Investigation of local structure of lead‐free relaxor Ba(Ti_0.70Sn_0.30)O₃ by Raman spectroscopy

Abstract

The local structure of Ba(Ti0.70,Sn0.30)O3 (BSnT) was investigated using micro Raman spectroscopy from 80 to 500 K, which indicated three local phase sequences. The dielectric spectroscopy studies illustrated freezing of polar nano‐regions (PNR) below 95 K, merger of frequency dispersion at 220 K, and the origin of polar nano‐regions at 482 K. The temperature evolution of Raman spectra, basically integrated intensity, indicates non‐ergodic relaxor phase below 100 K, mature ergodic phase between 100 and 200 K, and the existence of ergodic polar clusters until 450 K, and above paraelectric phase. The observation of local phase sequences by Raman spectra are in agreement with dielectric spectroscopy anomalies. Copyright © 2008 John Wiley & Sons, Ltd.

Investigation of the depolarisation transition in Bi-based relaxor ferroelectrics

“…These data reveal a slight increase in intensity at 90 (10) C, close to the expected value of T d , that was found to be repeatable for both samples. A continuous reduction in intensity is observed across the range 150-400 C, indicating that PNRs are shrinking continuously, as observed in other lead-based 48 and leadfree 46,47 relaxor systems.…”

“…Between the temperatures 95-145 C, the intensity is maximised, indicating that T F is located within this range for both materials. 46,47 However, as the coherence length in Raman spectroscopy is expected to be only a few nm and therefore around 2 orders of magnitude less than that of SHG, it can be concluded that the phenomenon at T F is short-range and that on an atomic scale there is very little change in the material as it loses its macroscopic polarisation. At T B $ 400 C, the PNRs finally disappear.…”

“…At T B $ 400 C, the PNRs finally disappear. 46 SHG is shown to be extremely useful for (a) locating the relaxor-induced ferroelectric structural change arising from poling or field-cooling, (b) indicating the temperature range over which the poled regions shrink through the transition from field-induced ferroelectric to ergodic relaxor and (c) obtaining indicative values of T d and T F .…”

Lead‐Free Relaxor Ferroelectrics

“…For some BTZr compositions, the Burns temperature was estimated from thermal expansion measurements. 88 There is still some controversy regarding the nature of the low-temperature relaxor state in the isovalent-substituted BaTiO 3 compounds. Below T D~4 40 K, a deviation from linear behavior was observed indicating an electrostrictive strain due to formation of the local spontaneous polarization.…”

“…Bharadwaja et al assumed that re-entrant features in this system are due to a competitive dipole interaction between local ferroelectric and AFE order and/or local stresses. 58,88,90,105,106 Even though a perfect cubic symmetry forbids any Raman modes, the Raman spectrum in the paraelectric phase of pure BaTiO 3 has been reported at temperatures up to 570 K. It is considered as an indication of a strong local disorder due to random displacement of Ti 4+ ions at high temperatures. 102 They concluded that polar clusters develop from a ferroelectric state and re-enter the frozen disordered phase, instead of emerging from a paraelectric state as in most other relaxor ferroelectrics.…”