I have encountered the splitting of Raman bands (especially G band in G+ and G- peaks) while characterizing graphene under strain using Raman spectroscopy.
ATiO3-type materials may exist in two different crystalline forms: the perovskite and ilmenite. While many papers have devoted their attention to evaluating the structural properties of the perovskite phase, the structural stability of the ilmenite one still remains unsolved. Here, we present our results based on the lattice dynamics and first-principles calculations (density functional theory) of the CdTiO3 ilmenite phase, which are confronted with experimental data obtained through micro Raman spectroscopy that is a very good tool to probe the local crystal structure. Additional Raman bands, which are not foreseen from group-theory for the ilmenite rhombohedral structure, appeared in both low temperature (under vacuum condition) and high-pressure (at room temperature) spectra
"When the bond lengths and angles of graphene are modified by strain, the hexagonal symmetry of graphene is broken, and this symmetry breaking effects splits the LO and iTO mode frequencies."
You can find the above sentence in p. 163 of "Raman Spectroscopy in Graphene Related Systems".