Observation of Fano asymmetry in Raman spectra of SrTiO₃ and Cax Sr_1-xTiO₃ perovskite nanocubes

Bulk SrTi O3 is cubic and not expected to exhibit any first-order Raman scattering. However, nanocubes of SrTi O3 with an edge length of 80±10 nm show strong first-order Raman scattering originating from the breaking of symmetry caused by frozen surface dipoles (local tetragonality) and the presence of nanoscopic polar domains (arising from incorporated impurities). Rapid polarization fluctuations within these nanoscopic ferroelectric regions interfere with a polar phonon, resulting in a Fano-like asymmetric line shape in these SrTi O3 nanocubes, as well as in Ca0.3 Sr0.7 Ti O3 nanocubes.