  We present temperature dependent frequency shift and line broadening of
phonon modes by insertion of atomic layers of Pb and PbTe in the prototype 3D
topological insulator Bi2Te3, using Raman spectroscopy. Good quality single
crystals of Pb2Bi2Te3, PbBi2Te4 and PbBi4Te7 are grown using the modified
Bridgman technique. The Raman modes show progressive blue shift with the
decrease in temperature from 298 K to 93 K in Pb2Bi2Te3, PbBi2Te4 and PbBi4Te7
is due to anharmonic vibrations of the lattice as well as increasing strength
of Bi-Te covalent interactions. Experimental results are complemented by
extensive density functional theory calculations where a reasonable matching
between experimental and computational data is found. Chemical pressure,
induces by the insertion of Pb and PbTe layers in Bi2Te3, modifies the
interactions at the boundaries of the quintuple-layers which is evident from
the evolution of mode. The enhancement of out-of-plane Bi-Te vibrations with
respect to in-plane Bi-Te vibrations are observed at low temperatures.
