Formation of Alkoxy‐Derived lead Niobates in the PbO‐Rich Region

The formation of lead niobates in the PbO‐rich region is studied using powders prepared by the simultaneous hydrolysis of lead and niobium alkoxides. Cubic 3PbO·2Nb 2P O 5 solid solutions crystallize at low temperatures from amorphous materials having concentrations of 58 to 75 mol% PbO. The lattice parameter a increases linearly from 1.0544 to 1.0708 nm with increasing PbO. At higher temperatures the solid solutions made with 66.67 and 71.43 mol% PbO transform into 2PbO·Nb 2 O 5 (monoclinic) and 5PbO·2Nb 2 O s (monoclinic), respectively. Monoclinic 5PbO·2Nb 2 O 5 transforms into a new modification at = 3850° to = 3900°C. It has a rhombohedral unit cell with a = 0.7461 nm and c = 4.8092 nm ( a = 1.6599 nm, a = 25.97°). In the presence of excess lead, monoclinic 5PbO·2Nb 2 O 5 transforms into tetragonal 3PbO·Nb 2 O 5 .