tailieunhanh - Raman spectroscopy of CaCu3Ti4O12 ceramics revisited

This paper revises the imprints of Raman spectroscopy of this compound to validate its structural characteristics and optical behaviors. A special attention is paid on the account of optical phonons which show a recognizable agreement with the other results recently reported. | VNU Journal of Science: Mathematics – Physics, Vol. 34, No. 3 (2018) 79-84 Raman Spectroscopy of CaCu3Ti4O12 Ceramics Revisited Hoang Nam Nhat* Faculty of Engineering Physics and Nanotechnology, VNU University of Engineering and Technology, E4 Building, 144 Xuan Thuy, Cau Giay, Hanoi, Vietnam Received 18 September 2018 Accepted 24 September 2018 Abstract: The CaCu3Ti4O12 (CCTO) ceramic has been prepared by Solid State Reaction method in excess oxygen. It possesses a well-defined double-perovskite type crystalline structure and exhibits a colossal dielectric constant of around 50000 at room temperature. This paper revises the imprints of Raman spectroscopy of this compound to validate its structural characteristics and optical behaviors. A special attention is paid on the account of optical phonons which show a recognizable agreement with the other results recently reported. Keywords: CCTO, structure, optical phonon, ceramic method. 1. Introduction The double-perovskite type compound of the stochiometric content CaCu3Ti4O12 (abbreviated as CCTO) is known to possess a colossal dielectric constant at room temperature (~50000 for monocrystals and 30000 for polycrystallites [1, 2]) which can be tuned in a wide range by mean of doping of other element or by variation of preparation conditions. The larger is the wider is application range of the compound. Among the advantages of this compound belongs its high temperature stable dielectric constant from 100 to 600 K. Therefore, it is a valuable material for various device applications. The CCTO inherits its structure from perovskites and is usually crystalized in the Im3 space group (Th) with large unit cell containing 20 atoms. The Im3 space group has a mirror symmetry, therefore it prohibits a formation of spontaneous polarization. The inset in Fig. 1 shows two unit cells, where four perovskite units CaTiO3 are showed. As seen, the cations Cu2+ replace three cations Ca2+. The octaheders TiO6 are rotating with .

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