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Type: Artigo de periódico
Title: Synchrotron X-ray diffraction and Raman spectroscopy of Ln(3)NbO(7) (Ln=La, Pr, Nd, Sm-Lu) ceramics obtained by molten-salt synthesis
Author: Siqueira, KPF
Soares, JC
Granado, E
Bittar, EM
de Paula, AM
Moreira, RL
Dias, A
Abstract: Ln(3)NbO(7) (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) ceramics were obtained by molten-salt synthesis and their structures were systematically investigated by synchrotron X-ray diffraction (SXRD), second harmonic generation (SHG) and Raman spectroscopy. It was observed that ceramics with the largest ionic radii (La, Pr, Nd) crystallized into the Pmcn space group, while the ceramics with intermediate ionic radii (Sm-Gd) exhibited a different crystal structure belonging to the Ccmm space group. For this last group of ceramics, this result was corroborated by SHG and Raman scattering and ruled out any possibility for the non-centrosymmetric C222(1) space group, solving a recent controversy in the literature. Finally, according to SXRD, Tb-Lu containing samples exhibited an average defect fluorite structure (Fm (3) over barm space group). Nonetheless, broad scattering at forbidden Bragg reflections indicates the presence of short-range domains with lower symmetry. Vibrational spectroscopy showed the presence of six Raman-active modes, inconsistent with the average cubic fluorite structure, and in line with the existence of lower-symmetry nano-domains immersed in the average fluorite structure of these ceramics. (C) 2013 Elsevier Inc. All rights reserved.
Subject: Synchrotron X-ray diffraction
Raman spectroscopy
Country: EUA
Editor: Academic Press Inc Elsevier Science
Rights: fechado
Identifier DOI: 10.1016/j.jssc.2013.10.015
Date Issue: 2014
Appears in Collections:Unicamp - Artigos e Outros Documentos

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