Observation of Fano asymmetry in Raman spectra of SrTiO3 and CaxSr1−xTiO3 perovskite nanocubes

Abstract

Bulk $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ is cubic and not expected to exhibit any first-order Raman scattering. However, nanocubes of $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ with an edge length of $80\pm 10\mathrm{nm}$ 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 $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ nanocubes, as well as in ${\mathrm{Ca}}_{0.3}{\mathrm{Sr}}_{0.7}\mathrm{Ti}{\mathrm{O}}_3$ nanocubes.