Microwave Assisted Semi-Solvothermal Synthesis of Nanocrystalline Barium Titanate

In an endeavor to synthesize tetragonal nanocrystallites of BaTiO₃ at much reduced reaction time, we explored the possibility of performing microwave assisted semi-solvothermal reaction by using Ba(OH)₂·8H₂O and amorphous titanium hydrous gel as precursors and 1,4-butanediol and water as solvent. Typically, such a microwave assisted reaction was accomplished within 2 hrs at 220 °C as against 12 hrs required in conventional approach. The crystallized BaTiO₃ powders (microwave assisted as well as conventionally processed for reference) were characterized by X-ray diffraction, thermal analysis, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. We have detected metastable cubic phase by XRD while locally symmetric tetragonal phase by Raman spectroscopy in case of conventional semi-solvothermal processing. On the contrary, we could detect co-existence of tetragonal and cubic phases by XRD and only tetragonal phase by Raman spectroscopy in case of microwave assisted semi-solvothermal processing. The TEM analysis indicates typical particle size distribution in the range of ∼20 to 80 nm for conventionally processed powder while that in the range of ∼20 to 50 nm for microwave processed powder. HRTEM images evince the distortion from an ideal cubic structure in case of microwave processed powder which can be correlated with anisotropic lattice contraction during the microwave induced heating. AFM analysis exhibited relatively less aggregation of nanoparticles for microwave assisted process.