  In this paper a comparative structural, dielectric and magnetic study of two
langasite compounds Ba$_3$TeCo$_3$P$_2$O$_{14}$ (absence of lone pair) and
Pb$_3$TeCo$_3$P$_2$O$_{14}$ (Pb$^{2+}$ 6$s^2$ lone pair) have been carried out
to precisely explore the development of room temperature spontaneous
polarization in presence of stereochemically active lone pair. In case of
Pb$_3$TeCo$_3$P$_2$O$_{14}$, mixing of both Pb 6$s$ with Pb 6$p$ and O 2$p$
help the lone pair to be stereochemically active. This stereochemically active
lone pair brings a large structural distortion within the unit cell and creates
a polar geometry, while Ba$_3$TeCo$_3$P$_2$O$_{14}$ compound remains in a
nonpolar structure due to the absence of any such effect. Consequently,
polarization measurement under varying electric field confirms room temperature
ferroelectricity for Pb$_3$TeCo$_3$P$_2$O$_{14}$, which was not the case of
Ba$_3$TeCo$_3$P$_2$O$_{14}$. Detailed study was carried out to understand the
microscopic mechanism of ferroelectricity which revealed the exciting
underlying activity of poler TeO$_6$ octahedral unit as well as Pb-hexagon.
