Effect of crystal structure and cationic order on phonon modes across ferroelectric phase transformation in Pb(Fe0.5-xScxNb0.5)O3 bulk ceramics

B, Mallesham and B, Viswanath and Ramadurai, Ranjit (2016) Effect of crystal structure and cationic order on phonon modes across ferroelectric phase transformation in Pb(Fe0.5-xScxNb0.5)O3 bulk ceramics. AIP Advances, 6 (1). pp. 1-8. ISSN 2158-3226

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Pb(Fe0.5-xScxNb0.5)O3 [(PFSN) (0 ≤ x ≤ 0.5)] multiferroic relaxors were synthesized and the temperature dependence of phonon modes across ferroelectric to paraelectric transition was studied. With varying Sc content from x = 0 to 0.25 the structure remains monoclinic and with further addition (x = 0.3 - 0.5) the structure transforms into rhombohedral symmetry. Structural refinement studies showed that the change in crystal structure from monoclinic to rhombohedral symmetry involves a volume increment of 34-36%. Associated changes in the tolerance factor (1.024 ≤ t ≤ 0.976) and bond angles were observed. Structure assisted B′-B″ cation ordering was confirmed through the superlattice reflections in selected area electron diffraction (SAED) pattern of Pb(Sc0.5Nb0.5)O3 (x = 0.5). Cation ordering is also evident from the evolution of Pb-O phonon mode in Raman spectra of compositions with rhombohedral symmetry (x ≥ 0.3). The high temperature Raman scattering studies show that the B-localized mode [F1u, ∼250 cm−1] and BO6 octahedral rotational mode [F1g, ∼200 cm−1], both originating from polar nano regions (PNRs) behave like coupled phonon modes in rhombohedral symmetry. However, in monoclinic symmetry they behave independently across the transition. Softening of B localized mode across the transition followed by the hardening for all compositions confirms the diffusive nature of the ferroelectric transformation. The presence of correlation between the B localized and BO6 rotational modes introduces a weak relaxor feature for systems with rhombohedral symmetry in PFSN ceramics, which was confirmed from the macroscopic dielectric studies.

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IITH Creators:
IITH CreatorsORCiD
Ramadurai, Ranjithttp://orcid.org/0000-0003-2991-0027
Item Type: Article
Subjects: Others > Metallurgy
Others > Nanotechnology
Physics > Astronomy Astrophysics
Materials Engineering > Materials engineering
Divisions: Department of Material Science Engineering
Depositing User: Library Staff
Date Deposited: 03 Feb 2016 06:27
Last Modified: 20 Sep 2017 07:15
URI: http://raiith.iith.ac.in/id/eprint/2171
Publisher URL: https://doi.org/10.1063/1.4941341
OA policy: http://www.sherpa.ac.uk/romeo/issn/2158-3226/
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