Soft-mode dynamics in micrograin and nanograin ceramics of strontium titanate observed by hyper-Raman scattering Auteur(s): Hehlen B., Al-Zein A., Bogicevic Christine, Gemeiner P., Kiat Jean-Michel (Article) Publié: -Physical Review B Condensed Matter And Materials Physics (1998-2015), vol. 87 p.014303 (2013) Ref HAL: hal-00787294_v1 DOI: 10.1103/PhysRevB.87.014303 WoS: 000313939200006 Exporter : BibTex | endNote 1 Citation Résumé: The low-frequency vibrations of micro- and nanograin ceramics of strontium titanate are investigated by hyper-Raman spectroscopy. The combination of a confocal optical microscope with an ultranarrow Notch filter enabled an accurate spectroscopy on both the Stokes and anti-Stokes side down to about 8 cm−1. A splitting of the soft mode into E-u- and A-2u-symmetry vibrations is clearly observed in the micrograin sample. The peculiar temperature dependence of ω^2_A2u−ω^2_Eu emphasizes a nonlinear coupling between the square of the TiO6 tilting angle and the spontaneous strain c/a − 1. In addition, the very different temperature behavior of the linewidth of the two soft components is assigned to the growth of a disorder anisotropy on cooling, probably on the titanium site. |