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Abstract
Hyper-Raman scattering experiment has been performed in SrTi(18Ox 16O1-x)3 single crystal with exchange rate x = 0.87. A polar F1u Slater mode is detected in the cubic phase. This mode becomes an Eu mode in the tetragonal phase and softens toward the phase transition temperature Tc = 26 ± 3 K. Electric field induced light scattering experiment has also performed in SrTi(18Ox 16O1-x)3 single crystal with x = 0.96 under electric field of 120 kV/m. The softening behavior of the Eu mode (Raman-inactive mode) is observed clearly not only below Tc = 27 ± 1 K but also above Tc. However, the softening is confirmed to be incomplete (minimum frequency is about 200 GHz). These experimental facts strongly support the reported conclusion that the phase transition mechanism of SrTi(18Ox 16O1-x)3 is of displacive type (the instability of the Eu soft mode of Slater type causes the ferroelectric phase transition) but is not of ideal one.
Acknowledgments
The present work has been supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan, No. 14340086.