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Register a new userEinstein Modes in the Phonon Density of States of the Single-Filled Skutterudite Yb$_{0.2}$Co$_{4}$Sb$_{12}$
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Measurements of the phonon density of states by inelastic neutron emph{time-of-flight} scattering and specific heat measurements along with first principles calculations, provide compelling evidence for the existence of an Einstein oscillator (emph{rattler}) at ${omega}_{E1} approx$ 5.0 meV in the filled skutterudite Yb$_{0.2}$Co$_{4}$Sb$_{12}$. Multiple dispersionless modes in the measured density of states of Yb$_{0.2}$Co$_{4}$Sb$_{12}$ at intermediate transfer energies (14 meV $leq$ emph{$omega$} $leq$ 20 meV) are exhibited in both the experimental and theoretical emph{density-of-states} of the Yb-filled specimen. A peak at 12.4 meV is shown to coincide with a second Einstein mode at emph{$omega_{E2} approx$} 12.8 meV obtained from heat capacity data. The local modes at intermediate transfer energies are attributed to altered properties of the host CoSb$_{3}$ cage as a result of Yb-filling. It is suggested that these modes are owed to a complementary mechanism for the scattering of heat-carrying phonons in addition to the mode observed at ${omega}_{E1} , approx$ 5.0 meV. Our observations offer a plausible explanation for the significantly-higher textit{dimensionless figures of merit} of filled skutterudites, compared to their parent compounds.
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A filled skutterudite, La$_{0.5}$Rh$_4$Sb$_{12}$, with a lattice constant of 9.284(2) {AA} was synthesized using a high-pressure technique. The electrical resistivity showed semiconducting behavior and the energy gap was estimated to be more than 0.08 eV. Magnetic susceptibility measurements indicated temperature-independent diamagnetism, which originates from Larmor diamagnetism. The electrical properties of this compound are more similar to those of the La$_{0.5}$Rh$_4$As$_{12}$ semiconductor with an energy gap of 0.03 eV than to those of the La$_{0.6}$Rh$_4$P$_{12}$ superconductor.
We report a study of the superconducting and normal-state properties of the filled-skutterudite system PrPt$_{4}$Ge$_{12-x}$Sb$_x$. Polycrystalline samples with Sb concentrations up to $x =$ 5 were synthesized and investigated by means of x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements. We observed a suppression of superconductivity with increasing Sb substitution up to $x =$ 4, above which, no signature of superconductivity was observed down to 140 mK. The Sommerfeld coefficient, $gamma$, of superconducting specimens decreases with increasing $x$ up to $x =$ 3, suggesting that superconductivity may depend on the density of electronic states in this system. The specific heat for $x =$ 0.5 exhibits an exponential temperature dependence in the superconducting state, reminiscent of a nodeless superconducting energy gap. We observed evidence for a weak rattling mode associated with the Pr ions, characterized by an Einstein temperature $Theta_{mathrm{E}} sim$ 60 K for 0 $leq x leq$ 5; however, the rattling mode may not play any role in suppressing superconductivity.
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