Low temperature dielectric relaxation phenomena in relaxor ferroelectric strontium barium niobate single crystals

Abstract

Low temperature (15∼300K) dielectric permittivities of tungsten bronze Sr_1–xBa_xNb₂O₆ (SBN(1–x)%, 1–x=0.50, 0.61, and 0.75) single crystals were studied using dielectric spectrum techniques. Two distinct dielectric relaxation features were observed in all three crystal compositions. The dielectric anomaly at temperature range ∼(150K–300K) is presumably associated with the incommensurate (ICS) superlattice transformation identified by high resolution TEM (Bursill and Lin)¹ No experimental evidence of phase transition was found in the measurement regime for the dielectric anomaly observed at temperature below 150K. Dielectric properties of the poled crystals indicate that the ICS related dielectric anomaly is strongly dependent on the polarization-strain coupling along the c-direction, while the second low temperature relaxation is associated to the polarization fluctuation in the a-b plane related to the relaxor nature of the SBN solid solution system. The experimental results further substantiate the thermally agitated polarization perturbation model. It is suggested that the dielectric relaxation phenomenon of ferroelectric tungsten bronzes SBN at low temperatures underlines the deformed oxygen octahedral structure with the added characteristics of the freezing-in of the relaxor polarization fluctuations.