Crystallization of BaTiO[sub 3] from an X-ray amorphous, metal organic precursor was investigated by comparing samples heated in O[sub 2], air, argon, and CO[sub 2]. It is evident that an intermediate barium titanium oxycarbonate phase forms between 500 and 620C and that BaTiO[sub 3] forms directly by the endothermic decomposition of this phase between 635 and 700C. From thermodynamic calculations, thermal analysis, X-ray diffraction, and Raman spectroscopy, it is concluded that the intermediate oxycarbonate is a highly disordered, metastable, and weakly crystalline phase with a stoichiometry close to Ba[sub 2]Ti[sub 2]O[sub 5]Co[sub 3].

Metal Organic Resin Derived Barium Titanate: I, Formation of Barium Titanium Oxycarbonate Intermediate

Advanced dielectrics: Bulk ceramics and thin films

Thermal decomposition of (BaTi) citrates into barium titanate

Thin films of BaTiO3 and SrTiO3 were prepared by a chemical solution deposition method. The impact of the precursor on the processing, on the microstructure, and on the dielectric properties has been studied by systematically varying the alkyl chain length of the used Ba- and Sr-carboxylates. In addition, the effect of stabilizing the Ti-alkoxide precursor by acetylacetone has been investigated. The decomposition process, the crystallization behavior, and the film morphology were analyzed by glancing incidence XRD, reflectance FT-IR and field emission SEM. Distinct precursor effects on the thin film morphology and properties were revealed. Part of this influence can be attributed to an intermediate complex carbonate phase which forms for selected carboxylates with short alkyl chains. The high transformation temperature of this intermediate phase to the perovskite obviously has a marked influence on the crystallization and densification process of the alkaline earth titanate thin films. We correlate the morphological differences of the films to their dielectric properties.

Influence of Precursor Chemistry on the Formation of MTiO3 (M = Ba, Sr) Ceramic Thin Films

Clear, transparent gels of BaTi acetate have been prepared from titanium tetrabutylate (TBT), Ba acetate aqueous solution, isopropanol and acetic acid. Infrared spectroscopy and transmission electron microscopy (TEM) of such gels revealed linked clusters of polymer Ti oxyacetate with surface adsorbed Ba acetate. Spray dried Ti oxyacetate has been found to have the stoichiometric composition Ti 2 O 3 [CH 3 COO] 2 . Calcination of BaTi acetate gels to BaTiO 3 in air turned out to be a less favourable preparative route, because stable intermediate carbonate phases were formed. Corresponding to the high surface area and fine dispersion of Ba and Ti, BaTi acetate gels are higly reactive precursors for hydrothermal synthesis of BaTiO 3 . Nearly quantitative (> 99·7%) chemical reactions were obtained without using Ba excess at processing. TEM provided interesting information about the chemical mechanisms of hydrothermal processing.

Rao M S

Papers

しゅう酸チタニルの熱分解 i しゅう酸バリウムチタニル