Broad-Band Dielectric Spectroscopy of Relaxor Ferroelectric Sr_0.61Ba_0.39Nb₂O₆

Abstract

Broad-frequency range dielectric data of strontium barium niobate with 61% of Sr, 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 ε * 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.

Infrared and dielectric spectroscopy of the relaxor ferroelectric Sr0.61Ba0.39Nb2O6

“…Phonon anomalies were seen below 100 K, related to a possible new PT [13]. The IR reflectivity spectrum of SBN-61 (doped with Cu) was studied at room temperature in [14], and a preliminary temperature dependence for IR active modes along the polar axis was reported recently by us [15]. The presence of central peaks at very high temperatures was studied by means of Brillouin scattering [16]; this indicated a thermal switching of polar nanoclusters.…”

Proton conductors and their applications: A tentative historical overview of the early researches

“…Measurements in the 500 MHz-50 GHz require the use of many microwave sources, guide/coaxial cables and detectors; each for selected frequency ranges making the measurements time consuming and difficult. [403,404] With the development of high frequency microelectronic and the research on the stealth of rockets and aircrafts [405,406] in the 1990s, new instruments called Network Analyzers, working up to tens of GHz range made the measurements easier and faster. Nowadays, the link with far-infrared absorption is at the same time possible (also called THz spectroscopy).…”