Using
a set of controlled in situ grown lamellar composites of
(Cu2Te)62.02–(Sb2Te3)37.98, we report a remarkable variation of transport
properties of thermoelectricity not only as a function of microstructural
length scale but also as a function of direction-dependent arrangement
of the phases and hence their interfaces. A quantitative evaluation
of the microstructure along the transverse and the longitudinal directions
of growth, imposed by the temperature gradient and growth rate in
a unidirectional solidification setup, has been carried out. The microstructure
is quantified through image analysis using fast Fourier transforms
as well as a cluster base connectivity model and is further correlated
with the thermoelectric transport properties. A marked anisotropy
of properties as a function of measurement direction in the microstructural
landscape could be observed. A maximum power factor of ∼1.4
mW m–1 K–2 and a figure of merit
of 0.29 could be obtained at 580 K along the transverse direction
for the sample with the characteristic microstructural length scale
of 2.41 μm. This has an implication in engineering a thermoelectric
device in terms of engineering power factor and output power density.
For a ΔT of 250 K, we report a difference of
0.4 W cm–2 in output power density between the transverse
and the longitudinal directions that have an identical microstructural
length scale of 2.41 μm.
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