Growth mechanism and electrical properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals by a modified Bridgman method

Relaxor-based piezoelectric Pb[(Zn1/3Nb2/3)(0.91)Ti-0.09]O-3 (PZNT 91/9) single crystals 28 mm in diameter and 30 mm in length were grown by a modified Bridgman technique with PbO flux using an allomeric seed crystal. The crystals were grown in sealed platinum crucibles at about 1250degreesC. The obtained crystals are of pure perovskite structure within the sensitivity of X-ray diffraction measurement and the as-grown crystals have three appearing faces with slight deviation in angle from the pseudocubic (001)(cub) face. The growth mechanism of the PZNT crystals could be explained from the viewpoint of the formation of growth units and the incorporation of growth units into different interfaces of the crystal lattice. The growth rate of various crystal faces is related to the assembling modes of the growth units into different interfaces. Assembling of [BO6] octahedral growth unit into (111)(cub) interface has the strongest bonding force, and this crystal direction has the fastest growth rate; therefore, (111)(cub) crystal face disappears, assembling of [BO6] into (001)(cub) interface has the smallest bonding force, and this crystal face has the smallest growth rate; therefore, (001)(cub) crystal face appears. The growth steps aligning approximately along the <001>(cub) direction reveal that (001)(cub) face proceeds by a layer growth mechanism controlled by two-dimensional nucleation starting at crystal corners or edges. Dielectric measurement proves that the quality of the obtained PZNT crystals is good. Domain observation shows that both the rhombohedral and tetragonal orientation state domain coexist in the morphotropic PZNT 91/9 single crystals. (C) 2002 Elsevier Science B.V. All rights reserved.