Semiconducting behaviour of Ce₃ Cu₃ Sb₄ revisited

We present the studies involving band structure calculations and experimental characterization of Ce₃ Cu₃ Sb₄ compound, as well as the Ce₃ Cu_3−x Ni_xSb₄ series where Cu atom was substituted by its neighbour Ni in periodic system. Ce₃ Cu₃ Sb₄ was previously reported as ferromagnetic semiconductor or semimetal with significant thermopower at room temperature. Basing on our calculations, we show that it has some residual density of states at the Fermi level and relatively broad band gap just below Fermi level. We present calculations performed within virtual crystal approximation which simulate the doping and the vacancies as well as the calculations for the reduced unit cell which simulate the effect of hydrostatic pressure onto the bandgap in the density of states. We show that 4f electron correlations have tremendous influence on the shape and location of band-gap. The calculations also show the shift of the bandgap in respect to the Fermi level as a result of external pressure or change of the stoichiometry. In consequence of the change of these parameters, Ce₃ Cu₃ Sb₄ would became a unique wide bandgap Ce based semiconductor. We also present thermopower, thermal conductivity, resistivity, Hall effect, and magnetic results obtained for the system Ce₃ Cu_3−x Ni_xSb₄. Thermoelectric figure of merit reaches value ZT ≈0.3 at 350 K for Ce₃ Cu_2.75 Ni_0.25 Sb₄, which qualifies these materials for thermoelectric applications. - Highlights: • Broad band gap near Fermi level. • Complicated magnetic properties. • Role of 4f-electron correlations. • Significant thermoelectric Figure of Merit.