Thermoelectric Properties of NbCoSn-based Half-Heusler Alloys

Thermoelectric properties of doped half-Heuslers, NbCoSn
_1-x
Sb
_x
and Nb
_0.99
Ti
_0.01
CoSn
_1-x
Sb
_x
, have been studied in the temperature range from 320 K to 850 K. These half-Heuslers were synthesized by the arc-melting of pure metals followed by annealing for one week at 1123 K in vacuum. The samples with x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10 are prepared by the spark plasma sintering, SPS, method using fine powders of the crushed arc-melted buttons. Sintered samples are of nearly single phase. All the samples exhibit metal-like temperature dependent rho of the order of 10
^-6
-10
^-5
Omega-m in the measured temperature range. In both NbCoSn
_1-x
Sb
_x
and Nb
_0.99
Ti
_0.01
CoSn
_1-x
Sb
_x
, the rho values at 320 K rapidly decrease by the partial substitution in the range between x = 0 and 0.02, and finally reach 5 muOmegamiddotm at x = 0.10. Seebeck coefficient, S, is appreciably enhanced by partly substituting the Nb site with 1 at.% of Ti. The highest power factor is 22 times 10
^-4
Wmiddotm
^-1
middotK
^-2
for Nb
_0.99
Ti
_0.01
CoSn
_0.9
Sb
_0.1
at 700 K. The thermal conductivity, kappa, weakly depends on temperature and does not show any peculiar trend due to Sb partial substitution. Dimensionless figure of merit, ZT = S
²
T/rhokappa, for Nb
_0.99
Ti
_0.01
CoSn
_0.9
Sb
_0.1
reaches 0.3 at 850 K, which is four times higher than that of the pure NbCoSn