Molten salt synthesis (MSS) is one of the important methods of preparing ceramic powders. Molten salts are used as a reaction aid to prepare complex oxides from their constituent oxides. Particulate materials with shape anisotropy are prepared by this technique and used as starting materials for grain-oriented ceramics.

The purpose of the work is to investigate the formation of Bi₄Ti₃O₁₂ using the molten salt method. The conventional method requires a high calcination temperature, usually leading to particle coarsening and aggregation of the Bi₄Ti₃O₁₂ powders. Ferroelectric Bi₄Ti₃O₁₂ is a suitable material for applications at high temperature transducers, capacitors and sensors.

In the present study, the influence of parameters of synthesis (temperature, time) and salt contents on morphology and size of Bi₄Ti₃O₁₂  crystals were investigated. Two kinds of eutectic salt mixtures, 0.5 NaCl + 0.5 KCl or 0.742 Na₂SO₄ + 0.258 K₂SO₄ were used as the flux. Eutectic temperatures are 650ºC and 831ºC for the chloride and sulfate fluxes, respectively. Mechanically mixed Bi₂O₃ – TiO₂ mixture was used as the starting material.

The mixtures of the precursors and salts were placed in a sealed alumina crucibles and heated at temperatures ranging from 700 to 1100ºC for a desired time period. The product obtained was washed with hot water several times until no trace of anion was detected by AgNO₃ or Ba(NO₃)₂ aqueous solution. The dried product was examined by XRD analysis. The particle morphology was examined by scanning electron microscopy (SEM).

It has been found, that formation of Bi₄Ti₃O₁₂ was accelerated by the presence of molten salts. In both fluxes aggregated particles were obtained. Finally discrete plate-like particles were formed, on heating for longer periods or at higher temperatures. These results suggest that the molten salt method is useful not only for producing ultra-fine powders with anisotropy, but also for controlling the aggregation states of the powders.

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1. Anisotropic grain growth of bismuth titanate in molten salt fluxes
2. Use of X-ray powder diffraction method for study on synthesis and decomposition of K₂Ti₈O₁₇
3. Morphology control of K_0.5Bi_0.5TiO₃ and Na_0.5Bi_0.5TiO₃ ferroelectric ceramic powders by molten salt synthesis
4. Investigations on synthesis and microstructure of potassium titanates