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Abstract:
The effect of Ti substitution by Sc on the thermoelectric properties of
the Heusler compounds NiTi0.3-xScxZr0.35Hf0.35Sn (where 0 < x <= 0.05)
was studied. The thermoelectric properties were investigated by
measuring the electrical conductivity, Seebeck coefficient, and thermal
conductivity. A reduction of the thermal conductivity by a factor of 2
was obtained by substitution of Ti by Sc. The pure compound
NiTi0.3Zr0.35Hf0.35Sn showed n-type conductivity with a Seebeck
coefficient of -288 mu V/K at 350 K, while under Sc substitution the
system switched to p-type behavior. A maximum Seebeck coefficient of
+230 mu V/K (350 K) was obtained by 4% Sc substitution, which is the
highest value for p-type thermoelectric compounds based on Heusler
alloys. The electronic structure was studied by photoelectron
spectroscopy excited by hard x-ray synchrotron radiation. Massive in gap
states are observed for the parent compound. This proves that the
electronic states close to the Fermi energy play a key role on the
behavior of the transport properties. Especially, they are responsible
for the high, negative Seebeck coefficient of the parent compound. (C)
2010 American Institute of Physics. [doi:10.1063/1.3531662]
