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Zusammenfassung:
Vibrational and elastic properties of the RFe4Sb12 skutterudites are investigated by, respectively, temperature (T) dependent extended x-ray absorption fine structure (EXAFS) and pressure (P) dependent x-ray diffraction (XRD) experiments. The Fe K-edge EXAFS experiments of the R=K, Ca, and Ba materials were performed in the T interval 6<T<300K and XRD experiments of the R= Na, K, Ca, Sr, and Ba materials were performed in the P interval 1atm<P<16GPa. From EXAFS, we obtained the correlated Debye-Waller parameters that were thus analyzed to extract effective spring constants connected with the Fe-Y (where Y= either R, Fe or Sb) scattering paths. Our findings suggest that in the case of the light cations, R=K or Ca, the R atoms are relatively weakly coupled to the cage, in a scenario reminiscent to the Einstein oscillators. From the XRD experiments, we obtained the bulk modulus B0 for all R=Na, K, Ca, Sr, and Ba materials, with values ranging from 77 GPa (R=K) to R=99GPa (R= Ba) as well as the compressibility β as a function of P. The trend in β as a function of the R filler is discussed and it is shown that it does not correlate with simple geometrical considerations but rather with the filler-cage bonding properties. © 2022 American Physical Society.
