Phonon scattering rates and atomic ordering inAg1−xSb1+xTe2+x(

Abstract

The phonon dispersions and scattering rates of the thermoelectric material Ag1−xSb1+xTe2+x (x = 0, 0.1, 0.2) were measured with inelastic neutron scattering, as function of both temperature T and off-stoichiometry x. In addition, detailed measurements of diffuse scattering were performed with both neutron and synchrotron x-ray diffraction. The results show that phonon scattering rates are large and weakly dependent on T or x, and the lattice thermal conductivity calculated from these scattering rates and group velocities is in good agreement with bulk transport measurements. We also find that the scattering rates and their temperature dependence cannot be accounted for with common models of phonon scattering by anharmonicity or point defects. The diffuse scattering measurements show a pervasive, complex signal, with several distinct components. In particular, broad superstructure reflections indicate a short-range ordering of the Ag and Sb cations on their sublattice. Single-crystal Bragg peak intensities also reveal large static atomic displacements, compatible with results from Rietveld refinement of neutron powder diffraction data. Our results indicate that a complex nanostructure, arising from multiple variants of nanoscale anisotropic superstructures of cations, and large atomic displacements, is likely responsible for the strong phonon scattering.

Direct measurement of individual phonon lifetimes in the clathrate compound Ba7.81Ge40.67Au5.33

“…Our results are also compared in Fig. 5 to previously obtained data in other thermoelectrics such as PbTe 17 – 19 or AgSbTe 2 19 , 42 and amorphous Silica 46 – 48 . For the clathrate Ba 7.81 Ge 40.67 Au 5.33 and in the energy range 2–4 meV we find much larger lifetimes than in all these compounds.…”

“…The calculated phonon lifetime from DFT (see text) for the mode is shown as ( empty pink squares ). Previous experimental determination of acoustic phonon lifetimes in the same energy range are reported for PbTe ( full black squares , Delaire et al 17 ), AgSbTe 2 ( empty triangles , Ma et al 19 , 21 ) and amorphous Silica ( full black triangles , Baldi et al 48 ) …”

“…A typical inelastic neutron scattering (INS) experiment allows measuring lifetimes up to τ ~ 5 ps (corresponding to a phonon energy full-width at half maximum Γ FWHM ~ 250 µeV), which give a MFP of the order of 10 nm for a phonon group velocity of 2000 m.s −1 . As a result, effective phonon lifetimes have been accurately measured only in a few cases where they are already very short, such as in PbTe (Γ FWHM ~ 400 μeV, τ ~ 3 ps for E ~ 1.5 meV) 17 – 19 and Na 0.8 Co 2 (Γ FWHM ~ 625 μeV, τ ~ 2 ps) 20 or in nanostructured materials with nanometric grains such as AgSbTe (Γ FWHM ~ 500 μeV, τ ~ 2.6 ps for E ~ 1.5 meV) 19 , 21 . The neutron resonant spin-echo technique (NRSE) allows for accessing much longer lifetimes, but up to now it has been applied only to simple systems such as Pb and Nb, where lifetimes in the range 25–90 ps (Γ FWHM = 15−5 μeV) have been reported 22 .…”

Low-energy phonons and superconductivity inSn0.8In0.2Te

“…16,18,28,[36][37][38] Limited by the energy and Q range of our measurements, we are not able to map out the entire band for this TO mode. Nevertheless, we did look for the column type intensity in our SPINS measurements (Fig.…”

“…For the LA phonon mode, we see one high point for q = 0.07, while the product remains almost constant for all other q values. This high point at small q could be a possible result of the anomalously broad soft TO phonon mode near zone center 18,38 observed in PbTe and SnTe at low temperatures. The measured phonon energy and momentum widths are shown in the lower panels of Fig.…”