Crystal structure, 139La NMR and transport properties of the As-based filled skutterudites LaOs4As12 and PrOs4As12
Introduction
The filled skutterudite compounds, which have the formula AT4X12 (A = alkali metal, alkaline earth, lanthanide or actinide; T = Fe, Ru, or Os; and X = P, As, or Sb), display a wide variety of strongly correlated electron phenomena. Very recently, we reported that PrOs4As12 displays two ordered phases below ∼2.3 K for magnetic fields less than 3 T. Neutron-scattering experiments in zero field established an antiferromagnetic (AFM) ground state at T < 2.28 K [1], [2]. The temperature and magnetic field dependence of the electrical resistivity and the specific heat in the paramagnetic state are consistent with a single-ion Kondo behaviour with a characteristic temperature of the order of ∼1 K. For better understanding the influence of 4f electrons on the physical properties of PrOs4As12, we have performed studies of its non-4f electron homologue LaOs4As12 by means of the X-ray diffraction, 139La NMR, dc magnetic susceptibility and thermoelectric power.
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Experimental details
Single crystals of LaOs4As12 and PrOs4As12 were grown from elements with purities better than 99.9% by a molten metal flux method at high temperatures and pressures. Details of the crystal structure determination of PrOs4As12 are given in [1]. The crystal structure of LaOs4As12 was determined by X-ray diffraction on a specimen with dimensions of 0.21 mm × 0.21 mm × 0.24 mm. The structure was resolved by using the SHELX-97 program with a final discrepancy factor R1 = 0.0319 [for I > 2σ(I), R2 = 0.0855] [3],
Results and discussion
Single crystal structural refinement shows that LaOs4As12 and PrOs4As12 have the LaFe4P12-type structure (Im space group) with two formula units per unit cell, and lattice parameters of 8.542(1) Å and 8.520(1) Å, respectively. The lanthanide (Ln) ion is located inside an icosahedron formed by the 12 As anion neighbours closest to Ln with Ln–As distances equal to 3.2466(13) Å and 3.2270(7) Å for La and Pr, respectively. On the other hand, the Os ion is situated inside an octahedron formed by the 6
Acknowledgements
Research at UCSD was supported by the U.S. Department of Energy under Grant No. ∼DE-FG02-04ER46105 and the U.S. National Science Foundation under Grant No. ∼DMR 0335173. T.Y. was supported by a JSPS Postdoctoral Fellowship for Research Abroad.
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