In-gap Electronic States Responsible for the Excellent Thermoelectric Properties of Ni-based Half-Heusler Alloys

摘要

The half-Heusler compounds NiXSn (X = Ti, Zr, Hf) are regarded as examples of materials possessing excellent thermoelectric properties. We have studied their electronic structures by photoemission spectroscopy excited by soft and hard X-ray synchrotron radiation. Although the overall features of the experimental valence band spectra are well explained by a calculated density of states,"in-gap" states close to the Fermi energy emerge due to atomic disorder. These electronic states were further confirmed by core-level photoemission and appear to be key for excellent thermoelectric behavior.