Scandium induced structural transformation and B′:B″ cationic ordering in Pb(Fe0.5Nb0.5)O3 multiferroic ceramics

摘要

The current study explores non-magnetic Sc3+ induced structural transformation, evolution of local B-site cation ordering and associated effect on ferroelectric phase transition temperature Tmax (temperature corresponding to dielectric maxima) on increasing the atom percent of Sc substitution in [Pb(Fe0.5Nb0.5)O3 (PFN)] ceramics. In this regard, the phase pure Pb[(Fe0.5−xScx)Nb0.5]O3 ceramics with x varying from 0 to 0.5 were synthesized through solid state reaction route. The detailed structural analysis through Rietveld refinement confirms the room temperature transformation from a monoclinic Cm to rhombohedral R3m structure at x = 0.3 mol. % of Sc. Absorption spectra studies show that there is a considerable increment in the bandgap at higher scandium content. Most interestingly, the Tmax exhibited an increment for lower scandium contents (x = 0.1 to 0.25) followed by a drop in Tmax (x = 0.3 to 0.5). Such anomalous behavior in Tmax is expected to arise due to the onset of B′, B″ local cation ordering beyond Sc content x = 0.25. The B-site cation ordering at and beyond x = 0.3 was also confirmed by the evolution of cation order induced Pb-O coupled vibrational mode in Raman scattering studies. In addition, the Mössbauer spectra of PFN (x = 0) and Pb(Fe0.4Sc0.1Nb0.5)O3 (x = 0.1) are reported to verify the spin state and oxidation state of iron. The lattice distortion due to the radius ratio difference between a Sc3+ cation and Fe3+ cation in low spin state is responsible for the structural transformation, which in turn facilitates a B′:B″ cation ordering.