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Abstract

Boron-rich materials combine chemical stability with refractory properties and, consequently, are interesting for high-temperature thermoelectric applications. Therefore, the magnetic, electrical, and thermal transport properties of the Y1-xCexCrB4 series have been investigated here to employ the concept of correlation-enhanced thermoelectric properties. Combining X-ray diffraction and energy-or wavelength-dispersive spectrometry, we find a rather narrow stability range of Y1-xCexCrB4, only samples on the Y- A nd Ce-rich substitution limits (x=0,0.05,0.95,and1) were obtained. Electrical resistivity data show a change from semiconducting (x=0) to metallic behavior upon Ce substitution (x≥0.95). From magnetic susceptibility measurements and X-ray absorption spectroscopy, we find a temperature-dependent intermediate valence state of Ce of about +3.5. However, a fit of the magnetic susceptibility data to the Coqblin-Schrieffer model yields a surprisingly high Kondo temperature of about 1100 K. Together with the good thermal conductivity for the studied substitution series this impedes a suitable thermoelectric performance. Electronic structure calculations for YCrB4 support its narrow gap semiconducting nature in contrast to previous studies. Surprisingly, its electronic structure is characterized by pronounced van Hove singularities very close to the Fermi-level EF. They originate from nearly dispersionless Cr 3dz2-r2-derived bands in a large part of the Brillouin zone, suggesting the appearance of electronic instabilities upon rather small electron doping into these states. © 2021 American Physical Society.