[13p-2L-1~11] 9.1 Dielectrics, ferroelectrics

▲ [13p-2L-10] Electric field effect on ferroelectric phase transition of Li-doped KTa_1-xNb_xO₃ single crystals studied by Brillouin scattering

〇(D)Md. Mijanur Rahaman¹, Tadayuki Imai², Junya Kobayashi², Seiji Kojima¹ (1.Univ. Tsukuba, 2.NTT Photonics Labs)

Keywords:Phase transition,Critical end point,Brillouin scattering

Electric field effect on the ferroelectric phase transition of Li-doped KTN single crystals was investigated by Brillouin scattering and dielectric measurements. The remarkable changes of the central peak (CP) intensity were observed, indicating the paraelectric cubic to ferroelectric tetragonal phase transition. However, the frequency of transverse acoustic (TA) phonon began to soften at the critical electric fields. The critical electric fields to induce the paraelectric to ferroelectric phase transition were found to shift to higher values with increasing temperature. From these CP results, we estimated lines of critical points for phase transitions including CEP, (E, T) = (1.6 kV/cm, T_C+3.4 ºC) in the composition-temperature-electric field (x-T-E) phase diagram. At the electric fields, E_C1 and E_C2, the ferroelectric to paraelectric phase transition on cooling and the paraelectric to ferroelectric phase transition on heating occurred, respectively. The field effect of dielectric properties was also studied.