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 N b z 0 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/Nbz05 molar ratios, reaction between starting powders and molten salts resulted in the formation of NaNb03, along with potassium incorporation into lead niobates. Orthorhombic PbNb206, monoclinic PbzNbz07, and fcc Pb3Nb308 phases were stabilized using molten salt synthesis, while only rhombohedra1 PbNbz06 and PbZNbz07, and tetragonal Pb3NbzOa, were obtained by solid-state synthesis. Molten salt compositions containing PbO/NbZO5 ratios of 2 and 3 resulted in the stabilization of phases different from those obtained using solid-state synthesis. For a PbO/Nbz05 ratio equal to 3, Pb5Nb4OI3 observed in solidstate synthesis was not found in the products of molten salt synthesis. [

Molten salt synthesis of lead lanthanum zirconate titanate ceramic powders

“…Differing shapes could be attributed to different particle growth mechanism in the molten salts at different soaking temperature, which might alter the activation energy for phase transformation and thus stabilize high-temperature polymorphs at low temperatures [10]. The activation energy for particle growth can be calculated from the plot of ln D 2 versus 1/T, which from the Arrhenius equation [20]:…”

“…In addition to low temperatures of formation, molten salts have stabilized different polymorphs when compared to other methods of synthesis [13]. Therefore, MSS has been widely used to form complex perovskite materials, like PZT [12,14], ferrites [15], PbNb 2 O 6 [10], PFN [16], PMN-PT [17,18], PLT [11]. However, the synthesis of single phase multicomponent compound PLZT was only reported by Namu at high temperature above 1100 • C by MSS using NaCl-KCl as the flux [19], which the chlorides were evaporated and led to pollute the environment.…”

“…The molten salt synthesis was one of the simplest techniques to prepare pure, stoichiometric ceramic powders of multicomponent oxides, in which the molten salt was used as a reaction aid or medium [8][9][10][11][12]. Because of the small diffusion distances of oxide mixtures in molten salts, high reactivity of salts, and high mobility of species, completed reactions can be achieved in a relatively short time [12].…”

Large-scale synthesis of Pb1−La TiO3 ceramic powders by molten salt method

“…Firstly, the starting oxides dissolve in the molten salts, followed by the formation of the product in solution with the molten salt, and finally precipitation of the product beyond its solubility limit [20]. During the molten salt synthesis process, the crystal morphology was developed in a two-stage process: the nucleation process and the growth process.…”

Synthesis of LiMn1/3Ni1/3Co1/3O2 in molten KCl for rechargeable lithium-ion batteries

“…reactants), which enables molecular level mixing of different reactants, and thus leads to a homogeneous structure of the final product [15]. It has been used extensively to prepare ferrites [16], titanates [17], niobates [18][19][20], and carbide [21]. The desired compound will form if it is thermodynamically more stable than the reactants.…”