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The scattering of thermal acoustic phonons by point defects in solids has been widely assumed the Rayleigh scattering type. In contrast to this conventional perception, using an ab initio Green's function approach, we show that the scattering by point defects in PbTe and GeTe exhibits Mie scattering characterized by a weaker frequency dependence of the scattering rates and highly asymmetric scattering phase functions. These unusual behaviors occur because the strain field induced by a point defect can extend for a long distance up to 10 Å. Because of the asymmetric scattering phase functions, the widely used relaxation time approximation fails with an error of ~20% at 300K in predicting lattice thermal conductivity when the vacancy fraction is 1%. Our results show that the phonon scattering by point defects in IV-VI semiconductors cannot be described by the simple kinetic theory combined with Rayleigh scattering.3 Scattering of waves by the inhomogeneity of the medium is a fundamental process underpinning diverse applications including electromagnetics, optics, and acoustics [1][2][3][4]. This is of equal importance for thermal phonons [5][6][7]. Randomly distributed particles can result in phonon localization through multiple scattering and interference of phonon waves [8,9]. Periodic inclusions in phononic crystals give rise to new vibrational band structures due to Bragg and Mie scatterings [10,11]. The wave-defect interaction is usually assumed elastic and its characteristics dramatically depend on the size of the scattering centers. The elastic scattering of phonons, analogous to that of electromagnetic waves, falls into three regimes: (i) Rayleigh scattering for the scattering centers much smaller than the phonon wavelength (where d and  are the diameter of the scattering center and the wavelength, respectively), (ii) Mie scattering for those with comparable size to the wavelength ( 1/10 d  ), and (iii) Geometric scattering for those larger than the wavelength ( d   ) [12,13].A point defect at a single lattice site possesses the minimum size of a scattering center in solids. Since the wavelengths of thermal phonons are usually many times of the lattice spacing, the scattering of thermal phonons by a point defect is often considered as Rayleigh scattering and exhibits very weak scattering strength for low frequency phonons.The Rayleigh scattering is well captured by models suggested by Klemens [14] and Tamura [15], which assume that the change in mass and interatomic force constants (IFCs) by a point defect is limited to a single lattice site. The recently developed ab initio Green's function approach [16,17] also shows the Rayleigh scattering behavior for strongly bonded materials, such as diamond and BAs [18][19][20][21][22][23][24].In this report, we show that the point defects in IV-VI semiconductors (PbTe and GeTe), unlike the previously studied strongly bonded materials, cause Mie scattering of thermal phonons. The IV-VI semiconductors are widely used for the applications of thermoelectrics an...

With the exception of consistent inverse association of CRP with total n-6 FAs, there are considerable variations across the three populations in the associations of CRP with different FAs.

With the exception of consistent inverse association of CRP with total n-6 FAs, there are considerable variations across the three populations in the associations of CRP with different FAs.