  In this study, the synergistic effect of the particle size of the dispersed
phase and the interface thermal resistance (R$_{int}$) between the phases on
the phonon thermal conductivity ($\kappa_{ph}$) of the
(1-x)La$_{0.95}$Sr$_{0.05}$Co$_{0.95}$Mn$_{0.05}$O$_3$/(x)WC thermoelectric
composite, is demonstrated. Further, the correlation between the R$_{int}$ and
the Kapitza radius is discussed using the Bruggeman's asymmetrical model. In
particular, the polycrystalline
La$_{0.95}$Sr$_{0.05}$Co$_{0.95}$Mn$_{0.05}$O$_3$ sample is synthesized using a
standard-solid state route. The presence of WC nanoparticle is confirmed from
the electron microscopy images. Electrical conductivity ($\sigma$) increases,
and the Seebeck coefficient ($\alpha$) decreases with the increase in
conducting WC volume fraction in the composite. The simultaneous increase in
$\sigma$ and a decrease in $\kappa_{ph}$ with the WC volume fraction results in
an increased figure of merit (zT) for
(1-x)La$_{0.95}$Sr$_{0.05}$Co$_{0.95}$Mn$_{0.05}$O$_3$/(x)WC composite. A
maximum zT $\sim$ 0.20 is obtained for
(1-x)La$_{0.95}$Sr$_{0.05}$Co$_{0.95}$Mn$_{0.05}$O$_3$/(x)WC composite for
x=0.010 at 463 K. The results obtained in the present study shows promise to
design thermoelectric composites with desired phonon thermal conductivity
considering the elastic properties between the phases.
