Ferroelectric properties and core shell domain structures of Fe-modified 0.77Bi0.5Na0.5TiO3-0.23SrTiO3 ceramics

The crystal structure, domain patterns, and ferroelectric properties of Fe-modified BNT-ST [0.77(Bi0.5Na0.5)TiO3-0.23Sr(Ti1-xFex)O3] ceramics, fabricated by a conventional solid-state reaction, were investigated. Core-shell structures were observed and the volume fractions of the core-domain and shell (relaxor-matrix) were found to be dependent on Fe-modification content. The crystal structures of the core-domain and the relaxor-matrix were rhombohedral with the space group R3c, and the tetragonal with the space group P4bm, respectively. Compositional inhomogeneity, specifically, the enrichment of Bi3+ and Na+ and the considerable depletion of Sr2+, were observed in the core-domain region, and was reduced by substituting Ti4+ with Fe3+. The Fe-modification of the BNT-23ST ceramics promoted the diffusion of Sr2+ ions into the core region and shifted ferroelectric behaviour towards ergodic-relaxor behaviour. This improved the effective d33* of BNT-23ST ceramics to over 500 pm/V at 2 kV/mm.