Band gap stability in Kondo insulators

We report on magnetic measurements and electronic structure investigations of CeNiSn and CeRhSb. Both belong to the group of Kondo insulators. The mag netic susceptibility shows the nonmagnetic ground state for these compounds and their alloys. The 3d X-ray photoemission spectroscopy spectra show evi dence for the mixed valence state of Ce in CeRhSb alloys, as also seen for CeNiSn, whereas the spectra for the La substituted (Ce,La)NiSn compounds sh ow only evidence for a pure Ce3+ ground state. We suggest the presence of K ondo-hole states in (Ce,La)RhSb. The location of the pseudogap in CeRhSb va ries with the number of free electron, the valence of Ce, and the f-d hybri dization. We discuss the similar crystallographic proper ties and the close d electronic structures of ZrNiSn-type semi-Heusler alloys and CeNiSn-type Kondo insulators.