Soft-mode spectroscopy in cubic (Ba0.8Sr0.2)Ti0.95(Zn1/3Nb2/3)0.05O3 by hyper-Raman scattering and the mechanism of the phase transition. (December 2016)

• Record Type: Journal Article
• Authors: Nabil, Dhifallah; Hehlen, Bernard; El Marssi, Mimoun; Mohamed, Dammak; Khemakhem, Hamadi
• Is Part Of: Solid state communications. Volume 248(2016)
• Page Start: 97
• Page End: 100
• Publication Date: 2016-12
• Subjects: B. Solid-state reaction -- C. Phase transition -- D. Raman spectroscopy -- D. Hyper-Raman scattering; Solid state chemistry -- Periodicals; Solid state physics -- Periodicals; Chimie de l'état solide -- Périodiques; Physique de l'état solide -- Périodiques; 530.41
• DOI: 10.1016/j.ssc.2016.09.016
• Languages: English
• ISSNs: 0038-1098

Abstract

Abstract: This paper presents a survey of soft modes and their relationship to structural phase transitions. After introducing the concept of a soft mode, the origin of softening is considered from a lattice-dynamical point. The Landau theory approach to structural transitions is then discussed, followed by a generalization of the soft-mode concept through the use of the dynamic order-parameter susceptibility. The hyper-Raman spectra in the cubic phase of (Ba0.8 Sr0.2 )Ti0.95 (Zn1/3 Nb2/3 )0.05 O3 are studied with special emphasis on the lowest-frequency phonon mode. The spectral structure is found to change above the Curie temperature (303–873 K). Soft modes were put forward by Cochran and Anderson about 50 years ago as an explanation of structural phase transitions. Extending Landau's theory of phase transitions, their prediction was that the square of the frequency of the soft mode was proportional to ω 0 ( T ) = C T − T C where Tc is the transition temperature. Highlights: Raman and Hyper-Raman spectra is in good agreement with the dielectric data. HRS is studied to clarify the controversies about the low frequency response. In approaching TC, we find a continuous decrease of the mode frequency ω0 .