Influence of precursor synthesis temperature and hydrothermal alkaline medium on agglomeration and crystal phase of barium titanate nanoparticles

Phase‑pure, cube‑like barium titanate (BaTiO3) nanoparticles were synthesized via hydrothermal treatment of a single‑source barium-titanium peroxo-hydroxide precursor. Precursor solutions prepared at room temperature, 0 °C, and –10 °C with various storage times exhibited Ba/Ti molar ratios ranging from 0.66 to 1.05 as determined by X-ray fluorescence. Cooling the precursor solution to –10 °C effectively suppressed the polymerization of Ti-O-Ti, yielding near‑ideal stoichiometry and finer precursor particles. Subsequent hydrothermal processing in NH4OH, KOH, and NaOH (0.5–10 M, 100–200 °C) revealed the strong dependence of agglomeration and morphology on the alkaline medium. While NH4OH and KOH resulted in severe agglomeration and the formation of micrometer‑scale conglomerates, hydrothermal treatment in 10 M NaOH at 200 °C produced well‑faceted, weakly agglomerated cubic BaTiO3 particles with edge lengths of approximately 200–500 nm. The particle-size distribution was further tuned by reducing the solution volume from 60 to 10 mL and increasing the total Ba + Ti concentration from 0.05 to 0.30 M, leading to sharper cubic morphologies and bimodal size distributions at higher concentrations. X-ray diffraction combined with Rietveld refinement confirmed phase‑pure BaTiO3 and demonstrated that the cooling rate governed the cubic‑to‑tetragonal phase transition through size‑ and strain‑mediated stabilization. Fourier-transform infrared spectroscopy, Fourier-transform Raman spectroscopy, and thermogravimetric-differential thermal analysis verified characteristic titanate bonding and BaCO3 contamination (~20 wt.%) at high feedstock concentration. The combination of low‑temperature precursor synthesis and NaOH‑mediated hydrothermal processing provides a scalable strategy for preparing morphology‑controlled BaTiO3 nanoparticles with potential relevance for electronic, electrooptic, and bioimaging applications.