Thermoelectric properties and electronic structure of substituted Heusler compounds: NiTi0.3-xScxZr0.35Hf0.35Sn.

The effect of Ti substitution by Sc on the thermoelectric properties of the Heusler compounds NiTi_0.3-xSc_xZr_0.35Hf_0.35Sn (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 NiTi_0.3Zr_0.35Hf_0.35Sn showed n-type conductivity with a Seebeck coefficient of -288 μV/K at 350 K, while under Sc substitution the system switched to p-type behavior. A maximum Seebeck coefficient of +230 μV/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. [ABSTRACT FROM AUTHOR]