Three-phonon scattering processes and thermal conductivity in IV-chalocogenides
, Jawaher Al-Otaibi . 2015
We present a systematic study of allowed three-phonon scattering processes, involving acoustic and optical branches, and their relative roles in explaining the low thermal conductivity 
of IV-chalcogenide thermoelectric materials PbTe, PbSe, PbS, and SnTe. Using numerical results for 
, computed by employing the isotropic continuum scheme, we have examined the extent of the additional contribution the Callaway theory and the Allen theory provide over the single-mode relaxation time theory. Within the Callaway theory, for all these materials the acoustic (
, 
) and transverse optical (
) phonons contribute between 10–25% towards 
at and above room temperature, with 
. The longitudinal optical (
) phonons contribute negligibly (<5%) in Pb-chalogenides, but their contribution is larger (22%) than that of 
phonons (18%) in SnTe. Due to the presence of high defect concentration in these materials, the high temperature conductivity varies less strongly than T−1. In confirmation with experimental measurements, our study finds that below the Debye temperature the resistivity of SnTe varies as the square-root of the point defect concentration.
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We present a systematic study of allowed three-phonon scattering processes, involving acoustic and optical branches, and their relative roles in explaining the low thermal conductivity …