Fermi level. We herein report a systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta) as prospective resonant dopants in enhancing the ZT of n-type half-Heusler alloys based on Hf 0.6 Zr 0.4 NiSn 0.995 Sb 0.005. The V doping was found to increase the Seebeck coefficient in the temperature range 300-1000 K, consistent with a resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as evident by the systematic decrease in electrical resistivity and Seebeck coefficient. The combination of enhanced Seebeck coefficient due to the presence of V resonant states and the reduced thermal conductivity has led to a state-of-the-art ZT of 1.3 near 850 K in n-type (Hf 0.6 Zr 0.4 ) 0.99 V 0.01 NiSn 0.995 Sb 0.005 alloys .

Electronic, optical and thermoelectric properties of Fe2ZrP compound determined via first-principles calculations

“…[5][6][7][8] In recent years, Heusler compounds have been theoretically investigated, and their TE properties have attracted signicant attention from researchers. [9][10][11][12][13][14][15][16][17] Generally, Heusler compounds have the stoichiometric composition XYZ or X 2 YZ and crystallize in the L2 1 structure, where X and Y are transition or rareearth metals and Z is the main group element. 18 These materials are half-metallic, where one spin channel shows metallicity, whereas the other spin channels are completely semiconducting.…”

“…Because of this feature, half-metallic Heusler alloys can be considered as the most important class of spintronic materials. [19][20][21][22][23] Half-metallic material alloys have been found in some kinds of materials such as full 16,[24][25][26][27][28][29] and half Heusler alloys, 15,30,31 binary compounds [32][33][34] and 2D materials. [35][36][37] Recently, in a theoretical study, the effect of Ge substitution on the thermoelectric properties of the Heusler-type alloy Fe 2 -MnSi x Ge 1Àx has been investigated by Reshak.…”

The half Heusler system Ti1+xFe1.33−xSb–TiCoSb with Sb/Sn substitution: phase relations, crystal structures and thermoelectric properties

“…So far the highest ZT = 1.5 has been reported by Sakurada and Shutoh 10 for Sb-doped n-type Ti 0.5 Zr 0.25 Hf 0.25 NiSn 0.998 Sb 0.002 at 690 K and by Rogl et al 11 at a slightly higher temperature of 825 K. Schwall and for (Zr 0.40 Hf 0.60 ) 0.00 V 0.01 NiSn 0.998 Sb 0.002 with vanadium resonant states. 13 For commercial thermoelectric applications, however, the high priced Hf-metal needs to be avoided. Therefore, it is interesting to note that for the Hf-free grades Ti 0.5 Zr 0.5 NiSn 0.98 Sb 0.02 14 and Ti 0.50 Zr 0.48 Nb 0.02 NiSn 0.98 Sb 0.02 , 11 a ZT = 1.2 was obtained with a thermoelectric efficiency η 300-800 K > 11%.…”

Recent Advances in Thermoelectric Performance of Half-Heusler Compounds

“…The correlation between the enhanced Seebeck coefficient and increased DoS near the Fermi level was confirmed by specific heat measurement. Stimulated by the success in improving zT by reducing the lattice strain, we also explored whether further improvement in zT could be obtained by doping one of the zT > 1 HH compounds, namely, n-type Hf0.6Zr0.4NiSn0.995Sb0.005, with VA group elements V, Nb, and Ta [13].…”