Observation of Fano asymmetry in Raman spectra of SrTiO_3 and Ca_xSr_(1-x)TiO_3 perovskite nanocubes

摘要

Bulk SrTiO_3 is cubic and not expected to exhibit any first-order Raman scattering. However, nanocubes of SrTiO_3 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 SrTiO_3 nanocubes, as well as in Ca_(0.3)Sr_(0.7)TiO_3 nanocubes.