Precursory Softening of Polar Mode in Isotope-Exchanged Paraelectric Strontium Titanate Studied by Raman Scattering

Quantum paraelectric SrTiO₃ shows the ferroelectricity by the exchange of ¹⁶O for its isotope ¹⁸O. Raman scattering experiment is performed on the isotopically exchanged SrTi(O_0.32 ^{16 18}O_0.68)₃ whose exchange rate is just below the critical exchange rate. Raman spectrum of ferroelectric soft mode in the paraelectric phase clearly indicates local symmetry-breaking induced by the ¹⁸O-exchange. The temperature dependence of the soft mode in SrTi(O_0.32 ^{16 18}O_0.68)₃ suggests the occurrence of local ferroelectric region before the onset of the ferroelectric phase. The inhomogeneity of the system induces the inhomogeneous softening of the soft mode in ¹⁸O-exchanged SrTiO₃.

Keywords:

• Quantum paraelectric
• strontium titanate
• isotope and light scattering

Acknowledgment

The present study is partially supported by a Grant-in-Aid for JSPS Fellows, a Grant-in-Aid for Scientific Research (A) from JSPS No. 14204029, and a Grant-in-Aid for Young Scientists (A) from MEXT No. 14702006.

Paper originally presented at IMF-11, Iguassu Falls, Brazil, September 5–9, 2005