  We propose an inexpensive scalable approach for achieving extremely high
values of Seebeck coefficient ($\alpha$) by exploiting the natural superlattice
structure in Aurivillius phase oxides. In particular, we report an $\alpha
\approx $ 319\,mV/K at 300\,K in a composite of Aurivillius phase compound
SrBi$_4$Ti$_4$O$_{15}$ (as a matrix) and a perovskite phase material (e.g.,
La$_{0.7}$Sr$_{0.3}$MnO$_3$ or, La$_{0.7}$Sr$_{0.3}$CoO$_3$ as filler). Such a
colossal value of $\alpha$ can be attributed to contributions from the enhanced
density of states due to the effective low dimensional character of Bi$_2$O$_2$
layer. The corresponding thermal conductivity ($\kappa$) and the electrical
conductivity ($\sigma$) lies in the range 0.7 - 1.25 W/m-K and 10 - 100
$\mu$S/m, respectively at 300\,K. Attributed to the high $\alpha$ values, such
oxide composites can be used as thermopile sensors and highly sensitive
bolometric applications. We anticipate that the demonstration of colossal
$\alpha$ in oxide composites using a simple synthesis strategy also sets the
stage for future material innovations for high temperature thermoelectric
applications.
