Ground state properties and thermoelectric behaviour of PrFe4-xTMxSb12-ySny (TM = Co, Ni)
E. Bauer1, St. Berger1, G. Hilscher1, H. Michor1, Ch. Paul1, M. Reissner1, A. Grytsiv2, P. Rogl2
1Institut für Festkörperphysik, T.U. Wien, Wiedner Hauptstraße 8-10 A-1040 Wien, Austria
2Institut für Physikalische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien, Austria
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. Pr0.73Fe4Sb12 orders magnetically at Tmag = 4.6 K. An effective magnetic moment µeff = 4.19 µB indicates that [Fe4Sb12] carries an effective magnetic moment of 2.7 µB. Ground-state properties of Pr0.73Fe4Sb12 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 Pr0.73Fe4Sb12 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 Pr0.2Fe2.5Ni1.5Sb12 and about –100 µV/K for Pr0.25FeCo3Sb12. Substitutions in this series of compounds originate additionally a metal to insulator transition.