Ground state properties and thermoelectric behavior of PrFe4-xTMxSb12-ySny (TM = Co, Ni)

Quasi ternary filled skutterudites Pr_y(Fe,Co,Ni)₄(Sb,Sn)₁₂ were investigated by means of temperature dependent magnetization -, specific heat -, electrical resistivity - and thermopower measurements. As non-Kramers ion in cubic environment Pr can exist in both a magnetic or a nonmagnetic ground state and crystal field effects strongly influence physical properties in an extended temperature range. Detailed investigations of Pr_0.73Fe₄Sb₁₂ point to antiferromagnetic order and Γ₅ as crystal field ground state. Strong electron correlations give rise to significantly enhanced masses of charge carriers, which in turn enhances the Seebeck coefficient S(T). Owing to the Fe/Ni substitution, large values of S(T) are found reaching figures of about 230 μV/K at 425 K for Pr_0.21Fe_2.5Ni_1.5Sb₁₂ in combination with low thermal conductivity as expected for this class of materials. Moreover, the Fe/Ni substitution drives the system from hole- to electron-dominated transport, which is obvious considering the crossover of S(T) from positive to negative thermopower values in Pr_0.1Fe₂Ni₂Sb₁₂.