Elastic properties of filled-Skutterudite compounds probed by Mössbauer nuclei

Abstract

We have carried out Mössbauer spectroscopy and nuclear resonant inelastic scattering to elucidate the lattice dynamics in filled-Skutterudite compounds, especially phosphides. The second-order Doppler shift obeys the Debye model in RFe 4 P 12 . Nuclear quadrupole interaction reveals an unusual temperature dependence in these compounds. An anomaly is observed in 57 Fe nuclear resonant inelastic scattering of these compounds. The energy where the anomaly observed in SmFe 4 P 12 agrees with the phonon excitation energy observed by 149 Sm nuclear resonant inelastic scattering. We have also performed the 99 Ru Mössbauer measurements of SmRu 4 P 12 .

149Sm and 57Fe nuclear resonant inelastic scattering of filled skutterudites SmFe4X12 (X: pnictogen)

“…All the spectra obtained exhibit relatively sharp excitation, suggesting the presence of a dispersionless mode similar to an Einstein mode. Similar spectra have already been reported for other filled skutterudites [4,9]. The excitation energy decreases with increasing ionic radius of X, whereas the line width increases with increasing X ionic radius.…”

“…As was reported Ref. [9], a dip structure was found in the 57 Fe NRIS spectrum of SmFe 4 P 12 in spite of the inferior energy resolution of 3.5 meV. The energy at which the dip structure was found is in good agreement with that of Sm phonon excitation observed by 149 Sm NRIS, although the Sm phonon energy is slightly shifted, mainly due to the shirinkage of the unit cell volume with decreasing temperature [13].…”

149Sm nuclear resonant inelastic scattering of SmB6

“…This demonstrates the presence of the dispersionless modes, as was indicated by the inelastic neutron scattering [13]. This is similar to Sm filled skutterudites [14,15]. Assuming the Gaussian-shaped partial DOS, the obtained spectrum is well reproduced with multiple phonon contributions [16].…”

Atomic dynamics of low-lying rare-earth guest modes in heavy fermion filled skutteruditesROs4Sb12(Tsutsui1, Uchiyama2, Sutter3 et al. 2012Phys. Rev. B262100View full textAdd to dashboardCite

“…For the filled skutterudites, observations of low-lying dispersionless modes below ∼10 meV in inelastic neutron and x-ray scattering experiments [10][11][12][13][14][15][16][17] and those of Einstein temperatures below ∼100 K in specific heat, x-ray diffraction, extended x-ray absorption fine structure (EXAFS), and nuclear magnetic resonance (NMR)/nuclear quadrupole 13 44 resonance (NQR) experiments have been reported. [18][19][20][21][22][23][24][25] At the beginning of the investigation of low-lying optical modes in filled skutterudites, 6,10,12,[26][27][28] which are called guest modes hereafter, it was discussed whether or not the guest modes were localized. This means that the presence of an Einstein-like localized mode is important in proving the validity of the PGEC model.…”