Facile Low Temperature Hydrothermal Synthesis of BaTiO₃ Nanoparticles Studied by <em>In Situ</em> X-ray Diffraction

Abstract

Ferroelectric materials are crucial for today&amp;rsquo;s technological society, and nanostructured ferroelectric materials are important for downscaling of devices. Controlled and reproducible synthesis of these materials are therefore of immense importance. Hydrothermal synthesis is a well-established synthesis route, with a large parameter space for optimization, but a better understanding of nucleation and growth mechanisms is needed for full utilization and control. Here we use in situ X-ray diffraction to follow the nucleation and growth of BaTiO3 formed by hydrothermal synthesis using two different titanium precursors, an amorphous titania precipitate slurry and a Ti-citric acid complex solution. Sequential Rietveld refinement was used to extract the time dependency of lattice parameters, crystallite size, strain and atomic displacement parameters. Phase pure BaTiO3 nanoparticles 10 - 15 nm in size were successfully synthesized at different temperatures (100, 125, and 150 &amp;deg;C) from both precursors after reaction times ranging from a few seconds, to several hours. The two precursors resulted in phase pure BaTiO3 with similar final crystallite size. Finally, two different growth mechanisms were revealed, where the effect of surfactants present during hydrothermal synthesis is discussed as one of the key parameters.

Reaction Pathway of the Hydrothermal Synthesis of AgCuO2 from In Situ Time-Resolved X-ray Diffraction

“…The B iso values obtained are rather large, which is similar to what we have observed in previous in situ studies. 33 Again, the presence of hydroxyl groups could be the reason for the higher B iso values obtained in these type of studies. 34 For AgCuO 2 crystals formed at all the reaction temperatures, the Ag atom B iso values are generally larger than those for Cu atoms, indicating a higher thermal motion for Ag ions in the AgCuO 2 crystals.…”

“…As in previous studies, the values are nevertheless higher than what would be expected for a solid sample, but the presence of hydroxyl ions or water molecules within the structure has been proposed to account for it. 25,33,34 Lastly, the strain was also monitored for the different temperatures (Figure 4f). For crystals formed at higher temperatures, the strains were generally lower than those formed at lower temperatures, again as expected since higher temperatures are favoring a better crystallization and strain relaxation.…”