THERMAL-DECOMPOSITION OF PRECURSORS FOR BABIO3 PREPARED WITH AMINO-ACID COMPLEXES

BaBiO3 was prepared by several chemical and physical methods. The decomposition behaviour of the precursors was investigated using thermogravimetry, differential scanning calorimetry, evolved gas analysis, infrared spectroscopy and X-ray diffraction techniques. The self-propagating chemical decomposition (SCD) of the complexes with amino acids is compared with the decomposition of physical mixtures of barium and bismuth nitrates. with and without the addition of amino acids. Carbonate was detected as an intermediate from the IR spectra and was subsequently identified as BaCO3 by XRD. No complex carboxylate, such as Ba2Bi2O5CO3, was detected. Carbonates formed by SCD required very high temperatures, in excess of 950-degrees-C, before they decomposed. Hence, the BaBiO3 obtained by this method was contaminated with BaCO3. The intermediate carbonates which formed in mixtures with amino acids decompose at slightly lower temperatures, <850-degrees-C. Mixtures of the pure metal nitrates gave single-phase BaBiO3 at a considerably lower temperature, almost-equal-to 620-degrees-C.