Thermal and compositional driven relaxor ferroelectric behaviours of lead-free Bi0.5Na0.5TiO3-SrTiO3 ceramics

The dielectric, piezoelectric and ferroelectric properties of (1 - x)(Bi0.5Na0.5)TiO3-xSrTiO(3) (BNT-ST) ceramics (0 <= x <= 0.30) are systematically studied in order to investigate their relaxor ferroelectric behaviours driven by thermal and compositional changes. The significant enhancement of the piezoelectric coefficient (d(33) = 152 pC N-1) has been observed for x = 0.20. In addition, the BNT-24ST ceramic exhibits an electric field-induced strain of 0.20% at 7 kV mm(-1) and a normalized strain d(33)* of 266 pm V-1. The increase in the ST content drives BNT from the ferroelectric to relaxor ferroelectric state due to the rising disordering level. In addition, the behaviours of the field-induced metastable ferroelectric to relaxor phase transition are studied based on the anomalies in the temperature dependence of the dielectric properties. To investigate the thermal-induced domain behaviour, in situ piezoresponse force microscopy (PFM) is used to observe the domain structures of the poled BNT-16ST ceramic upon heating and cooling. This study provides evidence for understanding the relaxor ferroelectric behaviours of the BNT-ST ceramics.