Sol-Gel Processing and Structure Development of Lead Titanate Particles
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797 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
Organic pyrolysis and crystallization of PT particles were studied using DTA, TGA and XRD. TGA was used to determine organic pyrolysis behavior and distinguish DTA crystallization exotherms from organic pyrolysis exotherms. DTA and TGA scanning rates were 10 'C/min with air purging. XRD was carried out on particles which were heated in a box furnace in air for 0.5 hours, followed by an air quench. The oligomeric structure of modified PT alkoxide solutions was investigated using FTIR spectroscopy in transmission through KBr disks; FTIR spectra for the PT stock solution, 2-MOE, and BA (2M) in 2-MOE were also collected for comparison. PT particle structure was studied using diffuse reflectance FTIR (DRIFT) spectroscopy. Particles were solvent cast from IPA onto a gold coated microscope slide. Heat treatments were carried out at 10 °C/min from 50 to 450 °C, with spectra collected at intermediate temperatures. Data was also collected for particles heated isothermally for 1 hour at 450 0 C. Care was taken to analyze the same region of the sample after each heat treatment. DRIFT spectra are compared to TGA data. SEM was carried out to determine the effect of solution aging time (before precipitation) on particle morphology. Additionally, particle and solution compositions were determined using ICP mass spectroscopy. RESULTS AND DISCUSSION Figure 1 shows FTIR spectra for the PT stock solution, modified PT solution, 2-MOE, and 2M BA in 2-MOE. The two peaks near 1600 cm-I can be assigned to the CO0- group of the benzoate ligand; the difference between vsym (COO-) and Vasym (COO-) (Av=40 cm- 1 ) in the modified PT solution spectra indicates bidentate chelation. Assignment was made by comparison with similar structures formed from chelation of Ti alkoxides with acetic acid [6]. The FTIR spectra confirm that the benzoic acid reacts with the PT alkoxide. More reactive methoxyethoxide groups are replaced with bulkier, less reactive benzoate ligands. However, the extent of replacement cannot be determined from the FTIR data.
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Wavenumber (cm-) Figure 1. FTIR spectra for 1) PT stock solution, 2) modified PT stock solution, 3) 2-MOE, and 4) 2M BA in 2-MOE.
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When modified and aged PT solutions are added to IPA, a precipitate immediately forms. This initial precipitate redissolves upon stirring; permanent particle formation then occurs within 30 minutes. An increase in Rh and Rm causes particles to precipitate faster (i.e., in less than 30 minutes). When a similar concentration of unmodified PT stock solution is added to IPA, no precipitation is observed. ICP mass spectroscopy data show that the modified alkoxide solution and particles have the same stoichiometry, approximately that of PbTiO 3 . No phase separation occurred during modification or particle formation. This result is supported by the development of a single crystalline phase, as demonstrated by the XRD data below. DTA data for PT pa
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