Heavy fermion behavior in Pr0.5Ir4Sb10.2Sn1.8
Introduction
Filled skutterudites have attracted a great deal of interest for both their fundamental properties and potential applications. They exhibit a variety of interesting behaviors, including heavy fermion states [[1], [2], [3], [4]], anti-ferroquadrupolar order [5,6], non-Fermi liquid states [7,8], metal insulator transitions [9,10], and BCS [11,12] and exotic [13,14] superconductivity.
For thermoelectric applications, atoms in the voids of the skutterudite structure result in anharmonic vibrations with Einstein-like modes which can effectively scatter phonons [15]. This scattering does not substantially reduce the electrical conductivity, leading to a better thermoelectric figure of merit.
Pr filled skutterudites in particular have a variety of interesting ground states; For instance, PrFe4P12 shows a metal-insulator transition with anti-ferroquadrupolar ordering below the transition [16]. PrFe4As12 orders ferromagnetically at low temperatures [17], while PrRu4As12 is suggested to be an s-wave superconductor [18]. Perhaps the most interesting is PrOs4Sb12, an unconventional heavy fermion superconductor in which the pairing is thought to be odd parity and mediated by quadrupole fluctuations [19,20], which may host three dimensional Majorana fermions [21].
The large number of interesting behaviors for filled skutterudites has prompted attempts at synthesizing new compounds within this structural family. Luo et al. [22] looked at Group 9 skutterudites based on Co, Ru, and Ir. They showed that the filled skutterudites in these systems follow Zintl rules for formation, and by altering the atoms involved but keeping close to the same valence electron count (96), they were able to create more than 60 new compounds with hundreds more potentially possible. Based on electron counting rules, most of these materials should be close to a semiconducting state. The Ir members of this group are particularly interesting, since the large Z of Ir results in a strong spin-orbit coupling. By following these rules, partially filled skutterudites can also be created. Two of the compounds they synthesized in powder form were PrIr4Sb8Sn4 and Pr0.9Ir4Sb10.2Sn1.8.
Here we report the creation and characterization of single crystal samples of Pr0.5Ir4Sb10.2Sn1.8. We determined the crystal structure and relative composition through powder x-ray diffraction (PXRD) and energy dispersive x-ray spectroscopy (EDS), and found interesting low temperature behavior through specific heat, magnetization and electronic transport measurements. This material displays Kondo-alloy and heavy fermion behavior.
Section snippets
Methods
We synthesized single crystal Pr0.5Ir4Sb10.2Sn1.8 using the self-flux method following Bauer et al. [13]. Praseodymium (ingot, 3 N), iridium (powder, 4 N), antimony (shot, 5 N) and tin (shot, 4 N) were weighed (atomic ratios 1:4:13.33:6.66) and then sealed in carbon coated quartz ampoules which had been evacuated and then filled with 500 millitorr of argon gas. The samples were grown in the temperature range of to with a cooling rate and were then placed in a centrifuge at
Crystallography and composition
Fig. 1 shows the PXRD pattern and Rietveld refinement of a powdered single crystal Pr0.5Ir4Sb10.2Sn1.8 sample. The peaks are well indexed by the LaFe4P12 type cubic structure with space group Im-3 (#204). There is one very small peak of impurity phase at which was unidentifiable, however did not consist of any elements or compounds which may have come from the crystal growth process. The refined lattice parameter is found to be . This is comparable to the value given by Ref. [22]
Conclusions
In conclusion, we have grown the first single crystal samples of Pr0.5Ir4Sb10.2Sn1.8. This material shows heavy fermion behavior and Kondo like scattering. The large negative Curie temperature [] implies antiferromagnetic correlations and a Kondo temperature . From the specific heat we find an enhanced electronic coefficient , which is on the lower extreme of a heavy fermion compound. The value for , along with the coefficient extracted from the
CRediT authorship contribution statement
Matthew S. Cook: Investigation, Formal analysis, Visualization, Writing - original draft. Clement A. Burns: Conceptualization, Methodology, Investigation, Validation, Writing - review & editing, Supervision, Funding acquisition.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We would like to thank Dr. Pnina Ari-Gur, Department of Mechanical and Aerospace Engineering, Western Michigan University for use of the PANalytical PXRD facility which was funded by National Science Foundation, United States MRI Award 1626276. This work was partially funded by Michigan Space Grant Consortium, NASA grant #NNX15AJ20H. The PPMS used for measurements was funded by NSF MRI grant 1828387.
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