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Title: Effect of crystal structure and cationic order on phonon modes across ferroelectric phase transformation in Pb(Fe{sub 0.5-x}Sc{sub x}Nb{sub 0.5})O{sub 3} bulk ceramics

Pb(Fe{sub 0.5-x}Sc{sub x}Nb{sub 0.5})O{sub 3} [(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(Sc{sub 0.5}Nb{sub 0.5})O{sub 3} (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 [F{sub 1u}, ∼250 cm{sup −1}] and BO{sub 6} octahedral rotational mode [F{sub 1g}, ∼200 cm{sup −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 localizedmore » 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 BO{sub 6} rotational modes introduces a weak relaxor feature for systems with rhombohedral symmetry in PFSN ceramics, which was confirmed from the macroscopic dielectric studies.« less
Authors:
;  [1] ;  [2]
  1. Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Kandi, Sangareddy - 502285, Telangana (India)
  2. School of Engineering, Indian Institute of Technology Mandi, 175001, Himachal Pradesh (India)
Publication Date:
OSTI Identifier:
22492402
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 6; Journal Issue: 1; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; BOND ANGLE; CATIONS; CERAMICS; CORRELATIONS; ELECTRON DIFFRACTION; FERROELECTRIC MATERIALS; HARDENING; IRON COMPOUNDS; LEAD COMPOUNDS; MONOCLINIC LATTICES; NIOBATES; PHASE TRANSFORMATIONS; PHONONS; RAMAN EFFECT; RAMAN SPECTRA; REFLECTION; SCANDIUM COMPOUNDS; SUPERLATTICES; TEMPERATURE DEPENDENCE; TRIGONAL LATTICES