Structural characterisation of ferroelectric Ag2Nb4O11 and dielectric Ag2Ta4O11

Nahum Masó; David I. Woodward; Pam A. Thomas; Alejandro Várez; Anthony R. West

doi:10.1039/C0JM02540B

Structural characterisation of ferroelectric Ag₂Nb₄O₁₁ and dielectric Ag₂Ta₄O₁₁†

Nahum Masó,*^a David I. Woodward,^b Pam A. Thomas,^b Alejandro Várez^c and Anthony R. West^a

* Corresponding authors

^a Department of Materials Science and Engineering, The University of Sheffield, Mappin Street, Sheffield, UK
E-mail: n.maso@sheffield.ac.uk

^b Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, UK

^c Dpto Ciencia e Ingeniería de Materiales e Ing. Química, Universidad Carlos III de Madrid, Avda. Universidad, 30, Leganes, Spain

Abstract

Structural characterisation of Ag₂Nb₄O₁₁ and Ag₂Ta₄O₁₁ powders has been carried out by Rietveld refinement of neutron powder diffraction data in the temperature range 10–573 K, symmetry-adapted mode analysis and second-harmonic generation. Ag₂Nb₄O₁₁ ceramics appear to be ferroelectric with a maximum permittivity of ∼150 at T_C ≈ 400 K, frequency-independent permittivity below this temperature and a shoulder in the ε′ vs. temperature profile at ∼200 K. The space group changes from R [3 with combining macron] c to R3c as the temperature decreases through T_C with a further transition from R3c to R3 below ∼200 K. The origin of the polar structure is related to displacement of Nb atoms in pentagonal bipyramids towards apical oxygens and in octahedra towards faces. This displacement towards octahedra faces is observed for some Ag atoms too. Ag₂Ta₄O₁₁ ceramics show temperature-independent permittivity of ∼20, with a centrosymmetric crystal structure, R [3 with combining macron] c. Comments on possible phase transition(s) of several compounds similar to Ag₂(Nb,Ta)₄O₁₁ are made.

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Article information

DOI: https://doi.org/10.1039/C0JM02540B
Article type: Paper
Submitted: 04 Aug 2010
Accepted: 01 Dec 2010
First published: 10 Jan 2011

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J. Mater. Chem., 2011,21, 2715-2722

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Structural characterisation of ferroelectric Ag₂Nb₄O₁₁ and dielectric Ag₂Ta₄O₁₁

N. Masó, D. I. Woodward, P. A. Thomas, A. Várez and A. R. West, J. Mater. Chem., 2011, 21, 2715 DOI: 10.1039/C0JM02540B

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