E. Bauer¹, St. Berger¹, G. Hilscher¹, H. Michor¹, Ch. Paul¹, M. Reissner¹, A. Grytsiv², P. Rogl²

Filled skutterudites based on Pr are known to exhibit a number of extraordinary ground state properties like superconductivity, heavy fermion superconductivity, metal to insulator transition, ordering due to quadrupolar contributions or due to standard RKKY interaction of the 4f² electrons. Pr_0.73Fe₄Sb₁₂ orders magnetically at T_mag = 4.6 K. An effective magnetic moment µ_eff = 4.19 µ_B indicates that [Fe₄Sb₁₂] carries an effective magnetic moment of 2.7 µ_B. Ground-state properties of Pr_0.73Fe₄Sb₁₂ are primarily governed by crystal field splitting and Kondo like interaction causes a significant enhancement of the Sommerfeld value of the specific heat.

We present a thorough investigation of Pr_0.73Fe₄Sb₁₂ by means of magnetic and thermodynamic measurements, by transport coefficients studied as a functions of temperature, magnetic field and hydrostatic pressure as well as by Moessbauer spectroscopy. We will show how the strong electron correlations at low temperatures influence thermopower and how this correlations evolve under substitutions on both the transition element and the pnicogen site. Such substitutions drive an enhancement of thermopower by more than a factor of 2, reaching values of about 240 µV/K in the case of Pr_0.2Fe_2.5Ni_1.5Sb₁₂ and about –100 µV/K for Pr_0.25FeCo₃Sb₁₂. Substitutions in this series of compounds originate additionally a metal to insulator transition.