Nonlinear Dielectric Susceptibilities of Sr_<0.61>Ba_<0.39>Nb_2O_6 Relaxor Single Crystals

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Linear and nonlinear dielectric susceptibilities of Sr_<0.6>Ba_<0.39>Nb_2O_6 (SBN61) single crystals were measured along the polar c-axis. Both the linear and higher-order nonlinear dielectric responses showed significant frequency dispersion near the transition temperature (T_c), which signified the relaxor behavior in this system. The temperature dependence of the dielectric nonlinearity α_3 = X3/X_1^4 was obtained, which showed a dip slightly above T_c This fact seems to reflect the growth of polar nanoregions into long-range polar domains at around and below T_c. The second-harmonic nonlinear dielectric susceptibility showed significant values above T_c in the paraelectric regime, where the point group is 4/mmm with an inversion symmetry. We attributed this observation to the existence of polar clusters with broken inversion symmetry, which may be the remnants of long-range order above T_c due to the quenched random fields. This result is consistent with the suggestions made based on the linear birefringence, the strain and the second-harmonic generation measurements.
社団法人応用物理学会の論文
2002-11-30