Relaxor-like dynamics of ferroelectric K(Ta1− x Nb x )O3 crystals probed by inelastic light scattering

• Published in: Journal of applied physics 2014-08, Vol.116 (7)
• Main Authors: Rahaman, M. M., Imai, T., Miyazu, J., Kobayashi, J., Tsukada, S., Helal, M. A., Kojima, S.
• Format: Article
• Language: English
• Subjects: Applied physics; Broken symmetry; Crystals; Damping; Ferroelectric materials; Ferroelectricity; Inelastic scattering; Light scattering; Order disorder; Phase transitions; Raman spectra; Relaxors; Temperature dependence; Transition temperature; Variation
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4893363

The relaxor-like dynamics of the cubic-tetragonal ferroelectric phase transition was studied by Brillouin and Raman scattering in K(Ta1−xNbx)O3 (KTN) crystals with x = 0.40 (KTN40). The local symmetry breaking by the polar nanoregions (PNRs) was observed in a paraelectric phase by Raman scattering on the A1(z) mode of the PNRs with R3m symmetry. Upon cooling from a high temperature, the remarkable increase in the LA phonon damping starts at 45 K above the cubic-tetragonal phase transition temperature of TC-T = 308 K, which is defined as the intermediate temperature, T* ∼ 353 K, indicating the start of the rapid growth of the PNRs. The coupling between the LA mode and fluctuation of the PNRs caused a remarkable elastic anomaly in the vicinity of TC-T. The analysis of the temperature dependent central peak shows a critical slowing down towards TC-T, which is the evidence for the order-disorder nature of a ferroelectric phase transition. The evolution of the dynamic PNRs is discussed by the estimation of their length scale, and it is found that it starts to increase near T* and gradually grows towards TC-T.