Hydrothermal synthesis of lead doped barium titanate

Lead doped barium titanate was synthesized hydrothermally at 363 K for 140 h. A molar formula of Ba_(1–x)Pb _x TiO₃ was used, where x ranged between 0.025 and 0.75. The crystal structure, phase purity, and particle morphology was investigated by x-ray diffraction, Raman spectroscopy and electron microscopy. Under the synthesis conditions used, lead (Pb²⁺) was shown to incorporate into the perovskite structure when the dopant was kept below 20%. Above 20% Pb, other phases appeared and at 75% Pb no reaction to the perovskite structure took place. Unexpectedly, barium titanate containing from 2.5% Pb to 10% Pb appeared to be of orthorhombic symmetry. This was concluded by total pattern fitting of x-ray diffraction profiles and from splitting of the 222 reflection. The factors controlling the tendency for these materials to adopt orthorhombic symmetry as opposed to the more commonly observed tetragonal or cubic symmetries are briefly discussed.