Broad-Band Dielectric Spectroscopy of Relaxor Ferroelectric Sr_(0.61)Ba_(0.39)Nb_2O_6

摘要

Broad-frequency range dielectric data of strontium barium niobate with 61 percent of Si; from kHz to THz range, has been studied using various experimental techniques (FTIR, time-domain THz spectroscopy, HF coaxial technique and standard LF dielectric spectroscopy) in a wide interval of temperatures (20-600 K). Strong dielectric anisotropy was seen by all the experimental methods. Relaxor properties were detected in the epsilon_c~* response, where an intense relaxation slows down from the microwave range (T > T_m,) and broadens to low frequencies on cooling. The slowing down stops below MHz near 200 K. On further cooling it disappears gradually from the spectra leaving a constant loss background. The high-frequency wing of this relaxation is seen also in the THz range at high temperatures. IR modes show standard behaviour with decreasing temperature and no anomalies in phonon frequencies were observed. This brings evidence for the order-disorder type of the ferroelectric phase transition. Dielectric data perpendicular to the polar axis show anomalous features at low temperatures, but there is no sufficient evidence for another phase transition suggested by other authors below 100 K.