Formation of Lead Niobates in Molten Salt Systems

Abstract

The formation mechanisms, phase stability, impurity incorporation, and morphological characteristics of lead niobates obtained by molten salt synthesis were studied by X‐ray diffraction analysis, scanning electron microscopy, and energy dispersive analysis. Results indicate that PbO is the fastdissolving component of the constituent oxides and that the formation of lead niobates initiates at the surface of Nb 2 O 5 powders. Reaction rates were faster in molten salts when compared to those of solid‐state synthesis. Significant morphological differences were observed between the powders prepared by both solid‐state and molten salt synthesis. At low PbO/Nb 2 O 5 molar ratios, reaction between starting powders and molten salts resulted in the formation of NaNbO 3 , along with potassium incorporation into lead niobates. Orthorhombic PbNb 2 O 6 , monoclinic Pb 2 Nb 2 O 7 , and fcc Pb 3 Nb 3 O 8 phases were stabilized using molten salt synthesis, while only rhombohedral PbNb 2 O 6 and Pb 2 Nb 2 O 7 , and tetragonal Pb 3 Nb 2 O 8 , were obtained by solid‐state synthesis. Molten salt compositions containing PbO/Nb 2 O 5 ratios of 2 and 3 resulted in the stabilization of phases different from those obtained using solid‐state synthesis. For a PbO/Nb 2 O 5 ratio equal to 3, Pb 5 Nb 4 O 13 observed in solidstate synthesis was not found in the products of molten salt synthesis.