Electric-field-induced local structural phenomena in relaxor ferroelectric PbSc(0.5)Nb(0.5)O3 near the intermediate temperature T* studied by Raman spectroscopy.
Raman spectroscopy at different temperatures and under an external electric field E was applied to PbSc0.5Nb0.5O3 single crystals in order to gain further insights into the mesoscopic-scale coupling processes in perovskite-type (ABO3) relaxor ferroelectrics. Parallel and cross-polarized Raman spectra were collected between 800-80 K with E applied along the cubic [1 0 0], [1 1 0] or [1 1 1] crystallographic directions. The analysis was focused on the field-induced changes in the temperature evolution of three low-energy phonon modes: the Pb-localized mode near 50 cm(-1), the Pb-BO3 translation mode near 150 cm(-1), and the B-cation-localized mode near 250 cm(-1). The results show that competitive ferroelectric (FE) and antiferroelectric (AFE) coupling exists within the system of off-centred Pb(2+) cations, within the system of off-centred B-site cations as well as between off-centred Pb(2+) and B-site cations. The strong AFE-type coupling between Pb(2+) cations along the cubic body diagonal significantly influences the coupling between the B-site cations via the Pb-BO3 mode and results in AFE-type behaviour of the 'microscopic' T* determined from the B-cation-localized mode near 250 cm(-1), which explains the previously reported non-trivial field dependence of the 'macroscopic' characteristic temperatures: the temperature of the dielectric-permittivity maximum Tm, T*, and the Burns temperature TB. The comparative analysis between PbSc0.5Nb0.5O3 and PbSc0.5Ta0.5O3 indicates that two major displacive order parameters couple to form a relaxor state in B-site complex perovskites: the FE order associated with polar shifts of B-site cations and the AFE order associated with polar shifts of A-site cations. The latter penetrates through both polar and non-polar regions, but it is highly frustrated due to the high density of translation-symmetry faults in the chemical NaCl-type B-site order. The frustrated AFE order of off-centred A-site cations might be the key factor for the existence of a relaxor state.
Fachbereich Geowissenschaften, Universität Hamburg, Grindelallee 48, D-20146 Hamburg, Germany.
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T
Steilmann
B J
BJ
Maier
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M
Gospodinov
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U
Bismayer
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B
Mihailova
D017610:Calcium Compounds / Q000737:chemistry* / Q000528:radiation effects*; D017097:Electric Impedance; D004574:Electromagnetic Fields; D008422:Materials Testing; D008956:Models, Chemical; D008958:Models, Molecular; D010087:Oxides / Q000737:chemistry* / Q000528:radiation effects*; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013696:Temperature; D014025:Titanium / Q000737:chemistry* / Q000528:radiation effects*
D017610:Calcium Compounds; D010087:Oxides; C059910:perovskite; D014025:Titanium