  It is thought that the proposed new family of multi-functional materials
namely the ferroelectric thermoelectrics may exhibit enhanced functionalities
due to the coupling of the thermoelectric parameters with ferroelectric
polarization in solids. Therefore, the ferroelectric thermoelectrics are
expected to be of immense technological and fundamental significance. As a
first step towards this direction, it is most important to identify the
existing high performance thermoelectric materials exhibiting ferroelectricity.
Herein, through the direct measurement of local polarization switching we show
that the recently discovered thermoelectric semiconductor $AgSbSe_{2}$ has
local ferroelectric ordering. Using piezo-response force microscopy, we
demonstrate the existence of nanometer scale ferroelectric domains that can be
switched by external electric field. These observations are intriguing as
$AgSbSe_{2}$ crystalizes in cubic rock salt structure with centro-symmetric
space group (Fm-3m) and therefore no ferroelectricity is expected. However,
from high resolution transmission electron microscopy (HRTEM) measurement we
found the evidence of local superstructure formation which, we believe, leads
to local distortion of the centro-symmetric arrangement in $AgSbSe_{2}$ and
gives rise to the observed ferroelectricity. Stereochemically active $5s^{2}$
lone pair of Sb can also give rise to local structural distortion, which
creates ferroelectricity in $AgSbSe_{2}$.
