  Systematic experimental and theoretical research on the role of
microstructure and interface thermal resistance on the thermal conductivity of
the PbTe-CoSb3 bulk polycrystalline composite is presented. In particular, the
correlation between the particle size of the dispersed phase and interface
thermal resistance (R_{int}) on the phonon thermal conductivity (\kappa_{ph})
is discussed. With this aim, a series of PbTe-CoSb_3 polycrystalline composite
materials with the different particle sizes of CoSb_3 was prepared. The
structural (XRD) and microstructural analysis (SEM/EDXS) confirmed assumed
chemical and phase compositions. The acoustic impedance difference (\Delta Z)
was determined from measured sound velocities in PbTe and CoSb_3 phases. The
interface thermal resistance (R_{int}) was calculated using the Debye model and
agrees with the experimental R_{int}. It is shown that the \kappa_{ph} of the
composite may be reduced when the particle size of the dispersed phase (CoSb_3)
is smaller than the critical value of ~230nm. This relationship was concluded
to be crucial for controlling the heat transport phenomena in composite
thermoelectric materials. The selection of the components with different
elastic properties (acoustic impedance) and particle size smaller than the
Kapitza radius leads to a new direction in the engineering of composite TE
materials with designed thermal properties
