Metal citrate polymerized complex thermal decomposition leading to the synthesis of BaTiO3: effects of the precursor structure on the BaTiO3 formation mechanism

Abstract

The study of BaTiO 3 crystallization from X-ray amorphous (Ba,Ti) polymeric organic powders has been carried out by comparing samples previously heat-treated in air at 250 and 400 uC. From thermal analysis, X-ray diffraction, infrared and Raman spectroscopies, and 13 C NMR spectroscopy, it has been found that the BaTiO 3 formation strongly depends upon the initial structure of the used precursor. It is concluded that an intermediate oxycarbonate phase was formed prior to the formation of BaTiO 3 above 550 uC when the precursor used was a (Ba,Ti)-mixed metal organic complex heat-treated at 250 uC, and a nanocrystalline BaCO 3 intermediate when the metal organic complex had been initially heat-treated at 400 uC. Although not well crystallized, thermoanalytical measurements, the unique XRD pattern, and new IR and Raman structural features revealed that such a metastable intermediate oxycarbonate phase has a stoichiometry close to Ba 2 Ti 2 O 5 ?CO 3 , which is characterized by having CO 3 22 groups different to those of pure BaCO 3 located, probably, in an open interlayer BaTiO 3 metastable structure. Irrespective of the used precursor, thermal decomposition of the (Ba,Ti)-mixed metal organic above 550 uC led to the formation of a mixture of tetragonal and hexagonal BaTiO 3 polymorphs rather than cubic. The synthesized BaTiO 3 powders are characterized by a high surface area of 40 m 2 g 21 up to 700 uC, and an equivalent particle size smaller than 25 nm. Raman spectra indicated asymmetry inside the TiO 6 octahedra of the BaTiO 3 structure.

Room-temperature photoluminescence ofBaTiO3: Joint experimental and theoretical study

“…At 350°C, the powder presents some diffraction peaks belonging to the well-known oxycarbonates that commonly appear during the synthesis of BT in those conditions. 30 Moreover, the shape of the pattern clearly indicates that a part of the powder is not yet crystallized. The BT crystalline phase can be observed from 400°C and is marked by ‫.ء‬ No intermediate titanate phase was observed, suggesting that a direct crystallization occurred from the structurally disordered phase.…”

Low-temperature synthesis of superfine barium strontium titanate powder by the citrate method

“…Similar phenomenon has been found in the synthesis of BaTiO 3 by the citrate method. It has been reported that the onset formation temperature of BaTiO 3 from the decomposition of an intermediate phase Ba 2 Ti 2 O 5 ÁCO 3 was about 550 8C, while the decomposition of the intermediate phase into BaCO 3 happened at 600-650 8C [16]. We believe that the reaction sequence can be applied to the present work on account of an analogous material nature and an essentially identical synthetic principle.…”

Synthesis and characterization of ultra fine barium calcium titanate, barium strontium titanate and Ba1−2xCaxSrxTiO3 (x=0.05, 0.10)

“…1 [14,15] indicating that this is the first crystalline phase in the powders and that it forms directly from the amorphous mixture. At 750 • C, the powders were much more crystalline and consisted mainly of pseudocubic perovskite phase accompanied by small amounts of barium carbonate and barium nitrate.…”

“…The FTIR spectra of these samples, which were dried and cal- became weaker as the calcination temperature was increased. A broad band at about 540 cm −1 is of typical Ti-O vibrations [14], which started to develop in the dry powders at 120 • C, while the band became sharper and narrower after calcination. After calcination at higher temperature, the band got separated into two bands at 1420 and 570 cm −1 [21][22][23][24][25] and this may be due to the formation of metal oxide bonds as suggested in the XRD results.…”