Effect of B-site Zr and Hf substitution on ferroelectric polar order for tetragonal tungsten bronze ceramic

Abstract

ABSTRACT Lead free ferroelectric ceramic Ba4Sm2Hf4Nb6O30(BSHN) with tungsten bronze structure was synthesized and characterized. The effect of B-site cation electron configuration (Hf and Zr) on origin of ferroelectricity and polarization reversal was also studied in detail. The X-ray diffraction (XRD) pattern was indexed with tetragonal tungsten bronze in P4bm space group for BSHN. Obvious dielectric anomaly was observed in the temperature dependent permittivity curve, and quite large thermal hysteresis was obtained from the differential scanning calorimetry (DSC) result. While at lower temperature (<T C), there are two distinct dielectric relaxations for BSHN, respectively related to the activation of frozen polar region and activation of the fully free reversal for the polarization. Compared with Ba4Sm2Zr4Nb6O30(BSZN), Hf substitution in B site makes it harder to activate the frozen polar nanoregion but easier to realize free polarization reversal. This could be further confirmed by the measured polarization-electric field (P-E) curve. Meanwhile, the Raman modes intensity showed gradual change rather than abrupt one for BSHN when the temperature increased through the Curie point, which was quite different from the Zr based compounds. The difference in BO6 octahedral tilting, B-site cation’s electron configuration and B-O bond character are the main cause of these distinct dielectric and ferroelectric property.