Influence of Volatile Chlorides on the Molten Salt Synthesis of Ternary Oxide Nanorods and Nanoparticles

Abstract

A molten salt synthesis route, previously reported to yield BaTiO3, PbTiO3, and Na2Ti6O13 nanorods, has been re-examined to elucidate the role of volatile chlorides. A precursor mixture containing barium (or lead) and titanium was annealed in the presence of NaCl at 760 or 820 degrees C. The main products were respectively isometric nanocrystalline BaTiO3 and PbTiO3. Nanorods were also detected, but electron diffraction revealed that the composition of the nanorods was respectively BaTi2O5/BaTi5O11 and Na2Ti6O13 for the two different systems, in contradiction to the previous studies. It was shown that NaCl reacted with BaO (PbO) resulting in loss of volatile BaCl2 (PbCl2) and formation and preferential growth of titanium oxide-rich nanorods instead of the target phase BaTiO3 (or PbTiO3). The molten salt synthesis route may therefore not necessarily yield nanorods of the target ternary oxide as reported previously. In addition, the importance of NaCl(g) for the growth of nanorods below the melting point of NaCl was demonstrated in a special experimental setup, where NaCl and the precursors were physically separated.

Molten Salt Synthesis of Ceramic Powders

“…For example, needlelike PbTiO 3 particles are formed by heating of a mixture of equiaxed PbTiO 3 particles, NaCl, and surfactant (Cai, et al, 2007) and non-equiaxed BaTiO 3 particles are prepared from equiaxed nano TiO 2 particles without a surfactant . Careful examination of product particles is necessary because the formation of titanium oxide-rich compounds, instead of PbTiO 3 and BaTiO 3 , is possible (Rørvik et al, 2008).…”

Ferroelectric nanoparticles, wires and tubes: synthesis, characterisation and applications

“…Another solution-based 55 approach for producing 1D ferroelectric material is molten-salt synthesis, which has used for the large scale production of nanoferroelectrics. [73][74][75][76] This method involves the reaction of precursors in a molten salt medium, such as NaCl or KCl melt, which leads to the precipitation of the nanostructures. Molten-60 salt synthesis can be carried out over short time duration (1 to 4 hours) using common salts of constituent materials, making this approach more facile and environmentally benign compared to hydro/solvothermal methods.…”

“…Molten-60 salt synthesis can be carried out over short time duration (1 to 4 hours) using common salts of constituent materials, making this approach more facile and environmentally benign compared to hydro/solvothermal methods. [73][74][75][76] The basic formation mechanism of nanostructures by molten-salt methods is 65 dependent on the control of surface and interface energies of precursors and salt used; different morphologies can be formed by varying the salt or precursor concentrations. [73][74][75][76] 1D nanostructures of common ferroelectrics such as BaTiO3 ( Figure 3(d)) 73 , SrTiO3, and PbTiO3 have been synthesised by this 70 method.…”

“…[73][74][75][76] The basic formation mechanism of nanostructures by molten-salt methods is 65 dependent on the control of surface and interface energies of precursors and salt used; different morphologies can be formed by varying the salt or precursor concentrations. [73][74][75][76] 1D nanostructures of common ferroelectrics such as BaTiO3 ( Figure 3(d)) 73 , SrTiO3, and PbTiO3 have been synthesised by this 70 method. [73][74][75][76] Electrospinning has also been used to produce high aspect ratio 1D nanofibers and wires of ferroelectric materials, 52,[105][106][107]118 e.g.…”

“…[73][74][75][76] 1D nanostructures of common ferroelectrics such as BaTiO3 ( Figure 3(d)) 73 , SrTiO3, and PbTiO3 have been synthesised by this 70 method. [73][74][75][76] Electrospinning has also been used to produce high aspect ratio 1D nanofibers and wires of ferroelectric materials, 52,[105][106][107]118 e.g. BaTiO3 nanofibers 52 .…”