Structural and thermal properties of Co-Cu-Fe hydrotalcite-like
compounds
JOURNAL OF SOLID STATE CHEMISTRY, 178 (1):
142-152 (2005)DOI: 10.1016/j.jssc.2004.10.039
Abstract
The structural properties and thermal decomposition processes of
Co-Cu-Fe ternary hydrotalcites (HT) have been studied through X-ray
diffraction, thermogravimetric measurements, Fourier-transform infrared
and Mossbauer spectroscopies. Due to the strong Jahn-Teller effect, the
Cu-Fe layered system is stabilized only in the presence of Co2+. At low
Co2+ contents, additional phases are segregated in the solids. X-ray
patterns show the presence of Cu(OH)(2) and CuO. The decomposition
process was investigated by in situ X-ray, in situ Mossbauer and FTIR
experiments. By increasing the temperature from 25 degreesC up to
180degreesC we observed that the structural disorder increases. This
effect has been likely attributed to the Co2+ --> CO3+ oxidation since
thermal decomposition was carried out under static air atmosphere. Part
of the Co3+ cations could migrate to the interlayer region, thus forming
a metastable compound that still has a layered structure. Collapse of
the layered structure was observed at about 200 degreesC. By further
increasing the temperature the system becomes more crystalline and the
formation Of CO3O4 is observed in the X-ray patterns. In Cu-rich HT,
some of the carbonate anions are released at temperatures higher than
550degreesC and this phenomenon is attributed to the formation of a
carbonate-rich phase. The specific surface area data present its highest
values in the temperature range where the collapse of the layered
structure takes place. (C) 2004 Elsevier Inc. All rights reserved.