Growth and some electrical properties of lead-free piezoelectric crystals (Na1/2Bi1/2)TiO3 and (Na1/2Bi1/2)TiO3-BaTiO3 prepared by a Bridgman method

The (Na1/2Bi1/2)TiO3 (NBT)-based crystals with pure perovskite structure and a size of φ20×80 mm have been grown by a Bridgman method directly from their melt. This method is more suitable for the growth of large crystals than previous methods. To grow perfect crystals, it is necessary to overcome such issues as Pt crucible leaking, composition volatilizing and crystal cracking. The NBT-based crystals were characterized by the cubic growth habit and grew mainly along [1 1 1] in the Bridgman growth. XRD data indicate that NBT crystals are rhombohedral and 0.94NBT-0.06BT ones are rhomboheral in the most part. The broad dielectric peaks and frequency dispersion demonstrate their relaxor ferroelectric behaviors. The piezoelectricity of NBT starts to disappear from T=200 °C. Meanwhile, there are two dielectric anomalies at Trt∼198 °C and Tm∼330 °C in 0.94NBT-0.06BT crystals and their piezoelectric constant d33 reduce to zero after annealing at 220°C (near Trt) for 30 min.