Near-Stoichiometric Barium Titanate Synthesis by Low Temperature Hydrothermal Reaction
- PDF / 2,003,886 Bytes
- 6 Pages / 414 x 635.4 pts Page_size
- 3 Downloads / 239 Views
193 Mat. Res. Soc. Symp. Proc. Vol. 606 0 2000 Materials Research Society
EXPERIMENT Hydrolysis of Ti-Precursor Each Ti-precursor was added to large excess of water with vigorous stirring. This solution was stirred for 30 more minutes before the separation of the solid residue by centrifugation. To investigate the hydrolysis behavior of Ti(OCH2 CH 2OCH 3)4 precursor in NaOH solution, the solid residue was separated from the mixed solution just before hydrothermal treatment in the synthetic process of BaTiO 3. The solid residues were dried at 60 'C in a vacuum oven overnight and sampled as disk specimen mixed with KBr to obtain FT-IR spectra (Nicolet Magna 750). Synthesis and Characterization of BaTiO, Ti(OCH 2CH 2OCH 3)4 in 4eq. 2-propanol was added to IM Ba(OAc) 2 aqueous solution with vigorous stirring. The combined solution was stirred for 30 more minutes for homogeneous mixing. Meanwhile, NaOH solution (pH>13.5 in the final mixture [4]) was prepared in a PTFE lined stainless steel autoclave with stirring and heating equipment. The mixed solution was poured into the autoclave and underwent hydrothermal reaction under the condition of 80 'C, 1 hr period, 0.20 M [5]. The reaction variables were the pressure (autogeneous - 10 atm) and the Ba/Ti mole ratio (1.0 - 2.5) of the reactants. After the hydrothermal reaction was done, the reacted solution was cooled down in a cold water bath and washed with ammonia water three times using centrifugation. Then the solid product was dried at 80 °C in a vacuum oven for 12 hours. Some particles were calcined for 1 hr at various temperatures (400 - 1200 °C) under moisture free air using a box furnace. Surface morphology of BaTiO 3 particles was measured by FE-SEM (Hitachi S-4200). Each specimen was sensitized with Au-sputtering to avoid charging during SEM analysis. The crystalline structure of BaTiO 3 particles was determined by XRD (Shimadzu XRD-6000 or Rigaku Miniflex) analysis using Cu K, radiation. Raman spectra were obtained using PerkinElmer System 2000. Elemental analysis of BaTiO 3 powders was performed by ICP spectroscopy (Thermo Jariellash, Polyscom 61E). RESULTS AND DISCUSSION Hydrolysis Behavior and Particle Morphology FT-IR spectra are shown in Figure 1 to compare the hydrolysis behaviors of Ti-precursors. Peaks at 1,020 ~ 1,125 cm-1 correspond to Ti-O-C stretching vibrations. Intensity decrease and/or disappearance of these peaks is related to the partial and/or complete hydrolysis of titanium precursors. Because of methoxy substituent, methoxyethoxide can have electronic, steric, and weakly chelating effects around titanium ion so that it makes stronger bond with titanium ion than simple alkoxide. This has appeared as the partial hydrolysis of Ti(OCH 2CH 2OCH 3)4 in (b) as a comparison with the case of Ti(OCH(CH 3)2)4 in (a), which underwent complete hydrolysis under the same condition. Methoxyethoxide groups were still partially retained even in asprecipitated powder (c), which was collected from KOH solution. These results suggest that the partial and slow hy
Data Loading...
