Influence of BaTiO3 Content on the Structure and Properties of Na0.5Bi0.5TiO3 Crystals

Lead-free Na0.5Bi0.5TiO3-x%BaTiO3 single crystals of different compositions (x=0, 2, 4, 4.5 and 5.5) were grown using a top-seeded solution growth method. Temperature-dependent X-ray diffraction revealed the presence of a high-temperature tetragonal phase that existed over a narrow composition range of 0<x<2, at temperatures far in excess of the ferroelectric Curie temperature T-c. Polarized light microscopy images confirmed the presence of tetragonal domains in NBT that persisted until T-c+250 degrees C; whereas for x>4, rhombohedral domains were found that persisted on heating to only about T-c-150 degrees C. Investigations of the properties revealed a dramatic increase in the dielectric constant (upto 500%), a decrease in the coercive field (300%), and an increase in the longitudinal piezoelectric constant (1000%) with modest increases in x, as the high-temperature tetragonal ferroelastic phase was suppressed and as the morphotropic-phase boundary approached.