Suppression of the gap energy in Zr-Ni-Sn and Ti-Ni-Sn by partial substitution of Zr and Ti by Ce

We report on magnetic measurements and electronic structure investigations of the alloyed compounds Zr-Ni-Sn and Ti-Ni-Sn. Both belong to the group of semi-Heusler alloys, and are classified as narrow-gap semiconductors with indirect gaps near 500 meV. Tetravalent ions (Zr,Ti) are partly replaced by Ce, with a Ce concentration less than 20%. Susceptibility measurements indicate the magnetic ground state of Ce in both Zr-Ni-Sn and Ti-Ni-Sn, and the effective moment is near the trivalent value at T=300K. The Ce 4f¹ configuration is well accepted by Ce $3d$ x-ray photoemission spectra. We compare the x-ray photoemission spectroscopy valence-band spectra for investigated Ce alloys. A very good agreement between the experiments and calculations is obtained. We classify Zr-Ni-Sn and Ti-Ni-Sn as alloys with a strong hybridization influence on the gap formation. The destructive alloying affecting the gap stability seems to have the same origin as in the case of Ce Kondo insulators.