JST Vol. 21 (1) Jan. 2013 - Pertanika Journal - Universiti Putra ...

Physico-Chemical and Electrical Properties of Bismuth Chromate Solid Solutions
Arbritary weight ( percentage )
(d)
(c)
(b)
(a)
Fig.7: DTA thermogram of Bi 6Cr 2O 15
100 200 300 400 500 600 700 800
Temperature ( o C )
However, no shift was observed in the wavenumbers of Cr-O-Cr bond vibration, as well as Cr-O
stretching with the variation of the Cr content. The band of ~ 587 cm -1 and ~ 467 cm -1 in the
IR spectra was attributed to the vibration of Bi-O and Bi-O-Bi vibrations of [BiO 6] octahedral
units, respectively (Cheng et al., 2006; Rico-Fuentes et al., 2005).
The atomic weight of Bi is about four times larger than that of Cr. Moreover, the ionic radius
of Bi 3+ (1.20 Å) is larger than that of Cr 3+ (0.69 Å). Thus, Bi-O bond length is expected to be
longer and weaker compared to Cr-O bond. This may lead to the lowering of wavenumber (υ)
at 587 cm -1 and 467 cm -1 . The Bi contents for the compounds Bi xCr 2O δ, 4 ≤ x ≤ 7 are different
and it is expected that υ would decrease with increasing Bi content. However, from the IR
spectra obtained, the υ does not decrease with the increasing Bi content. It may due to Bi-O
Pertanika J. Sci. & Technol. 21 (1): 283 - 298 (2013)
1.02 %
0.89 %
0.96 %
0.77 %
Fig.8: The TGA thermographs of (a) Bi 4Cr 2O 12, (b) Bi 5Cr 2O 13.5, (c) Bi 6Cr 2O 15, and (d) Bi 7Cr 2O 16.5 with
their respective percentage weight loss
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