Effect of Oxygen Isotope Exchange on Ferroelectric Microregion in SrTiO_3 Studied by Raman Scattering(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

概要

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The ferroelectric microregion (FMR) in quantum paraelectric SrTiO_3 is studied by Raman scattering using an optical cryostat with a ^3He refrigerator. By the partial exchange of the oxygen atom for its isotope ^<18>O, broad FMR spectra change drastically to underdamped Lorentzian-type spectra with decreasing temperature below 10 K. The peak is assigned to the ferroelectric soft Eu mode. The intense and sharp spectra of the Eu mode, which are nominally Raman inactive, indicate that the symmetry is lowered to a non-centrosymmetnc symmetry in FMR Furthermore, the softening characteristic of the soft Eu mode in a low-temperature region implies that the symmetry is not necessarily ferroelectric The local symmetry breaking is enhanced by the substitution of the isotope ^<18>O.
社団法人日本物理学会の論文
2004-12-15